Maternal thyroid dysfunction during gestation, preterm delivery, and birthweight. The Infancia y Medio Ambiente Cohort, Spain

Association between maternal and cord blood thyroid hormones, and urine iodine concentration with fetal growth

OBJECTIVES

We planned to evaluate the association of fetal and maternal thyroid hormones and maternal iodine status with neonates' anthropometric parameters.

METHODS

In this cross-sectional study, levels of thyrotropin were measured in maternal serum in the first trimester of pregnancy, and thyrotropin (TSH) and free thyroxin (fT4) were measured in cord blood serum samples at birth. Urinary iodine concentration (UIC) levels in random urine samples of mothers were measured in the third trimester of pregnancy. The relationship between UIC and thyroid hormone levels of mothers with neonates' anthropometric birth parameters of neonates was evaluated.

RESULTS

One hundred eighty-eight mother-newborn pairs completed the study. Mean (SD) of cord blood TSH (CB-TSH), cord blood-free thyroxin (CB-FT4) values, and maternal TSH (M-TSH) levels were 8.8 (7.3) mIU/L, 1.01 (0.2) ng/dL, and 2.2 (0.9) mIU/L, respectively. After adjusting for confounders, there was a positive significant association between female neonate length and maternal TSH and log log-transformed CB TSH (LN_CB-TSH) (p<0.05). Median UIC (Q1-Q3) was 157 (53-241) μg/L, and there was no association between birth weight, birth length, and head circumferences of neonates and mothers' UIC (p>0.05).

CONCLUSIONS

We found a positive correlation between maternal TSH in the first trimester of pregnancy and the birth length of newborns, and a negative correlation was observed between CB-TSH and birth length in girls, but it did not provide conclusive evidence for the relationship between maternal and neonatal thyroid hormone levels and birth weight. There was no association between maternal UIC levels in the third trimester and birth anthropometric parameters.

Bone development in fetuses with intrauterine growth restriction caused by maternal endocrine-metabolic dysfunctions

Intrauterine growth restriction (IUGR) affects a large proportion of infants, particularly in underdeveloped countries. Among the main causes of IUGR, maternal endocrine-metabolic dysfunction is highlighted, either due to its high incidence or due to the severity of the immediate and mediated changes that these dysfunctions cause in the fetus and the mother. Although the effects of endocrine and metabolic disorders have been widely researched, there are still no reviews that bring together and summarize the effects of these conditions on bone development in cases of IUGR. Therefore, the present literature review was conducted with the aim of discussing bone changes observed in fetuses with IUGR caused by maternal endocrine-metabolic dysfunction. The main endocrine dysfunctions that occur with IUGR include maternal hyperthyroidism, hypothyroidism, and hypoparathyroidism. Diabetes mellitus, hypertensive disorders, and obesity are the most important maternal metabolic dysfunctions that compromise fetal growth. The bone changes reported in the fetus are, for the most part, due to damage to cell proliferation and differentiation, as well as failures in the synthesis and mineralization of the extracellular matrix, which results in shortening and fragility of the bones. Some maternal dysfunctions, such as hyperthyroidism, have been widely studied, whereas conditions such as hypoparathyroidism and gestational hypertensive disorders require further study regarding the mechanisms underlying the development of bone changes. Similarly, there is a gap in the literature regarding changes related to intramembranous ossification, as most published articles only describe changes in endochondral bone formation associated with IUGR. Furthermore, there is a need for more research aimed at elucidating the late postnatal changes that occur in the skeletons of individuals affected by IUGR and their possible relationships with adult diseases, such as osteoarthritis and osteoporosis.

Overt hypothyroidism in pregnancy and language development in offspring: is there an association?

PURPOSE

Overt hypothyroidism during pregnancy is linked to various obstetric complications, such as premature birth and fetal death. While some studies have shown that maternal hypothyroidism can impact a child's Intelligence Quotient (IQ) and language development, findings are controversial. The aim of this study was to explore the connection between treated maternal hypothyroidism during pregnancy and offspring neurodevelopment, focusing on learning and language and examining related maternal obstetric complications.

METHODS

Group 1 included 31 hypothyroid women with elevated thyroid stimulating hormone (TSH) (> 10 mU/L, > 10 µIU/mL) during pregnancy, and Group 2 had 21 euthyroid women with normal TSH levels (0.5-2.5 mU/L, 0.5-2.5 µIU/mL). Children underwent neuropsycological assessments using the Griffiths-II scale.

RESULTS

Pregnancy outcome showed an average gestational age at delivery of 38.2 weeks for hypothyroid women, compared to 40 weeks for controls, and average birth weight of 2855.6 g versus 3285 g for controls, with hypothyroid women having children with higher intrauterine growth restriction (IUGR) prevalence and more caesarean sections. The 1-min APGAR score was lower for the hypothyroid group's children, at 8.85 versus 9.52. Neuropsychological outcomes showed children of hypothyroid mothers scored lower in neurocognitive development, particularly in the learning and language subscale (subscale C), with a notable correlation between higher maternal TSH levels and lower subscale scores.

CONCLUSION

Fetuses born to hypothyroid mothers appeared to be at higher risk of IUGR and reduced APGAR score at birth. Neurocognitive development seemed to affect language performance more than the developmental quotient. This alteration appeared to correlate with the severity of hypothyroidism and its duration.

Association of maternal thyroid disease with obesity in child

OBJECTIVES

During pregnancy, many women develop thyroid disorders, which can result in fetal and neonatal development defects. We investigated whether maternal thyroid dysfunction would affect their children's growth and obesity.

STUDY DESIGN

We conducted a nationwide population-based cohort study using a combination of data from several Korean nationwide registries to investigate the association between maternal thyroid dysfunction, offspring growth, and obesity. Childhood growth was repeatedly measured at three periods of age from 42 to 80 months, using body mass index (BMI).

RESULTS

A total of 1,123,499 women were enrolled in this study; 78,902 (7.0 %) had pre-pregnancy thyroid disease. Significant association was found between maternal hyperthyroidism and obesity in all children aged 42-66 months (42-54 months, adjusted odds ratio (aOR) 0.93, 95 % confidence interval (CI) 0.89-0.98; 54-66 months, aOR 0.93, 95 % CI 0.87-0.99), but not at later ages. In the analysis by sex, maternal hyperthyroidism was associated with childhood obesity in boys, whereas it was not associated with those in girls of any age. No association was observed between maternal hypothyroidism and child BMI or obesity.

CONCLUSIONS

The association between maternal thyroid function and obesity in offspring is attenuated from early to late childhood, suggesting that many other factors may be involved in developing childhood obesity.

Effect of Iodine Nutrition Status on Thyroid Function and Pregnancy Outcomes

Iodine is essential for normal thyroid function, supporting healthy fetal and child development. The relevance between maternal iodine nutrition status and pregnancy outcomes remains controversial. The aim was to explore whether urinary iodine concentrations (UIC)/urinary creatinine (UCr) was associated with thyroid function and adverse pregnancy outcomes. This study was performed in the Department of Endocrinology and Metabolism of the First Affiliated Hospital of Nanjing Medical University. A total of 212 pregnant women were enrolled from May 2018 to November 2021, from the first visit until postpartum. Maternal serum samples were obtained in the second half of pregnancy, and then thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), UIC, and UCr were tested. The correlation of UIC/UCr, which represented maternal iodine nutrition status, with TSH, FT4, and FT3 was studied using linear regression. And we assessed associations between UIC/UCr and pregnancy outcomes. Notably, we explored consistency between UIC/UCr and the incidence of low birth weight (LBW) by application of logistic regression analysis. A total of 212 women were divided into 3 groups according to the upper and lower quartiles of UIC/UCr. There were 53 women in group 1 (UIC/UCr < 106.96 ug/g), 106 women in group 2 (UIC/UCr 106.96-259.08 ug/g), and 53 women in group 3 (UIC/UCr > 259.08 ug/g). The level of UIC/UCr had a negative correlation with FT4 (r =  - 0.139, p = 0.043) but a positive correlation with TSH (r = 0.096, p = 0.162 > 0.05). There was a significant difference in the incidence of LBW among the 3 groups (p = 0.007). Logistic regression analysis found that the level of UIC/UCr was an independent factor for LBW (p = 0.048, OR = 0.991, 95%CI (0.982, 0.999)). The receiver operating characteristic (ROC) curve showed that the area under the curve (AUC) for UIC/UCr predicting the incidence of low birth weight was 0.687 (p = 0.013, 95%CI 0.575, 0.799). Lower UIC/UCr during pregnancy was associated with higher FT4 and lower TSH. And iodine deficiency during pregnancy is a risk factor for low birth weight. Our findings indicated that more attention should be paid to the appropriate iodine nutrition status in pregnant women, which can help prevent suffering from adverse pregnancy outcomes.

Relationship between the Central and Peripheral Thyroid Sensitivity Indices and Fetal Macrosomia: A Cohort Study of Euthyroid Pregnant Women in China

(1) Background: To explore the correlation between central and peripheral thyroid sensitivity indices and macrosomia in euthyroid pregnant women and to provide clinical basis for the prevention and treatment of macrosomia. (2) Methods: This study is a prospective study. A total of 1176 euthyroid women in early pregnancy in the obstetrics department of Peking University International Hospital from December 2017 to March 2019 were enrolled. The women were divided into two groups, namely the macrosomia and non-macrosomia groups, according to birth weight. (3) Results: The level of free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), thyroid feedback quantile-based index (TFQI), thyrotropin-T4 resistance index (TT4RI), thyroid-stimulating hormone index (TSHI), and free triiodothyronine/free thyroxine (FT3/FT4) in the macrosomia group was higher than that in the non-macrosomia group (p < 0.05). The multivariate logistic regression model showed that FT3, TFQI, TT4RI, TSHI, and FT3/FT4 were independent risk factors for macrosomia in early pregnancy after adjusting for age, body mass index, parity, blood pressure, blood glucose, and blood lipid levels (p < 0.05, respectively). (4) Conclusions: TFQI, TT4RI, TSHI, and FT3/FT4 are independent risk factors for fetal macrosomia in early pregnancy in euthyroid women.

Prediction of preterm delivery based on thyroid peroxidase antibody levels and other identified risk factors

OBJECTIVE

Thyroid dysfunction and TPOAb positivity during pregnancy are associated with adverse pregnancy outcomes such as preterm delivery. The aim of this study was to predict preterm delivery based on identified risk factors, especially TPOAb levels.

STUDY DESIGN

A secondary analysis was run on data collected in the Tehran Thyroid and Pregnancy study (TTPs). We used the data of 1515 pregnant women with singletons. The association between risk factors and preterm birth (delivery before 37 completed weeks of gestation) was investigated in univariate analysis. Multivariate logistic regression analysis was performed to identify independent risk factors, and a stepwise backward elimination method was used to determine the helpful combination of risk factors. The nomogram was developed based on a multivariate logistic regression model. The performance of the nomogram was evaluated using a concordance index and calibration plots with bootstrap samples. Statistical analysis was performed using STATA software package; the significance level was set at P < 0.05.

RESULTS

Based on multivariate logistic regression analysis, a combination of previous preterm delivery [OR: 5.25; 95 %CI: (2.13-12.90), p < 0.01], TPOAb [OR: 1.01; 95 %CI: (1.01-1.02), and T4 [OR: 0.90; 95 %CI: (0.83-0.97); p = 0.04] as independent risk factors that most precisely predicted preterm birth. The area under the curve (AUC) was 0.66 (95% CI: 0.61-0.72). The calibration plot suggests that the fit of the nomogram is reasonable.

