Subclinical Changes in Maternal Thyroid Function Parameters in Pregnancy and Fetal Growth

Association Between Maternal Thyroid Hormone Concentration with Normal Thyroid Function During Pregnancy and Preschoolers' Glycolipid Metabolism: A Birth Cohort Study

Background: Thyroid hormones (THs) are essential endocrine hormones that play key roles in individual's growth and development. There is limited knowledge about the association between maternal TH concentrations variations with normal thyroid function during pregnancy and offspring's glycolipid metabolism. Methods: A total of 1130 mother-child pairs from the Ma'anshan birth cohort were included in this prospective study. Maternal TH levels and thyroid peroxidase antibodies were measured in the 1st, 2nd, and 3rd trimesters of pregnancy during the childhood follow-up period. Fasting venous blood was collected from children at 4-6 years of age and glycolipid metabolic indicators were assayed. Analyses were performed using Binary logistic regression models, linear regression models, and Generalized linear regression model. Results: Maternal TH trajectories were fitted via latent category growth models. During the 1st trimester of pregnancy, maternal T3 and free thyroxine (fT4) levels were positively associated with children's blood glucose levels (β = 0.007 [CI 0.028-0.181]; β = 0.022 [CI 0.004-0.040]), whereas high levels of fT4 may be associated with decreased risk of children's hypercholesterolemia (OR = 0.870 [CI 0.768-0.986]). Maternal T4 concentrations during the 3rd trimester of pregnancy were negatively associated with children's cholesterol levels (β = -0.002 [CI -0.003-0.00]). High maternal TH levels were associated with high fasting glucose level and low low-density lipoprotein concentrations in children. Conclusions: Maternal TH dynamic variations may be associated with glycolipid metabolism in preschoolers, even when women do not have clinically diagnosed thyroid disorders. The exact associations between maternal THs in specific trimesters of pregnancy under normal thyroid function conditions and glycolipid metabolism in offspring require further investigation.

Physiological and Microbial Community Dynamics in Does During Mid-Gestation to Lactation and Their Impact on the Growth, Immune Function, and Microbiome Transmission of Offspring Kids

This study investigated changes in physiological processes and rumen microbial communities in does from mid-gestation to lactation and identified potential associations between these physiological changes and the rumen microbiome. Additionally, we studied the transmission mechanisms of microorganisms between the dam and offspring. Our study demonstrates significant changes in maternal physiological metabolism, immune status, and rumen microbiota from mid-pregnancy through lactation. We identified potential associations between these physiological changes and the rumen microbiome. Moreover, the findings highlight that alterations in maternal physiological metabolism and immune status significantly influence the growth and immune development of offspring kids. Additionally, we observed that the maternal microbiota serves as a key source of gastrointestinal microbial communities in young animals, with early colonization of maternally derived microbes in the offspring's gastrointestinal tract playing a role in shaping their immune system development. The results for primary outcomes are as follows: The serum levels of estrogen and progesterone in pregnant does were greater than those observed during lactation, while the concentration of growth hormone, triiodothyronine, and glucose exhibited an upward trend during lactation. During late gestation, the serum IL-10 concentration in does decreased, while the TNF-α concentration increased. Additionally, on day 140 of gestation, does showed a significant decrease in IgG, total protein, and globulin levels. From mid-gestation to lactation, the abundance of dominant phyla and genera, including Firmicutes, Bacteroidetes, Patescibacteria, Bacteroidales_RF16_group, Clostridia_UCG-014, RF39, and Eubacterium_ventriosum_group, in the rumen of does underwent significant changes. LEfSe analysis identified a series of marker microorganisms in the rumen of does at different physiological stages. A correlation was observed between these dominant bacteria and the serum physiological indicators of the does. Notably, rumen volatile fatty acids also exhibited a correlation with serum physiological indicators. In addition, serum physiological indicators of does were significantly correlated with the growth and immune indicators of their kids. Microbiological origin analysis revealed that the gastrointestinal microbiome of kids primarily originated from the rumen, birth canal, and milk of does. Further analysis identified a correlation between the kids' serum immunometric indicators and certain gastrointestinal microorganisms. In particular, the jejunum microbiota of 28-day-old lactating kids, including Alysiella, Neisseria, and Muribaculaceae, showed a significant positive correlation with serum IL-6 and IL-10 levels. Meanwhile, these genera were dominant in the saliva and milk of does, suggesting a direct microbial transfer from dam to offspring. These microbial communities may play a significant role in modulating the metabolism and immune responses of the offspring, thereby influencing their immune system development.