CONCLUSION

A combination of T4, TPOAb, and previous preterm delivery was identified as independent risk factors that accurately predicted preterm delivery. The total score obtained based on the nomogram designed based on risk factors can predict the risk of preterm delivery.

The impact of covid-19 on thyroid function tests in pregnancy

PURPOSE

To investigate the effects of laboratory-confirmed SARS-CoV-2 infection on thyroid function tests (TFTs) in pregnant women and to evaluate whether TFT changes are related to the severity and prognosis.

METHODS

Consecutive pregnant women tested for SARS-CoV-2 by RT-PCR at Ankara City Hospital were recruited between January 2021 and September 2021. Thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3), thyroid peroxidase antibody (anti-TPO), and thyroglobulin antibody (anti-TG) were measured on admission.

RESULTS

Among 747 eligible pregnant women with the same baseline characteristics, 369 RT-PCR-positive women in the patient group and 378 RT-PCR-negative women in the control group were included in the analyses. Pregnant women in the patient group had significantly lower TSH, FT4, FT3, Anti TPO, and Anti TG concentrations compared with those in the control group (p < 0.001). The proportion of patient groups with mild, moderate, severe, and critical diseases were 297 (80.4%), 40 (10.8%), 17 (4.6%), and 15 (4.2%), respectively, among which with the moderate, severe, and critical disease had significantly lower FT3 values (2.5 vs 2.19 pg/mL, p < 0.001) and higher nonthyroidal illness syndrome (NTIS) (29.2 vs. 8.4%, p < 0.001) than those with mild disease. Lower FT3 values increased the risk of ICU admission, NICU admission, and severe disease (p < 0.001). FT3 and TSH correlated positively with lymphocytes (p < 0.001) and negatively correlated with C-reactive protein (CRP) (p < 0.001, p = 0.005).

CONCLUSION

The SARS-CoV-2 infection seems to have an impact on the TFTs of pregnant women, and particularly FT3 level seems to be correlated with disease severity.

Maternal Iodine Status and Birth Outcomes: A Systematic Literature Review and Meta-Analysis

Background & aims: Iodine is important for thyroid function during pregnancy to support fetal growth, but studies of maternal iodine status and birth outcomes are conflicting. We aimed to quantify the association between iodine status and birth outcomes, including potential threshold effects using nonlinear dose−response curves. Methods: We systematically searched Medline and Embase to 10 October 2022 for relevant cohort studies. We conducted random-effects meta-analyses of urinary iodine concentration (UIC), iodine:creatinine ratio (I:Cr), and iodide intake for associations with birth weight, birth weight centile, small for gestational age (SGA), preterm delivery, and other birth outcomes. Study quality was assessed using the Newcastle-Ottawa scale. Results: Meta-analyses were conducted on 23 cohorts with 42269 participants. Birth weight was similar between UIC ≥ 150 μg/L and <150 μg/L (difference = 30 g, 95% CI −22 to 83, p = 0.3, n = 13, I2 = 89%) with no evidence of linear trend (4 g per 50 μg/L, −3 to 10, p = 0.2, n = 12, I2 = 80%). I:Cr was similar, but with nonlinear trend suggesting I:Cr up to 200 μg/g associated with increasing birthweight (p = 0.02, n = 5). Birthweight was 2.0 centiles (0.3 to 3.7, p = 0.02, n = 4, I2 = 0%) higher with UIC ≥ 150 μg/g, but not for I:Cr. UIC ≥ 150 μg/L was associated with lower risk of SGA (RR = 0.85, 0.75 to 0.96, p = 0.01, n = 13, I2 = 0%), but not with I:Cr. Conclusions: The main risk of bias was adjustment for confounding, with variation in urine sample collection and exposure definition. There were modest-sized associations between some measures of iodine status, birth weight, birth weight centile, and SGA. In pregnancy, we recommend that future studies report standardised measures of birth weight that take account of gestational age, such as birth weight centile and SGA. Whilst associations were modest-sized, we recommend maintaining iodine sufficiency in the population, especially for women of childbearing age on restricted diets low in iodide.

Thyroid hormones and carnitine in the second trimester negatively affect neonate birth weight: A prospective cohort study

BACKGROUND

Maternal thyroid hormones and carnitine are reported to affect neonate birth weight during the second trimester, which is one of the most important markers for fetal growth and perinatal mortality and morbidity. Nevertheless, the effect of thyroid hormone and carnitine in the second trimester on birth weight has yet to be understood.

METHOD

This was a prospective cohort study with 844 subjects enrolled during the first trimester. Thyroid hormones, free carnitine (C0), neonate birth weight, as well as other related clinical and metabolic data were collected and assessed.

RESULTS

Pre-pregnancy weight and body mass index (BMI) as well as neonate birth weight were significantly different among different free thyroxine (FT4) level groups. Maternal weight gain and neonate birth weight varied significantly when grouped by different thyroid-stimulating hormone (TSH) levels. There was a significantly positive correlation between C0 and TSH (r = 0.31), free triiodothyronine (FT3) (r = 0.37), and FT4 (r = 0.59) (all P < 0.001). In addition, a significantly negative influence was found between birth weight and TSH (r = -0.48, P = 0.028), so as C0 (r = -0.55, P < 0.001) and FT4 (r = -0.64, P < 0.001). Further assessment detected a stronger combined effect of C0 and FT4 (P < 0.001) and of C0 and FT3 (P = 0.022) on birth weight.

CONCLUSION

Maternal C0 and thyroid hormones are of great importance in neonate birth weight, and routine examination of C0 and thyroid hormones during the second trimester has a positive effect on the intervention of birth weight.

Serum lipid profile in relation to free thyroxine and the effect of levothyroxine treatment on lipids in patients with isolated hypothyroxinemia during pregnancy: a single-center retrospective study

BACKGROUND

Thyroid function is widely considered a lipid metabolism regulator. However, studies on lipid metabolism in pregnant women with low free thyroxine (FT₄) levels are limited and inconclusive. Furthermore, the association between maternal FT₄ deficiency and adverse lipid metabolic parameters is unknown. Therefore, we aimed to investigate this association and the effects of levothyroxine (L-T₄) treatment on these metabolic indicators.

METHODS

This retrospective study included 164 patients with isolated hypothyroidism (IH) (FT₄ levels below the 5^th percentile with normal thyroid stimulating hormone levels according to the gestational-specific reference range) and 407 euthyroidism patients (control group who had regular antenatal examinations at Zhejiang Provincial People's Hospital, Hangzhou, China) between January 1, 2019, and December 31, 2020. Patients with IH were divided into levothyroxine (L-treatment group, n = 77) and dietary iodine supplement treatment groups (dietary treatment group, n=87) according to the hospital's treatment policy and clinical experience. The intervention lasted for at least 8 weeks. Metabolic indicators, including thyroid function and lipid parameters, were collected at least twice before and after the intervention. Other data collected included maternal age, history of abortion, prepregnancy BMI, and gestational weight gain (Fig. 1).

RESULTS

Compared with the control group, Patients with IH had a higher degree of dyslipidemia, reflected in elevated total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein B (Apo B) levels. In IH patients, an inverse correlation was found between FT₄ and TG levels, which remained after adjusting for prepregnancy BMI. The L-treatment group demonstrated a significantly slower rate of hypercholesterolemia progression during pregnancy than the dietary treatment group. In addition, there was a relationship between the therapeutic effect and the degree of disease, with the main factors being FT₄, TSH and TG levels prior to starting treatment.

CONCLUSIONS

Low FT₄ levels were associated with elevated blood lipid levels. Serum FT₄ and lipid levels in patients could be improved by medical intervention.

Obstetric and offspring outcomes in isolated maternal hypothyroxinaemia: a systematic review and meta-analysis

OBJECTIVE

To examine the association between isolated maternal hypothyroxinaemia (IMH) and adverse obstetric outcomes and offspring outcomes and also investigate the effects of levothyroxine therapy on IMH for the above outcomes.

METHODS

We systematically searched PubMed, EMBASE, and Cochrane Library, and the reference lists of key reviews were hand searched on June 9, 2021. Two authors independently screened titles/abstracts. Full articles were further assessed if the information suggested that the study met the inclusion/exclusion criteria, and two researchers performed data extraction and risk-of-bias assessment using standardized tables. Summary relative risks or the mean difference between maternal effects and offspring outcomes were calculated by a random-effects model.

RESULTS

We identified 38 eligible articles (35 cohort studies and two randomized controlled trials [RCT]). Meta-analysis showed that maternal IMH was associated with increased gestational diabetes mellitus, preterm premature rupture of membranes, preterm birth, fetal distress, and macrosomia outcomes in IMH compared to euthyroid women, and the relative risks were 1.42 (1.03-1.96), 1.50 (1.05-2.14), 1.33 (1.15-1.55), 1.75 (1.16-2.65) and 1.62 (1.35-1.94), respectively. IMH was not associated with placenta previa, gestational hypertension, pre-eclampsia, intrauterine growth restriction, and offspring outcomes like birth weight, low birth weight infants, fetal macrosomia, neonatal intensive care, neonatal death, or fetal head circumference. In addition, we did not find an association between IMH and adverse offspring cognitive defects. Due to insufficient data for meta-analysis, it failed to pool the evidence of levothyroxine's therapeutic effect on IMH and their offspring.

CONCLUSIONS AND RELEVANCE

IMH in pregnancy may relate to a few maternal and offspring outcomes. Moreover, there is currently no sufficient evidence that levothyroxine treatment during pregnancy reduces adverse maternal outcomes and disability in offspring. Further investigation to explore the beneficial effects of levothyroxine therapy is warranted.

Association between isolated maternal hypothyroxinemia during the first trimester and adverse pregnancy outcomes in Southern Chinese women: a retrospective study of 7051 cases

Background

The association between isolated maternal hypothyroxinemia (IMH) and adverse pregnancy outcomes is still controversial. This study aimed to evaluate the association between IMH during the first trimester and adverse pregnancy outcomes in southern Chinese women.

Methods

This was a hospital-based, retrospective cohort study. The records of 7051 women, including 1337 IMH women and 5714 euthyroid women who had a singleton pregnancy and accepted routine prenatal service at the Third Affiliated Hospital of Sun Yat-Sen University from January 2015 to September 2018, were extracted from the electronic medical records system in this study. Thyroid functions [thyroid-stimulating hormone (TSH), free thyroxine (fT4) and anti-thyroperoxidase autoantibody (TPO-Ab)] had to be measured before 13 weeks and 6 days of gestation. The chi-square test and multivariate logistic regression analysis were applied to evaluate the association between IMH during the first trimester and adverse pregnancy outcomes.

Results

Prepregnancy obesity [prepregnancy body mass index (preBMI) ≥ 25 kg/m2] was found to be more common in the IMH group (11.2% vs. 6.1%) (P < 0.05). The prevalence of gestational diabetes mellitus (GDM), postpartum haemorrhage (PPH), macrosomia and large for gestational age (LGA) was higher in the IMH group. However, after using multivariate logistic regression analysis to adjust for confounders (maternal age, educational levels and preBMI), only LGA was shown to be associated with an increased risk in IMH women [adjusted OR: 1.27 (95% CI 1.044–1.566)]. The prevalence of preterm delivery (either < 37 or < 34 weeks), gestational hypertension, preeclampsia, placenta previa, placental abruption, premature rupture of membrane (PROM), intrauterine growth restriction (IUGR), polyhydramnios, stillbirth, small for gestational age (SGA) and low Apgar score did not increase.

Conclusion

IMH during the first trimester did not increase any risk of adverse pregnancy outcomes in southern Chinese women except LGA.

Association between phenols and thyroid hormones: The role of iodothyronine deiodinase genes

Previous literature on prenatal phenol exposure and thyroid hormone (TH) alteration is conflicting, and the possible mechanisms of action involved remain unclear. We aimed to examine the association between prenatal phenol exposure and levels of maternal and neonatal THs, as well as the possible role of iodothyronine deiodinase (DIO) gene polymorphisms in this relation. We studied 387 Spanish mother-neonate pairs with measurements of maternal phenols, total triiodothyronine (TT3) and free thyroxine (FT4), maternal and neonatal thyroid-stimulating hormone (TSH), and maternal genotypes for single nucleotide polymorphisms in the DIO1(rs2235544) and DIO2(rs12885300) genes. We implemented multivariate linear and weighted quantile sum (WQS) regressions to examine the association between phenols and THs (including sex-stratified models for neonatal TSH) and investigated effect modification of genotypes in the maternal phenol-TH associations. In single exposure models, we found negative associations between maternal triclosan (TCS) and neonatal TSH (% change [95%CI]: -2.95 [-5.70, -0.11], per twofold phenol increase) - stronger for girls - and less clearly for maternal ethylparaben (EPB) and TSH (-2.27 [-4.55, 0.07]). In phenol mixture models, we found no association with THs. In the genetic interaction models, we found some evidence of effect modification of DIO gene polymorphisms with stronger negative associations between methylparaben (MPB), propylparaben (PPB), butylparaben (BPB) and TT3 as well as bisphenol A (BPA) and FT4 for DIO1(rs2235544)-CC. Stronger inverse associations for genotypes DIO2(rs12885300)-CC and DIO2(rs12885300)-CT and positive ones for DIO2(rs12885300)-TT were also reported for BPA and FT4. In conclusion, we found some evidence of an association between phenols and TSH during pregnancy and at birth in single exposure models, the latter being stronger for girls. Since no association was observed between maternal levels of phenols and TT3 or FT4, the possible role of the genetic background in these associations warrants further investigation.

Early pregnancy PM2.5 exposure and its inorganic constituents affect fetal growth by interrupting maternal thyroid function

Early pregnancy is crucial for fetal growth. Maternal thyroid hormone is critical for fetal growth and can be disturbed under exogenous exposure. However, it's uncertain whether exposure to PM_2.5 and inorganic constituents during early pregnancy can affect TH and fetal growth. We focused on the associations of early-pregnancy PM_2.5 and inorganic constituents with fetal growth and maternal THs. PM_2.5 concentration was estimated using a satellite-based spatiotemporal model. Fetal biparietal diameter (BPD), head circumference (HC), femur length (FL), and humerus length (HL) were measured by ultrasonography at median 15.6, 22.2, and 33.1 gestational weeks. Levels of 28 PM_2.5 constituents were measured in a sub-group of 329 pregnancies. Maternal serum free thyroxine (fT4), free triiodothyronine, and thyroid-stimulating hormone levels were measured at 14 weeks of gestation. Mixed-effect models and multiple linear regression were applied to evaluate the associations of PM_2.5 and its constituents with fetal growth measures. Mediation analysis was used to examine the mediating role of the THs. Results showed that each 10 μg/m³ increase in PM_2.5 was associated with 0.20 mm reductions in BPD (95%CI: 0.33, -0.01), 0.27 mm decreases in FL (95%CI: 0.40, -0.13), and 0.36 decreases in HL (95%CI: 0.49, -0.23). Per 10 μg/m³ increment in PM_2.5 was correlated with 5.82% decreases in the fT4 level (95% CI: 8.61%, -2.96%). FT4 accounted for 14.3% of PM_2.5 exposure-induced change in BPD at first follow-up. Al (β = -2.91, 95%CI: 5.17, -0.66), Si (β = -1.20, 95%CI: 2.22, -0.19), K (β = -3.09, 95%CI: 5.41, -0.77), Mn (β = -47.20, 95%CI: 83.68, -10.79) and Zn (β = -3.02, 95%CI: 5.55, -0.49) were associated with decreased fetal BPD, especially in first follow-up. Zn (β = -38.12%, 95% CI: 58.52%, -8.61%) was also associated with decreased fT4 levels. Overall, early pregnancy exposure to PM_2.5 and its constituents was associated with fetal growth restriction and decreased maternal fT4 levels might mediate the effect of PM_2.5.

The Impact of First Trimester TSH Level on Fetal Growth and Post-Term Pregnancy

Objective:  First trimester thyroid-stimulating hormone (TSH) level is an important determiner of neonatal outcome. In this study we investigated the relationship between first-trimester TSH level and fetal birthweight. Materials-Methods: First-trimester serum TSH, age, gravidity, parity, body mass index (BMI), gestational age, and birth weight were analyzed. Patients were divided two ways. The first division- group 1 with TSH < 2.5 mU/l, group 2 with TSH > 2.5 mU/l). The second division- group 3 with TSH < 4 mU/l and group 4 with TSH > 4 mU/l). Results: The study included 302 patients. High TSH levels are associated with an increased risk of macrosomic and post-term babies. A significant association was found for both thresholds of 2.5 and 4.0 mU/l. However, this relation was not significant after binary logistic regression. Conclusion: High maternal first trimester TSH levels are not associated with birth weight after separating out macrosomia-related factors.

Postnatal Serum Total Thyroxine Level Associated with Short- and Long-Term Anthropometric Outcomes in Very Preterm Infants

Thyroxine (T4) importantly regulates the growth of newborns. Compared to fetuses with equivalent gestational ages, very preterm infants (VPIs) often experience relatively low thyroxinemia, with a normal thyroid-stimulating hormone (TSH) concentration < 10 μIU/mL. However, there is continued debate regarding postnatal thyroxine supplementation for VPIs with normal TSH and transitionally low thyroxinemia. Little research has explored the role of the postnatal total T4 (TT4) serum concentration on the growth of VPIs. In this study, we aim to clarify whether the postnatal thyroxine concentration is associated with the short- and long-term growth outcomes of VPIs. A total of 334 surviving VPIs in our previously reported cohort, born in the period August 2007−July 2016, were enrolled. The exposure variable was the postnatal TT4 concentration at 1 month old. The primary outcomes were body weight increments over 28 days after the screening and anthropometric outcomes at the corrected age of 24 months old. Infants with any hormonal replacement, severe brain injury, congenital anomaly, or cerebral palsy were excluded. In total, 290 (86.8%) VPIs were included for analysis. In the 28 days after thyroid function screening, the TT4 concentration was found to have a significant association with positive increments in body weight (mean increment: 25.7 g per 1 μg/dL; p < 0.001) and a positive body weight z-score (mean increment: 0.039 per 1 μg/dL; p = 0.037), determined by generalized estimating equation analysis. At the corrected age of 24 months old, a higher postnatal TT4 concentration was associated with a lower body mass index (mean coefficient: −0.136; 95% CI: −0.231 to −0.041, p = 0.005) and lower body mass index z-score (mean coefficient: −0.097; 95% CI: −0.170 to −0.024, p = 0.009). Infants with a TT4 concentration > 6.4 ug/dL had significantly lower odds of overweight status (odds ratio: 0.365; 95% CI: 0.177 to 0.754, p = 0.006). We conclude that the postnatal TT4 concentration is associated with a positive increment in body weight in the short term. At the same time, the postnatal TT4 concentration is associated with lower odds of overweight status after long-term follow-up.

OUP accepted manuscript

Context

Adequate iodine intake is essential throughout life. Key dietary sources are iodized salt and animal products, but dietary patterns in Europe are changing, for example toward lower salt intake and a more plant-based diet.

Objective

To review iodine intake (not status) in European populations (adults, children, and pregnant women) to identify at-risk groups and dietary sources.

Data sources

PubMed, Embase, and Cochrane databases, as well as European national nutrition surveys were searched for data on had iodine intake (from dietary assessment) and sources of iodine, collected after 2006.

Data selection

In total, 57 studies were included, comprising 22 national surveys and 35 sub-national studies. Iodine intake data were available from national surveys of children aged <10 years (n = 11), 11–17 years (n = 12), and adults (n = 15), but data from pregnancy were only available from sub-national studies.

Results

Iodine intake data are lacking—only 17 of 45 (38%) European countries had iodine-intake data from national surveys. Iodine intake reported from national surveys was below recommendations for: (1) children aged <10 years in 2 surveys (18%), (2) boys and girls aged 11–17 years in 6 (50%) and 8 (68%) surveys, respectively, and (3) adult men and women in 7 (47%) and 12 (80%) surveys, respectively. In pregnant women, intake was below recommendations except where women were taking iodine-containing supplements. Just 32% of national surveys (n = 7) included iodized salt when estimating iodine intake. Milk, dairy products, fish, and eggs were important contributors to intake in many countries, suggesting limited sources in plant-based diets.

Conclusion

Results are limited by the challenges of dietary assessment for measuring iodine intake. Future national surveys should include iodine intake. Policy makers should consider dietary sources alongside any iodized salt policies when considering methods for improving population iodine intake.

Systematic Review Registration

PROSPERO 2017 CRD42017075422.

Could maternal thyroid function during pregnancy affect daughters' age at menarche through child growth? A mediation analysis

Early menarche is associated with adverse health outcomes during adolescence as well as breast and other reproductive cancers later in adulthood. However, the causes of early menarche and the pathways through which they operate are not fully understood. Though maternal thyroid function during pregnancy affects child growth, and rapid childhood growth is associated with a decreased age at menarche, the relationship between prenatal maternal thyroid function and daughters' age at menarche has not been examined. We conducted a mediation analysis in a historical cohort of 260 mother-child pairs to estimate the total and indirect effects of maternal prenatal thyroid function on daughters' age at menarche. No association was observed between thyroid stimulating hormone (TSH) or anti-thyroid peroxidase antibodies (ATPO) and daughters' age at menarche. Using a sample-specific, a-priori cutoff at the 10th percentile, low levels of maternal free thyroxine (FT4) were associated with earlier daughter age at menarche, with a hazard ratio (95 % CI) of 1.70 (1.02, 2.84) comparing the bottom 10th percentile with the top 90th percentile of exposure levels. Higher maternal FT4 was associated with rapid child weight gain from ages 5-9, and rapid child weight gain from ages 5-9 was associated with earlier age at menarche; the estimated indirect effect of this pathway was null. While maternal FT4 is associated with earlier age at menarche in daughters, this is not mediated by rapid weight gain in our study population, suggesting that maternal FT4 is operating through a different pathway.

Thyroid hormones in relation to toxic metal exposure in pregnancy, and potential interactions with iodine and selenium

BACKGROUND

Several endocrine-disrupting metals may affect thyroid function, but the few available studies of exposure during pregnancy and thyroid hormones are inconclusive.

OBJECTIVE

To explore if environmental exposure to cadmium (Cd), lead (Pb), and methylmercury (MeHg) impacts thyroid function in pregnancy, and interacts with iodine and selenium status.