Outdoor light at night exposure was associated with hypothyroidism in pregnant women: A national study in China

BACKGROUND

Evidence on the influence of outdoor artificial light at night (ALAN) on hypothyroidism in pregnant women is scarce. We aimed to investigate the association between outdoor ALAN exposure and hypothyroidism in pregnancy.

METHODS

81,820 pregnant women from the China Birth Cohort Study (CBCS) were analyzed, which recruited from 18 provinces and autonomous regions in China between February 2018 and December 2020. Hypothyroidism was defined based on clinical diagnosis by physicians. Outdoor ALAN exposure (nW/cm2/sr) within 1500 m was estimated using VIIRS/DNB satellite data based on the participants' residential address. The Outdoor ALAN was divided in quartiles, with the lowest quartile (Q1) serving as the reference group. Generalized linear mixed models were employed to estimate the association between ALAN exposure and hypothyroidism.

RESULTS

Among the 81,120 pregnant women, 3902 (4.77 %) were diagnosed hypothyroidism. Pregnant women with hypothyroidism had significantly higher median (IQR, interquartile range) outdoor ALAN levels during pregnancy compared to those without hypothyroidism (30.97 (18.15) vs. 29.14 (20.21) nW/cm2/sr, p < 0.01). After adjusting for covariates, we found that each quartile increment of outdoor ALAN exposure was associated with an adjusted Odds Ratio (aOR of 1.15 (95 % Confidence Interval [95 % CI]: 1.03-1.27), 1.15 (1.05-1.28), and 1.12 (1.00-1.25) for hypothyroidism, respectively from Q2 to Q4. Additionally, stratified analyses revealed that pre-pregnancy BMI was a significant modifier in the association between outdoor ALAN and hypothyroidism in pregnancy, with stronger effects observed among those who were overweight before pregnancy (1.21 [95 % CI, 1.05-1.39] vs. 1.03 [95 % CI, 0.97-1.10], p for interaction = 0.01).

CONCLUSIONS

Outdoor ALAN exposure is positively associated with hypothyroidism in pregnancy. To benefit maternal and infant health and well-being, recommendations for mitigating ALAN pollution and effective measures to avoid excessive light exposure should be developed.

Association between air pollutants, thyroid disorders, and thyroid hormone levels: a scoping review of epidemiological evidence

Background

Over the past two decades, the incidence of thyroid disorders has been steadily increasing. There is evidence to suggest that air pollution may be one of the etiological factors of thyroid diseases. This comprehensive review aimed to examine the evidence related to air pollutants and thyroid disorders and thyroid hormones levels from an epidemiological perspective.

Methods

The scoping review adopted a systematic approach to search for, identify, and include peer-reviewed articles published in English. We performed a comprehensive search of three databases-PubMed, Embase, and Web of Science to identify relevant literature on the relationship between air pollution [particulate matter, nitrogen oxide, carbon monoxide (CO), ozone (O3), sulfur dioxide (SO2)] exposure and thyroid disorders, including hypothyroidism, congenital hypothyroidism (CH), thyroid nodules, thyroid cancer, autoimmune thyroid diseases, as well as thyroid hormone levels, such as thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4). Articles published until August 1, 2023, were included.

Results

A total of 3,373 studies were retrieved, and among them, 25 studies covering eight different air pollutants were relevant. The most frequently studied air pollutants in this review included fine particulate matter (with fine particulate matter (PM2.5), n=21; inhalable particles (PM10), n=10; PM10-2.5, n=1) and nitrogen oxides (with NO2, n=13; NOx, n=3). The thyroid disorders and thyroid hormone levels most commonly associated with evidence of air pollution exposure were hypothyroidism (n=7) and TSH (n=12).

Conclusions

Despite variations in study designs and exposure assessments, the findings consistently highlight the substantial health risks that air pollution, particularly PM2.5, poses to thyroid health, especially among vulnerable populations. Given that our study was limited to epidemiological investigations and the increasing prevalence of toxic substances in the environment, there is an urgent need for further research to elucidate the mechanisms by which these pollutants disrupt thyroid function and contribute to the development of thyroid diseases.