METHODS

Women in a Swedish birth cohort provided blood and urine samples in early third trimester. Concentrations of erythrocyte Cd, Pb, and Hg (n = 544), urinary Cd and iodine (n = 542) and plasma selenium (n = 548) were measured using inductively coupled plasma-mass spectrometry.Free and total thyroxine (fT4, tT4) and triiodothyronine (fT3, tT3), and thyroid stimulating hormone (TSH), were measured in plasma (n = 548) with electrochemiluminescence immunoassays. Metal-hormone associations were assessed in regression models, and metal mixture effects and metal-nutrient interactions were explored in Bayesian kernel machine regression (BKMR).

RESULTS

In multivariable-adjusted regression models, a doubling of urinary Cd was associated with a mean increase in tT4 of 2.7 nmol/L (95% CI: 0.78, 4.6), and in fT3 and tT3 of 0.06 pmol/L (0.02, 0.10) and 0.09 nmol/L (0.05, 0.13), respectively. A doubling of urinary Cd was associated with a -0.002 (-0.003, -0.001) and -0.03 (-0.05, -0.02) decrease in the fT4:tT4 and fT3:tT3 ratio, respectively. A doubling of erythrocyte Hg (>1 µg/kg) was associated with a decrease in fT3 and tT3 by -0.11 pmol/L (-0.16, -0.05) and -0.11 nmol/L (-0.16, -0.06), respectively, and a -0.013 (-0.02, -0.01) decrease in the fT3:fT4 ratio. BKMR did not indicate any mixture effect of toxic metals or interactions between metals and iodine or selenium in relation to the hormones.

CONCLUSION

Our findings suggest that exposure to Cd and Hg, at levels globally prevalent through the diet, may affect thyroid function during pregnancy, independently of iodine and selenium levels. Further studies on potential implications for maternal and child health are warranted.

Maternal iodine deficiency: a newborns' overweight risk factor? A prospective study

OBJECTIVES

Childhood obesity and iodine deficiency are global public health concerns. Whether maternal iodine status mediates overweight in infancy has yet to be explored. We aimed to assess the relationship between maternal iodine status and infant birth weight, including small and large for gestational age (SGA and LGA, respectively).

METHODS

A prospective study was carried out among 134 mother-infant pairs from Israel. Maternal iodine intake and status were estimated via questionnaire and serum thyroglobulin (Tg), respectively. Estimated iodine intake below the Recommended Daily Allowance for iodine sufficiency in pregnancy (220 μg/d) considered Inadequate. Maternal and neonatal thyroid function and anthropometric measurements, as well as maternal thyroid antibodies were also tested.

RESULTS

After screening, 118 participants met the inclusion criteria (distributed trimesters I, II and III: n = 3, n = 21, and n = 94, respectively). There was a negative association of iodine intake with Tg values among the study population. Maternal median Tg value was higher than the sufficiency cutoff (16.5 vs 13 µg/L), indicating insufficient iodine status. No SGA cases were found. Inadequate iodine intake was associated with maternal isolated hypothyroxinemia (OR = 3.4; 95% CI 1.2, 9.9) and higher birthweight (including macrosomia and LGA) rates. A suggestive association of elevated Tg with a greater risk of LGA was observed. Offsprings' birth weight percentiles were associated with Tg values in pregnant women with suggestive sufficient iodine status (n = 62, R² = 0.11, p < 0.05).

CONCLUSIONS

Iodine status during pregnancy can be associated with newborn anthropometric index. Maternal inadequate iodine intake may alter fetal growth and might increase the risk of LGA among newborns. These initial findings support the need to further study the impact of iodine deficiency on newborns overweight in Israel and elsewhere.

Effects of isolated maternal hypothyroxinemia on adverse pregnancy outcomes

PURPOSE

There are conflicting results about the effects of maternal hypothyroidism (IMH) on adverse pregnancy outcomes. This study aimed to investigate the relationship between IMH identified in the first trimester of gestation and adverse pregnancy outcomes.

METHODS

In this prospective cohort study, we used data from the Tehran Thyroid and Pregnancy study (TTPs). To diagnose IMH, we considered a threshold of 2.04 for FTI, which was based on the 10th percentile of this marker identified in the 1st trimesters. A generalized linear regression (GLM) model adjusted for the gravidity, urine iodine, and TPOAb status was applied to assess the effects of IMH on adverse pregnancy outcomes, compared to the controls group.

RESULTS

Penalized logistic regression analysis indicated that the adjusted odds ratio (aOR) of Preterm premature rupture of the membranes (PPROM) in women with IMH was 5.43-folder higher than euthyroid group [aOR 5.43, 95% CI (1.40, 21.1), p = 0.01]. Besides, the adjusted odds ratio of low birth weight (LBW) in the IMH group was 2.53-folder higher than the healthy group [aOR 2.53, 95% CI (1.01, 6.33), p = 0.047]. Furthermore, the results of the GLM adjusted model revealed that the mean of neonatal head circumference and weight in the IMH group was around 0.43 cm (95% CI - 0.80, - 0.07, p = 0.02) and 145.4 g (95% CI - 242.6, - 48.1, p = 0.003) lower than euthyroid group, respectively.

CONCLUSIONS

This study demonstrated that women with IMH identified in early pregnancy have a higher odds ratio for developing some adverse pregnancy outcomes, including PPROM and LBW compared to their euthyroid counterparts. Also, the neonatal head circumference and weight in the IMH group were lower than in the euthyroid group.

Maternal Perfluoroalkyl Substances, Thyroid Hormones, and DIO Genes: A Spanish Cross-sectional Study

Results of studies on perfluoroalkyl substances (PFASs) and thyroid hormones (THs) are heterogeneous, and the mechanisms underlying the action of PFASs to target THs have not been fully characterized. We examined the relation between first-trimester maternal PFAS and TH levels and the role played by polymorphisms in the iodothyronine deiodinase 1 (DIO1) and 2 (DIO2) genes in this association. Our sample comprised 919 pregnant Spanish women (recruitment = 2003-2008) with measurements of perfluorohexanesulfonic acid (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), thyroid-stimulating hormone (TSH), total triiodothyronine (TT3), and free thyroxine (FT4), and we genotyped for single-nucleotide polymorphisms in the DIO1 (rs2235544) and DIO2 (rs12885300) genes. We performed multivariate regression analyses between PFASs and THs and included the interaction term PFAS-genotypes in the models. PFHxS was associated with an increase in TSH (% change in outcome [95% CI] per 2-fold PFAS increase = 6.09 [-0.71, 13.4]), and PFOA and PFNA were associated with a decrease in TT3 (-7.17 [-13.5, -0.39] and -6.28 [-12.3, 0.12], respectively). We found stronger associations between PFOA, PFNA, and TT3 for DIO1-CC and DIO2-CT genotypes, although interaction p-values were not significant. In conclusion, this study found evidence of an inverse association between PFOA and TT3 levels. No clear effect modification by DIO enzyme genes was observed.

Laboratory characteristics analysis of the efficacy of levothyroxine on subclinical hypothyroidism during pregnancy: a single-center retrospective study

To reassess the efficacy of levothyroxine on subclinical hypothyroidism (SCH, 4.0 mIU/L ≤ TSH (thyroid stimulating hormone) <10 mIU/L with normal free T4) during pregnancy. 165 levothyroxine-treated pregnant women experiencing SCH were screened. And controls were randomly selected using euthyroidism (EU) women, matched by age, gravidity, and parity in the EU group (n = 660). We evaluated laboratory characteristics and pregnancy outcomes during follow-ups. Compared with the EU group, the SCH group displayed higher inadequate maternal gestational weight gain, premature delivery, low birth weight offspring and infant offspring small for their gestational age. After levothyroxine treatment, the SCH group displayed lower total cholesterol, low-density lipoprotein levels, and higher serum homocysteine levels before delivery. Pregnant women with SCH still exhibit adverse pregnancy outcomes after levothyroxine treatment. Taken together, we believe that besides levothyroxine, vitamin B12 and folic acid could be added to the treatment of pregnant women with SCH. In addition, regular monitoring of blood sugar levels, lipid and homocysteine levels, and intervention gestational weight gain could alleviate the adverse effects of SCH on pregnancy outcomes.

Preconception Thyrotropin Levels and Risk of Adverse Pregnancy Outcomes in Chinese Women Aged 20 to 49 Years

IMPORTANCE

Maternal thyrotropin levels during gestation have a profound effect on pregnancy outcomes; however, few studies to date have evaluated the importance of preconception thyrotropin levels.

OBJECTIVE

To investigate the associations between preconception thyrotropin levels and pregnancy outcomes.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study enrolled Chinese women aged 20 to 49 years from the National Free Prepregnancy Checkups Project in China. Participants conceived within 6 months after the thyrotropin examination and completed follow-up for pregnancy outcomes between January 1, 2013, and December 31, 2017. Data were analyzed between May 1, 2019, and March 31, 2020.

EXPOSURES

Levels of thyrotropin within 6 months before pregnancy, measured as less than 0.10 mIU/L, 0.10 to 0.36 mIU/L, 0.37 to 2.49 mIU/L, 2.50 to 4.87 mIU/L, 4.88 to 9.99 mIU/L, and 10.00 mIU/L or greater.

MAIN OUTCOMES AND MEASURES

The association of maternal preconception thyrotropin levels with the 4 primary adverse pregnancy outcomes was assessed, including preterm birth (PTB), small for gestational age (SGA), birth defect, and perinatal infant death. Logistic regression analyses were used to evaluate the association between preconception maternal thyrotropin levels and risk of adverse pregnancy outcomes. The dose-response associations were assessed using restricted cubic spline regression.

RESULTS

This study enrolled 5 840 894 women (mean [SD] age, 26.30 [4.10] years) in the primary analysis. The median (interquartile range [IQR]) thyrotropin level was 1.60 (1.06-2.37) mIU/L. The cumulative incidences for the adverse pregnancy outcomes were as follows: PTB, 6.56%; SGA, 7.21%; birth defect, 0.02%; and perinatal infant death, 0.33%. Compared with the reference group (thyrotropin range, 0.37-2.49 mIU/L), both low (<0.10 mIU/L and 0.10-0.36 mIU/L) and high (4.88-9.99 mIU/L and ≥10.00 mIU/L) maternal preconception thyrotropin levels were associated with higher risk of PTB (low: odds ratio [OR], 1.23 [95% CI, 1.19-1.27] and OR, 1.15 [95% CI, 1.13-1.18] vs high: OR, 1.13 [95% CI, 1.10-1.15] and OR, 1.14 [95% CI, 1.08-1.20]), SGA (low: OR, 1.37 [95% CI, 1.33-1.40] and OR, 1.14 [95% CI, 1.12-1.17] vs high: OR, 1.05 [95% CI, 1.03-1.08] and OR, 1.17 [95% CI, 1.11-1.23]), and perinatal infant death (low: OR, 1.26 [95% CI, 1.10-1.43] and OR, 1.14 [95% CI, 1.05-1.24] vs high: OR, 1.31 [95% CI, 1.20-1.43] and OR, 1.47 [95% CI, 1.21-1.80]). J-shaped associations between preconception thyrotropin levels and PTB (χ2 = 1033.45; nonlinear P < .001), SGA (χ2 = 568.90; nonlinear P < .001), and perinatal infant death (χ2 = 38.91; nonlinear P < .001) were identified.

CONCLUSIONS AND RELEVANCE

In this cohort study, both low and high maternal thyrotropin levels were associated with a significantly increased risk of adverse pregnancy outcomes. Results suggest that the optimal preconception thyrotropin levels may be between 0.37 mIU/L and 2.50 mIU/L to prevent adverse pregnancy outcomes.

Impact of maternal thyroid hormone in late pregnancy on adverse birth outcomes: A retrospective cohort study in China

The purpose of this study was to explore the impact of maternal thyroid hormone dysfunction in late pregnancy on birth outcomes in a Chinese population. We retrospectively examined hospitalisation records and laboratory data between April 2016 and March 2017 and obtained results from 11,564 consecutive pregnant women with singleton births in which serum thyroid hormone had been examined together with birth outcomes. We assessed the association between maternal thyroid level and dysfunction with adverse birth outcomes based on regression analysis. Hyperthyroidism was associated with an increased risk of preterm birth (PTB, adjusted OR: 2.41, 95% CI: 1.83-3.17) and hypothyroidism was associated with an increased risk of small for gestational age (SGA, adjusted OR: 1.56, 95% CI: 1.10-2.22), while hyperthyroxinaemia was associated with a decreased risk of large for gestational age (LGA, adjusted OR: 0.64, 95% CI: 0.45-0.90). In addition, compared to women with normal FT3 and TSH (≥the 5^th and ≤the 95^th percentiles), women with high free triiodothyronine (FT3 >the 95^th percentile) and low thyroid-stimulating hormone (TSH <the 95^th percentile) had a 4.02- fold higher risk of PTB (95% CI: 2.05-7.88), and women with low FT3 and high TSH had a 4.22- fold greater risk of SGA (95% CI: 1.59-11.23). Our study supports associations between multiple types of maternal thyroid dysfunction in late pregnancy and adverse birth outcomes.

Do maternal urinary iodine concentration or thyroid hormones within the normal range during pregnancy affect growth parameters at birth? A systematic review and meta-analysis

CONTEXT

Iodine, an essential constituent of thyroid hormones, is required for proper growth and development.

OBJECTIVE

To investigate whether growth parameters at birth are associated with maternal urinary iodine concentration (UIC) or normal ranges of thyroid hormones during pregnancy.

DATA SOURCES

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, electronic databases (namely, MEDLINE, Web of Science, the Cochrane Library, Scopus, and Google Scholar) were searched between January 1988 and November 2018 to identify relevant articles.

DATA EXTRACTION

Data from the studies included were independently extracted by 2 investigators using standardized forms developed for this review.

DATA ANALYSIS

The pooled mean birth weight, length, and head circumference values, and 95% confidence intervals were estimated in newborns born to women with UIC < 150 and UIC ≥150 μg/L during pregnancy. Possible linear or nonlinear associations between maternal UIC and the aforementioned anthropometric measures were evaluated. A narrative synthesis of the data was performed for thyroid hormones with levels within the normal range.

RESULTS

Of the 123 studies identified, 11 were eligible for inclusion in the meta-analysis. The pooled mean birth weight, length, and head circumference in newborns whose mothers had UIC < 150 μg/L vs UIC ≥150 μg/L were 2898 g vs 2900 g (P = 0.970), 49.6 cm vs 49.4 cm (P = 0.880), and 34.0 cm vs 34.1 cm (P = 0.933), respectively. Dose-response meta-analyses revealed no significant linear or nonlinear associations between maternal UIC during pregnancy and anthropometric measures at birth. Among the different thyroid function parameters evaluated, high-normal values of maternal free thyroxine and thyrotropin during pregnancy were inversely associated with neonatal birth weight.

CONCLUSION

This systematic review showed that birth weight may be affected by even mild variations in the normal concentrations of maternal thyroid hormones. However, in the current meta-analysis, birth anthropometric measures were not associated with maternal UIC during pregnancy.

Relationship between Thyroid Status during the First Trimester of Pregnancy and Neonatal Well-Being

Iodine is an essential micronutrient for the synthesis of thyroid hormones. The proper functioning of the thyroid axis is essential for the normal development of the nervous system, especially in the first trimester of gestation. The aim of the present study was to analyze the perinatal outcomes, anthropometry, and APGAR test scores of newborns and to relate them to maternal thyroid status. A total of 190 newborns participated in the study. No correlation was found between thyroid stimulating hormone (TSH) and maternal ioduria values in the first trimester of gestation with the weight or length of the newborn, or the APGAR score at one minute after birth. However, we found significant differences between the APGAR scores of children whose mothers had an iodine sufficiency level in the first trimester compared to the children of mothers with iodine deficiency. Similarly, the APGAR scores of children whose mothers had a TSH > 4 have significantly better APGAR scores than the children of mothers with a TSH < 4. Likewise, we found significant differences between the measurements of the newborns depending on whether their mothers smoked. The children of mothers who took iodine supplements or iodized salt obtained the highest APGAR score at one and five minutes after birth. It is essential to focus on recommending adequate consumption of iodine supplements and iodized salt prior to gestation and at least during the first trimester to achieve better fetal well-being.

Prenatal and Postpartum Maternal Iodide Intake from Diet and Supplements, Urinary Iodine and Thyroid Hormone Concentrations in a Region of the United Kingdom with Mild-to-Moderate Iodine Deficiency

Iodine is essential for normal thyroid function, supporting healthy fetal and child development. Iodine requirements increase in pregnancy, but many women in regions without salt iodization have insufficient intakes. We explored associations between iodide intake and urinary iodine concentration (UIC), urinary iodine/creatinine ratio (I/Cr), thyroid stimulating hormone, thyroglobulin, free triiodothyronine, free thyroxine and palpable goiter in a region of mild-to-moderate iodine insufficiency. A total of 246 pregnant women aged 18–40 in Bradford, UK, joined the Health and Iodine in Babies (Hiba) study. They provided detailed information on diet and supplement use, urine and serum samples and were assessed for goiter at around 12, 26 and 36 weeks’ gestation, and 6, 18 and 30 weeks postpartum. Dietary iodide intake from food and drink was estimated using six 24 h recalls. During pregnancy, median (IQR) dietary iodide intake was 101 µg/day (54, 142), with 42% from dairy and 9% from white fish. Including supplements, intake was 143 µg/day (94, 196), with 49% < UK reference nutrient intake (140 µg/day). Women with Pakistani heritage had 129 µg/day (87, 190) median total intake. Total intake during pregnancy was associated with 4% (95% CI: 1%, 7%) higher UIC, 5% (3%, 7%) higher I/Cr, 4% (2%, 6%) lower thyroglobulin and 21% (9%, 32%) lower odds of palpable goiter per 50 µg/day. This cohort consumed less iodide in pregnancy than UK and World Health Organization dietary recommendations. UIC, I/Cr and thyroglobulin were associated with intake. Higher intake was associated with fewer goiters. Because dairy was the dominant source of iodide, women following plant-based or low-dairy diets may be at particular risk of iodine insufficiency.

Isolated maternal hypothyroxinemia and adverse pregnancy outcomes: A systematic review

Maternal thyroid hormones are vital for a normal pregnancy and the development of fetus and childhood; inadequate availability of thyroid hormones during pregnancy is associated with adverse pregnancy outcomes. Isolated maternal hypothyroxinemia (IMH) is defined as a low maternal T4 in the absence of TSH elevation. This systematic review aimed to investigate the association between IMH and adverse pregnancy outcomes. PubMed, Scopus and Web of science were searched for retrieving observational studies published up to September 2020, investigating the association of IMH with adverse pregnancy outcomes. From a total of 308 articles, 17 met our eligibility criteria and were used for the purpose of the present study. Definition of IMH varied in different studies. While some studies reported no adverse pregnancy outcomes for IMH, other studies found a positive association between first trimester IMH and feto-maternal outcomes including gestational hypertension, gestational diabetes, preterm delivery, fetal distress, small for gestational age, musculoskeletal malformations, spontaneous abortion, placental abruption and macrosomia. IMH, identified in the second trimester was associated with an increase in the risk of gestational diabetes, and hypertensive disorders of pregnancy in one study. There is no consensus on the adverse effects of IMH on pregnancy outcomes. Further comprehensive cohort studies using one standard definition for IMH, with large sample size and control of important confounders such as iodine status and maternal Thyroid peroxidase antibody (TPOAb) are needed for precise assessment of this association.

Quantifying the Impacts of Pre- and Post-Conception TSH Levels on Birth Outcomes: An Examination of Different Machine Learning Models

BACKGROUND

While previous studies identified risk factors for diverse pregnancy outcomes, traditional statistical methods had limited ability to quantify their impacts on birth outcomes precisely. We aimed to use a novel approach that applied different machine learning models to not only predict birth outcomes but systematically quantify the impacts of pre- and post-conception serum thyroid-stimulating hormone (TSH) levels and other predictive characteristics on birth outcomes.

METHODS

We used data from women who gave birth in Shanghai First Maternal and Infant Hospital from 2014 to 2015. We included 14,110 women with the measurement of preconception TSH in the first analysis and 3,428 out of 14,110 women with both pre- and post-conception TSH measurement in the second analysis. Synthetic Minority Over-sampling Technique (SMOTE) was applied to adjust the imbalance of outcomes. We randomly split (7:3) the data into a training set and a test set in both analyses. We compared Area Under Curve (AUC) for dichotomous outcomes and macro F1 score for categorical outcomes among four machine learning models, including logistic model, random forest model, XGBoost model, and multilayer neural network models to assess model performance. The model with the highest AUC or macro F1 score was used to quantify the importance of predictive features for adverse birth outcomes with the loss function algorithm.

RESULTS

The XGBoost model provided prominent advantages in terms of improved performance and prediction of polytomous variables. Predictive models with abnormal preconception TSH or not-well-controlled TSH, a novel indicator with pre- and post-conception TSH levels combined, provided the similar robust prediction for birth outcomes. The highest AUC of 98.7% happened in XGBoost model for predicting low Apgar score with not-well-controlled TSH adjusted. By loss function algorithm, we found that not-well-controlled TSH ranked 4^th, 6^th, and 7^th among 14 features, respectively, in predicting birthweight, induction, and preterm birth, and 3^rd among 19 features in predicting low Apgar score.

CONCLUSIONS

Our four machine learning models offered valid predictions of birth outcomes in women during pre- and post-conception. The predictive features panel suggested the combined TSH indicator (not-well-controlled TSH) could be a potentially competitive biomarker to predict adverse birth outcomes.

Thyroxine Supplementation in Pregnant Women After Thyroidectomy for Thyroid Cancer and Neonatal Birth Weight

Patients are often supplemented with a sufficient dose of thyroxine after thyroidectomy for thyroid cancer. However, the influence of thyroxine supplementation on fetal growth in pregnant women after thyroidectomy for thyroid cancer remains unclear. The aim of this study was to investigate the effect of thyroxine supplementation on neonatal birth weight. This cohort study included 49,896 pregnant women (278 patients with a history of thyroidectomy for thyroid cancer and 39,363 control cases after exclusion). Thyroid parameters were examined in pregnant women and their newborns. The associations between maternal thyroid function and neonatal birth weight and small for gestational age were studied using regression analyses. In the levothyroxine supplementation group, free thyroxine (FT4) levels were significantly higher in both early pregnancy (P < 0.001) and late pregnancy (P < 0.001) groups than in the control group. Furthermore, levels of neonatal thyroid stimulating hormone (P = 0.032) and birth weight (P = 0.043) were significantly lower than those in the control group. We also observed a significant inverse association between maternal FT4 levels in early pregnancy and neonatal birth weight (P=0.028), especially in male newborns (P=0.036). In summary, after thyroidectomy for thyroid cancer, a sufficient dose of thyroxine supplementation in early pregnancy is significantly associated with reduced birth weight and may need to be monitored.