Associations of urinary polycyclic aromatic hydrocarbon (PAH) metabolites and their mixture with thyroid hormone concentration during pregnancy in the LIFECODES cohort: A repeated measures study

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) are endocrine disruptors resulting from incomplete combustion. Pregnancy represents a particularly vulnerable period to such exposures, given the significant influence of hormone physiology on fetal growth and pregnancy outcomes. Maternal thyroid hormones play crucial roles in fetal development and pregnancy outcomes. However, limited studies have examined gestational PAH exposure and maternal thyroid hormones during pregnancy.

METHODS

Our study included 439 women enrolled in the LIFECODES birth cohort in Boston, aiming to explore the relationship between urinary PAH metabolites and thyroid hormones throughout pregnancy. Urine samples for PAH metabolite analysis and plasma samples for thyroid hormone were measured up to four visits throughout gestation. Single pollutant analyses employed linear mixed effect models to investigate individual associations between each PAH metabolite and thyroid hormone concentration. Sensitivity analyses were conducted to assess potential susceptibility windows and fetal-sex-specific effects of PAH exposure. Mixture analyses utilized quantile g-computation to evaluate the collective impact of eight PAH metabolites on thyroid hormone concentrations. Additionally, Bayesian kernel machine regression (BKMR) was employed to explore potential non-linear associations and interactions between PAH metabolites. Subject-specific random intercepts were incorporated to address intra-individual correlation of serial measurements over time in both single pollutant and mixture analyses.

RESULTS

Our findings revealed positive trends in associations between PAH metabolites and thyroid hormones, both individually and collectively as a mixture. Sensitivity analyses indicated that these associations were influenced by the study visit and fetal sex. Mixture analyses suggested non-linear relationships and interactions between different PAH exposures.

CONCLUSIONS

This comprehensive investigation underscores the critical importance of understanding the impact of PAH exposures on thyroid hormone physiology during pregnancy. The findings highlight the intricate interplay between environmental pollutants and human pregnancy physiology, emphasizing the need for targeted interventions and public health policies to mitigate adverse outcomes associated with prenatal PAH exposure.

Occurrence of rare earth elements in umbilical cord serum and association with thyroid hormones and birth outcomes in newborns

Rare earth elements (REEs) are emerging contaminants that are increasingly used in high technology products. However, limited information is available regarding exposure to REEs and associated health effects in neonates. This study aimed to investigate the association between REE concentrations and thyroid hormone levels, as well as birth outcomes in 109 newborns in Beijing, China. We measured the concentrations of 16 REEs and thyroid hormones in umbilical cord serum. To assess the impact of exposure to individual REEs and REE mixtures on thyroid hormone levels and birth outcomes, we employed univariate linear regression, least absolute shrinkage and selection operator (LASSO), and weighted quantile sum (WQS) models. We detected 14 REEs at high rates (92.6%-100%), with yttrium exhibiting the highest median (interquartile range) concentration [43.94 (0.33-172.55) ng/mL], followed by scandium [3.64 (0.46-11.15) ng/mL]. Univariate analyses showed that per logarithmic (ln)-unit change of neodymium (Nd) and samarium (Sm) was associated with 0.039 [95% confidence interval (CI): 0.001, 0.007] and 0.031 (95% CI: 0.003, 0.060) increases in free thyroxine (FT4) levels, respectively. Moreover, 14 REEs exhibited significant associations with triiodothyronine (T3) levels, resulting in increases ranging from 0.066 to 0.307. Elevated concentrations of terbium (Tb) [per ln-unit change: -0.021 (95% CI: -0.041, -0.01)] and lutetium (Lu) [-0.023 (95% CI: -0.043, -0.002)] were inversely correlated with birth length in newborns. A further multiple exposure analysis employing the LASSO model identified Sm, Nd, Y, Sc, and Lu as critical factors influencing FT4 and T3 levels. Additionally, WQS analyses showed positive associations between exposure to a mixture of 14 REEs and FT4 (P = 0.046), T3 (P < 0.001), and birth length (P = 0.049). These findings suggest that in utero exposure to REEs might disrupt thyroid hormone homeostasis and impact intrauterine growth. Further studies are warranted to validate these findings and elucidate the underlying mechanisms.