Consequences of Iodine Deficiency and Excess in Pregnancy and Neonatal Outcomes: A Prospective Cohort Study in Rio de Janeiro, Brazil

Background: Insufficient or excessive iodine intake during gestation may compromise adaptive mechanisms in maternal thyroid function and lead to adverse pregnancy outcomes. In this context, we aimed to study the effects of maternal iodine status in the first and third trimesters of gestation on obstetric and neonatal outcomes in an iodine-sufficient population in Rio de Janeiro, Brazil. Methods: A total of 214 pregnant women in the first trimester of gestation were enrolled and prospectively followed until delivery between 2014 and 2017. All participants were ≥18 and ≤35 years, had a spontaneous single pregnancy, and had no history of thyroid or other chronic diseases, nor were they taking iodine-containing supplements at enrollment. In the first trimester, we obtained clinical information and determined thyroid function and the urinary iodine concentration (UIC) of the participants. Thyroid function and UIC were reassessed in the third trimester. Iodine status was determined by the median of UIC obtained from six urine spot samples by the inductively coupled plasma mass spectrometry method. Pregnancy and neonatal outcomes and delivery information were obtained from medical records. Results: The median UIC in the whole population was 219.7 μg/L. The prevalence of UIC <150 μg/L was 17.2%, and 38.7% had UIC ≥250 μg/L. Gestational diabetes (GDM) was higher in the group with UIC 250-499 μg/L (n = 77) compared with the group with UIC 150-249 μg/L (n = 94) (20.3% vs. 9.7%, p < 0.05). Ultimately, UIC ≥250 μg/L was an independent risk factors for GDM (relative risk [RR] = 2.9 [confidence interval, CI = 1.1-7.46], p = 0.027) and hypertensive disorders of pregnancy (HDP) (RR = 4.6 [CI = 1.1-18.0], p = 0.029). Among 196 live-born newborns, lower birth length was observed in infants whose mothers had UIC <150μg/L (n = 37) in the first trimester compared with those with UIC 150-249 μg/L (n = 86) (median interquartile range: 48.0 [2.2] vs. 49.0 [4.0] cm, p = 0.01). Maternal UIC <150 μg/L was negatively associated with birth length of newborns (Exp (B) = 0.33 [CI = 0.1-0.9], p = 0.03). Conclusions: In a population whose median iodine intake is sufficient, extensive individual variation occurs. Such abnormalities are associated with increased GDM and HDP when UIC is ≥250 μg/L, and lower infant birth length when UIC is <150 μg/L.

The Association Between Isolated Maternal Hypothyroxinemia in Early Pregnancy and Preterm Birth

Background: The association between isolated maternal hypothyroxinemia (IMH) during pregnancy and preterm birth (PTB), especially for subtypes of PTB, is unclear. This study aimed at determining the association between IMH diagnosed in early pregnancy and PTB, with further investigation into various subtypes of PTB. Methods: This study included 41,911 pregnant women (963 with IMH and 40,948 euthyroid women) who underwent first-trimester prenatal screening at the International Peace Maternity and Child Health Hospital (IPMCH) in Shanghai, China between January 2013 and December 2016. PTB was defined as birth before 37 weeks of gestation. PTB was further classified into three clinically relevant groups to investigate the clinical heterogeneity of PTB: (a) preterm birth with premature rupture of membranes (PROM-PTB); (b) spontaneous preterm birth with intact membranes (S-PTB); and (c) medically-induced preterm birth (MI-PTB). The overall and sex-specific effect of IMH on PTB and various subtypes of PTB were estimated by using logistic regression in crude and adjusted models. Results: Pregnant women with IMH had an increased risk of PTB (odds ratio [OR]: 1.32 [95% confidence interval; CI: 1.02-1.70], p = 0.03) compared with women with euthyroid function. The increased risk of PTB is mainly driven by S-PTB (OR: 1.57 [CI: 1.11-2.24], p = 0.01), while women with early pregnancy IMH had no statistically significant increased risk of PROM-PTB and MI-PTB. The effect of IMH on PTB was modified by fetal sex (p-values for interaction = 0.04). More prominent effects were observed in women carrying a female fetus, while no statistically significant effects were found in women carrying a male fetus. Conclusions: This study revealed that pregnant women with IMH in early pregnancy have a higher risk of PTB compared with euthyroid women. The effect of IMH on PTB is mainly driven by S-PTB and is modified by fetal sex.

Iodine status of pregnant women with obesity from inner city populations in the United Kingdom

BACKGROUND/OBJECTIVES

Iodine is essential for foetal neurodevelopment and growth. Requirements increase in pregnancy to support increased thyroid hormone synthesis for maternal and foetal requirements, and for foetal transfer. Iodine deficiency in pregnancy is widely reported, and obesity has been associated with sub-optimal thyroid function. We evaluated iodine status and its relation with birthweight in a secondary analysis of pregnant women with obesity from multi-ethnic inner-city settings who participated in the UK Pregnancies Better Eating and Activity trial (UPBEAT).

SUBJECTS/METHODS

Iodine and creatinine concentrations were evaluated in spot urine samples in the second (15⁺⁰-18⁺⁶ weeks, n = 954) trimester of pregnancy. We assessed iodine status as urinary iodine concentration (UIC) and urinary iodine-to-creatinine ratio (UI/Cr) and applied WHO/UNICEF/IGN population threshold of median UIC > 150 µg/L for iodine sufficiency. Relationships between iodine status and birthweight were determined using linear and logistic regression with appropriate adjustment, including for maternal BMI and gestational age.

RESULTS

Median (IQR) UIC and UI/Cr in the second trimester of pregnancy were 147 µg/L (99-257) and 97 µg/g (59-165), respectively. An UI/Cr <150 μg/g was observed in 70% of women. Compared to women with UI/Cr >150 µg/g, there was a trend for women with UI/Cr <150 µg/g to deliver infants with a lower birthweight (β = -60.0 g; 95% CI -120.9 to -1.01, P = 0.05).

CONCLUSIONS

Iodine status of pregnant women with obesity from this cohort of UK women was suboptimal. Lower iodine status was associated with lower birthweight.

Maternal Urinary Iodine Concentration and Pregnancy Outcomes in Euthyroid Pregnant Women: a Systematic Review and Meta-analysis

Iodine is an essential macronutrient for feto-maternal growth and development. Emerging evidence suggests that maternal iodine deficiency during pregnancy is potentially associated with both maternal and fetal adverse outcomes. The aim of this systematic review and meta-analysis was to investigate the association between maternal iodine status in euthyroid pregnant women and adverse pregnancy outcomes. A comprehensive literature search was performed in PubMed, Web of Science and Scopus up to October 2019 for retrieving related published articles in English. World Health Organization maternal median urinary iodine concentration (UIC) classification was used as follows: median UIC of less than 100, 100-149, 150-249, and more than 250 μg/L, for moderate-to-severe iodine deficiency, mild iodine deficiency, iodine adequate and more than adequate-to-excessive iodine, respectively. The primary outcomes of interest in this meta-analysis were the pooled prevalence and pooled odds ratio of the preterm birth, low birth weight (LBW), and one composite outcome of hypertensive disorders of pregnancy comprising pregnancy hypertension and preeclampsia. The secondary outcome was pooled mean of neonatal characteristics including birth weight, head circumference, Apgar score, and gestational age at birth. A total of 6 studies involving 7698 participants were included in this meta-analysis. The pooled prevalence of preterm birth, LBW, and hypertensive disorders of pregnancy were not statistically significantly different in the four groups of UIC levels. The pooled prevalence of preterm birth was 0.05, 0.04, 0.04, and 0.03 in UIC < 100, 100-149, 150-249, and > 250 μg/L, respectively. No evidence of an association was observed among the odds of preterm birth, LBW, and hypertensive disorders of pregnancy in euthyroid pregnant women with UIC between 100 and 149, 150-249, and > 250 μg/L compared with UCI < 100 μg/L. Likewise, there were not any statistical significant differences between the neonatal characteristics in different UIC groups. The results remained unchanged after subgroup analysis based on UIC less than 150 μg/L as abnormal UIC level. The present meta-analysis showed that the UIC of euthyroid pregnant women is not generally associated with the pregnancy outcomes and it per se is an insufficient indicator for prediction of pregnancy complications. The results of this study are important for reproductive healthcare providers and policymakers in providing appropriate healthcare service for pregnant women. However, further studies are needed to confirm these findings.

Impact of Dietary Habit, Iodine Supplementation and Smoking Habit on Urinary Iodine Concentration During Pregnancy in a Catalonia Population

(1) Background: The nutritional status of women during pregnancy can have a considerable effect on maternal and fetal health, and on the perinatal outcome. Aim: to assess the changes occurring in dietary iodine intake, potassium iodide supplementation, and smoking habit, and the impact of these changes on the urinary iodine concentration (UIC) during pregnancy in a population of women in Catalonia (Spain). (2) Methods: Between 2009–2011, an observational study included a cohort of women whose pregnancies were monitored in the public health system in the Central and North Metropolitan areas of Catalonia. Women received individual educational counseling, a dietary questionnaire was completed, and a urine sample was collected for iodine determination at each trimester visit. (3) Results: 633 (67.9%) women answered the questionnaire at all 3 visits. The percentage of women with a desirable UIC (≥150 μg/L) increased from the first to the second trimester and remained stable in the third (57.3%, 68.9%, 68%; p < 0.001). Analysis of the relationship between UIC ≥ 150 μg/L and the women’s dietary habits showed that the percentage with UIC ≥ 150 μg/L increased with greater consumption of milk in the first trimester, and the same was true for iodized salt use in all three trimesters and iodine supplementation in all three. (4) Conclusion: During pregnancy, increased intake of milk, iodized salt, and iodine supplements were associated with an increase in the UIC.

Insufficient maternal iodine intake is associated with subfecundity, reduced foetal growth, and adverse pregnancy outcomes in the Norwegian Mother, Father and Child Cohort Study

BACKGROUND

Severe iodine deficiency impacts fertility and reproductive outcomes. The potential effects of mild-to-moderate iodine deficiency are not well known. The aim of this study was to examine whether iodine intake was associated with subfecundity (i.e. > 12 months trying to get pregnant), foetal growth, and adverse pregnancy outcomes in a mild-to-moderately iodine-deficient population.

METHODS

We used the Norwegian Mother, Father and Child Cohort Study (MoBa) and included 78,318 pregnancies with data on iodine intake and pregnancy outcomes. Iodine intake was calculated using an extensive food frequency questionnaire in mid-pregnancy. In addition, urinary iodine concentration was available in a subsample of 2795 pregnancies. Associations were modelled continuously by multivariable regression controlling for a range of confounding factors.

RESULTS

The median iodine intake from food was 121 μg/day and the median urinary iodine was 69 μg/L, confirming mild-to-moderate iodine deficiency. In non-users of iodine supplements (n = 49,187), low iodine intake (< 100-150 μg/day) was associated with increased risk of preeclampsia (aOR = 1.14 (95% CI 1.08, 1.22) at 75 vs. 100 μg/day, p overall < 0.001), preterm delivery before gestational week 37 (aOR = 1.10 (1.04, 1.16) at 75 vs. 100 μg/day, p overall = 0.003), and reduced foetal growth (- 0.08 SD (- 0.10, - 0.06) difference in birth weight z-score at 75 vs. 150 μg/day, p overall < 0.001), but not with early preterm delivery or intrauterine death. In planned pregnancies (n = 56,416), having an iodine intake lower than ~ 100 μg/day was associated with increased prevalence of subfecundity (aOR = 1.05 (1.01, 1.09) at 75 μg/day vs. 100 μg/day, p overall = 0.005). Long-term iodine supplement use (initiated before pregnancy) was associated with increased foetal growth (+ 0.05 SD (0.03, 0.07) on birth weight z-score, p < 0.001) and reduced risk of preeclampsia (aOR 0.85 (0.74, 0.98), p = 0.022), but not with the other adverse pregnancy outcomes. Urinary iodine concentration was not associated with any of the dichotomous outcomes, but positively associated with foetal growth (n = 2795, p overall = 0.017).

CONCLUSIONS

This study shows that a low iodine intake was associated with restricted foetal growth and a higher prevalence of preeclampsia in these mild-to-moderately iodine-deficient women. Results also indicated increased risk of subfecundity and preterm delivery. Initiating iodine supplement use in pregnancy may be too late.

Maternal iodine status, intrauterine growth, birth outcomes and congenital anomalies in a UK birth cohort

BACKGROUND

Severe iodine insufficiency in pregnancy has significant consequences, but there is inadequate evidence to indicate what constitutes mild or moderate insufficiency, in terms of observed detrimental effects on pregnancy or birth outcomes. A limited number of studies have examined iodine status and birth outcomes, finding inconsistent evidence for specific outcomes.

METHODS

Maternal iodine status was estimated from spot urine samples collected at 26-28 weeks' gestation from 6971 mothers in the Born in Bradford birth cohort. Associations with outcomes were examined for both urinary iodine concentration (UIC) and iodine-to-creatinine ratio (I:Cr). Outcomes assessed included customised birthweight (primary outcome), birthweight, small for gestational age (SGA), low birthweight, head circumference and APGAR score.

RESULTS

There was a small positive association between I:Cr and birthweight in adjusted analyses. For a typical participant, the predicted birthweight centile at the 25th percentile of I:Cr (59 μg/g) was 2.7 percentage points lower than that at the 75th percentile of I:Cr (121 μg/g) (99% confidence interval (CI) 0.8 to 4.6), birthweight was predicted to be 41 g lower (99% CI 13 to 69) and the predicted probability of SGA was 1.9 percentage points higher (99% CI 0.0 to 3.7). There was no evidence of associations using UIC or other birth outcomes, including stillbirth, preterm birth, ultrasound growth measures or congenital anomalies.

CONCLUSION

Lower maternal iodine status was associated with lower birthweight and greater probability of SGA. Whilst small, the effect size for lower iodine on birthweight is comparable to environmental tobacco smoke exposure. Iodine insufficiency is avoidable, and strategies to avoid deficiency in women of reproductive age should be considered.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03552341. Registered on June 11, 2018.

Association of maternal thyroid function with birthweight: a systematic review and individual-participant data meta-analysis

BACKGROUND

Adequate transplacental passage of maternal thyroid hormone is important for normal fetal growth and development. Maternal overt hypothyroidism and hyperthyroidism are associated with low birthweight, but important knowledge gaps remain regarding the effect of subclinical thyroid function test abnormalities on birthweight-both in general and during the late second and third trimester of pregnancy. The aim of this study was to examine associations of maternal thyroid function with birthweight.

METHODS

In this systematic review and individual-participant data meta-analysis, we searched MEDLINE (Ovid), Embase, Web of Science, the Cochrane Central Register of Controlled Trials, and Google Scholar from inception to Oct 15, 2019, for prospective cohort studies with data on maternal thyroid function during pregnancy and birthweight, and we issued open invitations to identify study authors to join the Consortium on Thyroid and Pregnancy. We excluded participants with multiple pregnancies, in-vitro fertilisation, pre-existing thyroid disease or thyroid medication usage, miscarriages, and stillbirths. The main outcomes assessed were small for gestational age (SGA) neonates, large for gestational age neonates, and newborn birthweight. We analysed individual-participant data using mixed-effects regression models adjusting for maternal age, BMI, ethnicity, smoking, parity, gestational age at blood sampling, fetal sex, and gestational age at birth. The study protocol was pre-registered at the International Prospective Register of Systematic Reviews, CRD42016043496.

FINDINGS

We identified 2526 published reports, from which 36 cohorts met the inclusion criteria. The study authors for 15 of these cohorts agreed to participate, and five more unpublished datasets were added, giving a study population of 48 145 mother-child pairs after exclusions, of whom 1275 (3·1%) had subclinical hypothyroidism (increased thyroid stimulating hormone [TSH] with normal free thyroxine [FT4]) and 929 (2·2%) had isolated hypothyroxinaemia (decreased FT4 with normal TSH). Maternal subclinical hypothyroidism was associated with a higher risk of SGA than was euthyroidism (11·8% vs 10·0%; adjusted risk difference 2·43%, 95% CI 0·43 to 4·81; odds ratio [OR] 1·24, 1·04 to 1·48; p=0·015) and lower mean birthweight (mean difference -38 g, -61 to -15; p=0·0015), with a higher effect estimate for measurement in the third trimester than in the first or second. Isolated hypothyroxinaemia was associated with a lower risk of SGA than was euthyroidism (7·3% vs 10·0%, adjusted risk difference -2·91, -4·49 to -0·88; OR 0·70, 0·55 to 0·91; p=0·0073) and higher mean birthweight (mean difference 45 g, 18 to 73; p=0·0012). Each 1 SD increase in maternal TSH concentration was associated with a 6 g lower birthweight (-10 to -2; p=0·0030), with higher effect estimates in women who were thyroid peroxidase antibody positive than for women who were negative (pinteraction=0·10). Each 1 SD increase in FT4 concentration was associated with a 21 g lower birthweight (-25 to -17; p<0·0001), with a higher effect estimate for measurement in the third trimester than the first or second.

INTERPRETATION

Maternal subclinical hypothyroidism in pregnancy is associated with a higher risk of SGA and lower birthweight, whereas isolated hypothyroxinaemia is associated with lower risk of SGA and higher birthweight. There was an inverse, dose-response association of maternal TSH and FT4 (even within the normal range) with birthweight. These results advance our understanding of the complex relationships between maternal thyroid function and fetal outcomes, and they should prompt careful consideration of potential risks and benefits of levothyroxine therapy during pregnancy.

FUNDING

Netherlands Organization for Scientific Research (grant 401.16.020).

Effect of maternal active smoking during pregnancy on the trajectory of childhood body mass index: A multilevel analysis using quartiles of birthweight

INTRODUCTION

Maternal active smoking during pregnancy is associated with childhood obesity; however, whether maternal active smoking affects childhood body mass index (BMI) according to birthweight has not been examined.

METHODS

The study participants were 1955 women and their single-born infants, born between 1 April 1991 and 31 March 2003, in Koshu City, Japan, for whom complete data for birthweight, pre-pregnancy maternal BMI and pregnancy smoking status were available. Maternal smoking status during pregnancy was recorded using a questionnaire at the time of pregnancy registration. Childhood BMI was estimated by the BMI z-score, established by the World Health Organisation. Birthweight quartiles were grouped by sex and parity (first vs second or higher). Multilevel analysis, including both the individual and time as different level variables by each birthweight quartile, was used to describe the trajectories of BMI z-scores for statistical analyses.

RESULTS

In every quartile group, although children born to smoking mothers were leaner at birth, their BMI z-score increased around the age of 3 years. These children were larger than children born to non-smoking mothers. Significant interactions between maternal active smoking during pregnancy and child’s age were seen in those in the first and second quartiles of birthweight. Moreover, rapid growth in infancy was observed in the second quartile of birthweight.

CONCLUSIONS

The effect of maternal active smoking during pregnancy on childhood growth was more apparent among children in the second quartile of birthweight.

Hypothyroidism and isolated hypothyroxinemia in pregnancy, from physiology to the clinic

Many changes occur in the physiology of the maternal thyroid gland to maintain an adequate level of thyroid hormones (THs) at each stage of gestation during normal pregnancy, however, some factors can produce low levels of these hormones, which can alter the onset and progression of pregnancy. Deficiency of THs can be moderate or severe, and classified as overt or clinical hypothyroidism, subclinical hypothyroidism, and isolated hypothyroxinemia. Overt hypothyroidism has been reported in 0.3-1.9% and subclinical hypothyroidism in approximately 1.5-5% of pregnancies. With respect to isolated hypothyroxinemia, the frequency has been reported in approximately 1.3% of pregnant women, however it can be as high as 25.4%. Worldwide, iodine deficiency is the most common cause of hypothyroidism, however, in iodine-sufficient countries like the United States, the most common cause is autoimmune thyroiditis or Hashimoto's thyroiditis. The diagnosis and timely treatment of deficiency of THs (before or during the first weeks of gestation) can significantly reduce some of the related adverse effects, such as recurrent pregnancy loss, preterm delivery, gestational hypertension, and alterations in the offspring. However, so far there is no consensus on the reference levels of thyroid hormones during pregnancy to establish the diagnosis and there is no consensus on universal screening of women during first trimester of pregnancy to identify thyroid dysfunction, to give treatment and to reduce adverse perinatal events, so it is necessary to carry out specific studies for each population that provide information about it.

Association between infertility treatment and intrauterine growth: a multilevel analysis in a retrospective cohort study

OBJECTIVES

This study aimed to identify intrauterine growth differences according to infertility treatment compared with spontaneous conception and to describe intrauterine growth trajectories.

DESIGN

Retrospective cohort study.

SETTING

A single primary and tertiary medical centre in Japan.

PARTICIPANTS

This study included singleton pregnant women with prenatal check-ups and delivery at the University of Yamanashi Hospital between 1 July 2012 and 30 September 2017. Patients were divided into four groups: spontaneous conception, infertility treatment without assisted reproductive technology (ART), fresh-embryo transfer and frozen embryo transfer (FET).

INTERVENTIONS

Differences in intrauterine growth according to the infertility treatment, including ART, and birth weight were evaluated. Multilevel analysis was employed to evaluate intrauterine growth trajectories stratified by the sex of the offspring.

PRIMARY OUTCOME MEASURE

Estimated fetal weight (EFW) assessed by ultrasound examination.

RESULTS

We assessed data from 37 239 prenatal examination results from 2377 pregnant women (spontaneous conception, n=1764; infertility treatment without ART, n=171; fresh-embryo transfer, n=112; and FET, n=330) in the final analysis. Multilevel analysis was adjusted for gestation duration, gestation period, parity, hypertensive disorders of pregnancy, type of infertility treatment, maternal age, smoking status, placenta previa, thyroid disease, gestational diabetes mellitus and the interaction between each potential confounding factor and gestation duration. In male fetuses, the interaction between FET and gestational duration (estimate: 0.36; 95% CI: 0.06 to 0.67) significantly affected the EFW. Similarly, in female fetuses, FET (estimate: -69.85; 95% CI: -112.09 to -27.61) and the interaction between FET and gestation duration (estimate: 0.57; 95% CI: 0.28 to 0.87) significantly affected the EFW.