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.

Associations of cord serum polybrominated diphenyl ether (PBDE) mixture with birth outcomes and mediating role of thyroid function: Evidence from the Sheyang Mini Birth Cohort Study

BACKGROUND

Polybrominated diphenyl ethers (PBDEs), a series of worldwide applied flame retardants, may influence fetal growth and interfere with thyroid function. The study intended to explore the relationship between in-utero exposure to PBDE mixture and newborn anthropometric indexes and to further examine the potential mediating role of thyroid function.

METHODS

Demographics and laboratory measures of 924 mother-infant pairs were obtained from the database of the Sheyang Mini Birth Cohort Study. We applied gas chromatography-mass spectrometry (GC-MS) and electrochemiluminescence immunoassay to measure nine PBDE congeners and seven thyroid function parameters in umbilical cord serum samples, respectively. We fitted generalized linear models and Bayesian kernel machine regression (BKMR) to evaluate associations of lipid-adjusted cord serum PBDEs, as individuals and as a mixture, with newborn anthropometric and cord serum thyroid function parameters. We applied causal mediation analysis to test our hypothesis that thyroid function parameters act as a mediator between PBDEs and birth outcomes.

RESULTS

The molarity of cord serum ∑9PBDE had a median value of 31.23 nmol/g lipid (IQR 19.14 nmol/g lipid, 54.77 nmol/g lipid). BDE-209 was the most dominant congener. Birth length was positively associated with both single exposure to BDE-28 and cumulative exposure to PBDEs. Correspondingly, ponderal index (PI) was negatively associated with BDE-28 and the total effects of PBDE mixture. Free triiodothyronine had a negative trend with BDE-209 and PBDE mixture. In the sex-stratified analysis, BDE-153 concentrations were positively correlated with PI among males (β = 0.03; 95%CI: 0.01, 0.05; P = 0.01) but not among females. Cord serum thyrotropin mediated 14.92% of the estimated effect of BDE-153 on PI.

CONCLUSIONS

In-utero mixture exposure to PBDEs was associated with birth outcomes and thyroid function. Thyroid function might act as a mediator in the process in which PBDEs impact the growth of the fetus.

Association of vitamin A with gestational diabetes and thyroid disorders in pregnancy and their influence on maternal, fetal, and neonatal outcomes

Gestational diabetes mellitus (GDM) and thyroid disorders during pregnancy pose significant health concerns, impacting a substantial number of mothers globally. Globally, about 14% of pregnant women develop GDM, while thyroid disorders impact approximately 2%-3%. Both conditions contribute to adverse outcomes, including gestational hypertension, excessive fetal growth, and heightened perinatal morbidity. The central focus of this literature review is to examine the relationship between vitamin A, a crucial fat-soluble micronutrient in fetal development, and the occurrence of GDM and thyroid disorders during pregnancy. The primary research question investigates the association between vitamin A, GDM, and thyroid disorders, analyzing their combined impact on maternal, fetal, and neonatal outcomes. The review underscores the potential of vitamin A to modulate the risk and outcomes of GDM and thyroid disorders during gestation, emphasizing its role in GDM development and resolution and its influence on thyroid function in pregnancy.

[Association of maternal isolated thyroid peroxidase antibody positive in the first trimester with fetal growth]

OBJECTIVE

To investigate the association of isolated thyroid peroxidase antibody (TPOAb) positive in the first trimester with fetal growth.

METHODS

A total of 16 446 pregnant women were included in the birth cohort study, whose last menstrual period was between May 2016 and April 2019 and with singleton pregnancy. Maternal serum samples were collected when they firstly came for prenatal care in the first trimester. The pregnant women were consecutively seen and followed in the hospital and the information of pregnant women was extracted from the electronic medical information system. The pregnant women were divided into isolated TPOAb positive group (n=1 654) and euthyroid group (n=14 792). Three fetal ultrasound examinations were scheduled during the routine prenatal visits at the hospital and were performed by trained sonographers. All fetal growth indicators were quantified as gestational age- and gender- adjusted standard deviation score (Z-score) using the generalized additive models for location, scale and shape (GAMLSS). Fetal growth indicators included estimated fetal weight (EFW), abdominal circumference (AC), biparietal diameter (BPD), femur length (FL) and head circumference (HC). Fetal growth restriction (FGR) was defined as AC or EFW Z-score＜3rd centile based on clinical consensus. Generalized estimating equation (GEE) analysis was applied to assess the association of maternal isolated TPOAb positive with fetal growth. The generalized linear model was further used to analyze the association between isolated TPOAb positive and fetal growth indicator at different gestational ages when the fetal growth indicator was significantly associated with isolated TPOAb positive in the GEE mo-del.