CONCLUSIONS

This study shows that FET affects intrauterine growth trajectory from the second trimester to term, particularly in female fetuses. Our findings require further prospective research to examine the effect of infertility treatment on fetal growth.

Maternal Urinary Iodine Concentration and Pregnancy Outcomes: Tehran Thyroid and Pregnancy Study

Iodine is essential for the production of thyroid hormones, and its deficiency during pregnancy may be associated with poor obstetric outcomes. The aim of this study was to investigate the relationship between maternal iodine statuses with pregnancy outcomes among pregnant Iranian women, considering their baseline thyrotropin (TSH) status. We used data from the Tehran Thyroid and Pregnancy Study (TTPS), a two-phase population-based study carried out among pregnant women receiving prenatal care. By excluding participants with overt thyroid dysfunction and those receiving levothyroxine, the remaining participants (n = 1286) were categorized into four groups, according to their urine iodine status: group 1, urine iodine concentration (UIC) < 100 μg/L; group 2, UIC between 100 and 150 μg/L; group 3, UIC between 150 and 250 μg/L; and group 4, UIC ≥ 250 μg/L. Primary outcome was preterm delivery. Preterm delivery occurred in 29 (9%), 19 (7%), 15 (5%), and 8 (4%) women, and neonatal admission was documented in 22 (7%), 30 (12%), 28 (11%), and 6 (3%) women of groups 1, 2, 3, and 4, respectively. Generalized linear regression model (GLM) demonstrated that the odds ratio of preterm delivery was significantly higher in women with urinary iodine < 100 μg/L and TSH ≥ 4 μIU/mL than those with similar urinary iodine with TSH < 4 μIU/mL (OR 2.5 [95% CI 1.1, 10], p = 0.024). Adverse pregnancy outcomes are increased among women with UIC < 100 μg/L, with serum TSH concentrations ≥ 4 μIU/mL.

Iodine Status, Thyroid Function, and Birthweight: A Complex Relationship in High-Risk Pregnancies

(1) Background: The consequences of iodine deficiency and/or thyroid dysfunction during pregnancy have been extensively studied, emphasizing on infant neurodevelopment. However, the available information about the relationship between iodine, thyroid hormones, and fetal growth in high-risk pregnancies is limited. We aim to investigate if iodine metabolism and/or thyroid parameters can be affected by adverse antenatal/perinatal conditions. (2) Methods: A cross-sectional study examined differences in iodine status, thyroid function, and birthweight between high-risk (HR group; n = 108)) and low-risk pregnancies (LR group; n = 233) at the time of birth. Urinary iodine concentration (UIC), iodine levels in amniotic fluid, and thyroid parameters [thyroid-stimulating hormone (TSH), free thyroxine (FT4)] were measured in mother–baby pairs. (3) Results: There were significant differences between HR and LR groups, free thyroxine (FT4) concentration in cord blood was significantly higher in the LR group compared with HR pregnancies (17.06 pmol/L vs. 15.30 pmol/L, respectively; p < 0.001), meanwhile iodine concentration in amniotic fluid was significantly lower (13.11 µg/L vs. 19.65 µg/L, respectively; p < 0.001). (4) Conclusions: Our findings support the hypothesis that an adverse intrauterine environment can compromise the availability of FT4 in cord blood as well as the iodine metabolism in the fetus. These differences are more noticeable in preterm and/or small fetuses.

Insignificant Effect of Isolated Hypothyroxinemia on Pregnancy Outcomes During the First and Second Trimester of Pregnancy

Objective: Adverse maternal outcomes and perinatal complications are associated with overt and subclinical maternal hypothyroidism. It is not clear whether these complications also occur in women with isolated hypothyroxinemia during pregnancy. The aim of this study was to evaluate the effects of isolated hypothyroxinemia on maternal and perinatal outcomes during pregnancy. Methods: This study included data from 2,864 pregnant women in the first trimester (67 women with isolated hypothyroxinemia, 784 euthyroid women) and the second trimester (70 women with isolated hypothyroxinemia, 1,943 euthyroid women) of pregnancy. Maternal serum samples were collected in the first and second trimesters to examine thyroid hormone concentration. Hypothyroxinemia was defined as a normal maternal thyroid-stimulating hormone concentration with a low maternal free thyroxine concentration and negative thyroid autoantibodies. The following maternal outcomes were recorded: gestational hypertension, gestational diabetes mellitus, placenta previa, placental abruption, prelabor rupture of membranes, and premature delivery. Perinatal outcomes, including fetal growth restriction, fetal distress, low birth weight, intrauterine fetal death, and malformation. The incidence of adverse pregnancy outcomes and perinatal complications was compared between women in the first trimester and second trimester with isolated hypothyroxinemia. Results: There were no significant differences in the incidence rates of adverse maternal outcomes and perinatal complications between patients in the first and second trimesters with isolated hypothyroxinemia. Conclusion: The results of this study indicate that isolated hypothyroidism does not increase the incidence of adverse maternal outcomes and perinatal complications.

Neonatal Screening for Congenital Hypothyroidism: What Can We Learn From Discordant Twins?

CONTEXT

Newborn screening program for congenital hypothyroidism (CH) adopting rescreening in at-risk neonates.

OBJECTIVES

To estimate the concordance rate for CH in twin pairs discordant at the first screening; to verify whether long-term follow-up of healthy cotwins belonging to CH discordant pairs may be useful to diagnose thyroid hypofunction during development; to evaluate the importance of genetic and environmental influences on liability to permanent and transient CH.

DESIGN AND PATIENTS

Forty-seven screening discordant twin pairs were investigated. Proband was defined as the twin in the pair with a positive test at the first screening and a confirmed diagnosis of CH.

RESULTS

Seven screening discordant twin pairs became concordant for CH within the first month of life (pairwise concordance of 14.9%) because seven screening negative cotwins showed high TSH values when retested. During long-term follow-up (range, 3 to 21 years), hypothyroidism was diagnosed in two monozygotic screening negative cotwins at the age of 9 months and 12 years, respectively. Furthermore, the twin analysis showed that 95% of liability to transient CH was explained by genetic factors and 5% by environmental (unshared) factors, whereas 64% of phenotypic variance of permanent CH was explained by common environmental factors (shared during the fetal life) and 36% by unshared environmental factors.

CONCLUSIONS

This study showed that the introduction of rescreening permits the diagnosis of CH in a greater number of twins. It also showed the importance of long-term follow-up in both twins in the pair, and the role of nongenetic factors in the etiology of permanent CH.

Association Between Maternal Thyroid Hormones and Birth Weight at Early and Late Pregnancy

CONTEXT

Previous studies suggest that maternal thyroid function affects fetal growth, but the association between combined thyroid hormones from early to late pregnancy and newborn birth weight remains unknown.

OBJECTIVE

To explore the association of maternal thyroid function during early and late pregnancy with birth weight.

DESIGN

A large prospective cohort study of a Chinese population.

SETTING

This study recruited pregnant women who underwent first-trimester prenatal screenings at the International Peace Maternity and Child Health Hospital between January 2013 and December 2016.

PARTICIPANTS

This study enrolled 46,186 mothers in whom TSH, free thyroxine (FT4), T3, and thyroid peroxidase antibody concentrations were measured in the first and third trimesters and in whom data on birth weight were available.

MAIN OUTCOME MEASURES

Birth weight, small for gestational age, large for gestational age (LGA).

RESULTS

A higher TSH or FT4 concentration, or a lower T3 concentration, during the first or third trimester was associated with a lower birth weight. The lowest percentiles of maternal FT4 (FT4 < 2.5th percentile) in both trimesters were associated with a 0.34-SD higher birth weight. The effect estimates were greater in those in the first trimester (0.23 SD) or in the third trimester (0.17 SD). The association of maternal TSH and FT4 with birth weight differed according to fetal sex.

CONCLUSIONS

Persistently low FT4 concentrations throughout pregnancy were associated with higher birth weight and an increased risk of LGA. Based on these findings, we recommend monitoring mildly altered concentrations of thyroid hormone throughout pregnancy.

Maternal Heavy Metal Exposure, Thyroid Hormones, and Birth Outcomes: A Prospective Cohort Study

CONTEXT

Maternal thyroid hormones during pregnancy play a critical role in fetal development. However, whether maternal heavy metal exposure affects their thyroid hormones and the effects on fetal growth are still unclear.

OBJECTIVE

To explore the effect of heavy metal exposure on maternal thyroid hormones and the potential mediation role of thyroid hormones on birth outcomes.

METHODS

Concentrations of heavy metals in urine samples and thyroid hormones in blood samples of 675 pregnant women were measured during early pregnancy in a cohort study conducted in China. Multivariable linear regressions were applied to explore the associations of maternal urinary heavy metal levels with both maternal thyroid hormones and birth outcomes. Mediation analyses were performed to assess the mediation role of thyroid hormones in these associations.

RESULTS

Maternal urinary vanadium (V) exhibited an inverse association with free T3 (FT3) and FT3/free T4 (FT4) ratio levels. Urinary arsenic (As) and lead (Pb) had inverse relationships with FT3. We also observed the positive associations of maternal FT3 and FT3/FT4 ratio with birthweight. The mediation analyses suggested that 5.33% to 30.57% of the associations among V, As, and Pb levels and birth size might be mediated by maternal FT3 or FT3/FT4 ratio.

CONCLUSIONS

We have shown that maternal exposures to V, As, and Pb at early pregnancy were associated with decreased maternal FT3 or FT3/FT4 ratio, which might contribute to reduced birthweight. Mediation analyses indicated that maternal thyroid hormone was a possible mediator of the association between urinary heavy metals and birth size.

The Joint Role of Thyroid Function and Iodine Status on Risk of Preterm Birth and Small for Gestational Age: A Population-Based Nested Case-Control Study of Finnish Women

Normal maternal thyroid function during pregnancy is essential for fetal development and depends upon an adequate supply of iodine. Little is known about how iodine status is associated with preterm birth and small for gestational age (SGA) in mildly iodine insufficient populations. Our objective was to evaluate associations of early pregnancy serum iodine, thyroglobulin (Tg), and thyroid-stimulating hormone (TSH) with odds of preterm birth and SGA in a prospective, population-based, nested case-control study from all births in Finland (2012–2013). Cases of preterm birth (n = 208) and SGA (n = 209) were randomly chosen from among all singleton births. Controls were randomly chosen from among singleton births that were not preterm (n = 242) or SGA (n = 241) infants during the same time period. Women provided blood samples at 10–14 weeks’ gestation for serum iodide, Tg and TSH measurement. We used logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for preterm birth and SGA. Each log-unit increase in serum iodide was associated with higher odds of preterm birth (adjusted OR = 1.19, 95% CI = 1.02–1.40), but was not associated with SGA (adjusted OR = 1.01, 95% CI = 0.86–1.18). Tg was not associated with preterm birth (OR per 1 log-unit increase = 0.87, 95% CI = 0.73–1.05), but was inversely associated with SGA (OR per log-unit increase = 0.78, 95% CI = 0.65–0.94). Neither high nor low TSH (versus normal) were associated with either outcome. These findings suggest that among Finnish women, iodine status is not related to SGA, but higher serum iodide may be positively associated with preterm birth.