RESULTS

The median gestational age at three ultrasound measurements was 23.6 (23.3, 24.1), 30.3 (29.7, 30.9), 37.3 (37.0, 37.7) weeks, respectively. The BPD Z-score was higher in isolated TPOAb positive women, compared with the euthyroid pregnant women after adjustment (β=0.057, 95%CI: 0.014-0.100, P=0.009). The generalized linear model showed the BPD Z-score was higher in the isolated TPOAb positive women at the end of 21-25 weeks (β=0.052, 95%CI: 0.001-0.103, P=0.044), 29-32 weeks (β=0.055, 95%CI: 0.004-0.107, P=0.035) and 36-40 weeks (β=0.068, 95%CI: 0.011-0.125, P=0.020), compared with the euthyroid pregnant women. There was no difference in other fetal growth indicators (EFW, AC, FL and HC) and FGR between the isolated TPOAb positive and euthyroid pregnant women.

CONCLUSION

The BPD Z-score was slightly increased in the isolated TPOAb positive pregnant women in the first trimester, while other fetal growth indicators were not changed. The reproducibility and practical significance of this result need to be confirmed.

Polycyclic aromatic hydrocarbon (PAH) exposure during pregnancy and child anthropometry from birth to 10 years of age: Sex-specific evidence from a cohort study in rural Bangladesh

Polycyclic aromatic hydrocarbons (PAHs) have endocrine disrupting properties and they cross the placental barrier, but studies on gestational exposure and child anthropometry are inconclusive. We aimed to elucidate the impact of early gestational PAH exposure on anthropometry from birth to 10 years of age in 1295 mother-child pairs from a nested sub-cohort of the MINIMat trial in Bangladesh. Several PAH metabolites [1-hydroxyphenanthrene (1-OH-Phe), Σ2-,3-hydroxyphenanthrene (Σ2-,3-OH-Phe), 4-hydroxyphenanthrene (4-OH-Phe), 1-hydroxypyrene (1-OH-Pyr), Σ2-,3-hydroxyfluorene (Σ2-,3-OH-Flu)] were quantified in spot urine collected around gestational week 8 using LC-MS/MS. Child weight and height were measured at 19 occasions from birth to 10 years. Multivariable-adjusted regression models were used to assess associations of maternal PAH metabolites (log₂-transformed) with child anthropometry. The median concentration of 1-OH-Phe, Σ2-,3-OH-Phe, 4-OH-Phe, 1-OH-Pyr and Σ2-,3-OH-Flu was 1.5, 1.9, 0.14, 2.5, and 2.0 ng/mL, respectively. All maternal urinary PAH metabolites were positively associated with newborn weight and length and all associations were more pronounced in boys than in girls (p interaction for all <0.14). In boys, the strongest associations were observed with Σ2-,3-OH-Phe and Σ2-,3-OH-Flu for which each doubling increased mean birth weight by 41 g (95% CI: 13; 69 and 12; 70) and length by 0.23 cm (0.075; 0.39) and 0.21 cm (0.045; 0.37), respectively. Maternal urinary PAH metabolites were not associated with child anthropometry at 10 years. In longitudinal analysis, however, maternal urinary PAH metabolites were positively associated with boys' weight-for-age (WAZ) and height-for-age Z-scores (HAZ) from birth to 10 years, but only the association of 4-OH-Phe with HAZ was significant (B: 0.080 Z-scores; 95% CI 0.013, 0.15). No associations were observed with girls' WAZ or HAZ. In conclusion, gestational PAH exposure was positively associated with fetal and early childhood growth, especially in boys. Further studies are needed to confirm causality and to explore long-term health effects.

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.

Effect of levothyroxine treatment on fetal growth among women with mild subclinical hypothyroidism and thyroid peroxidase antibody negative: a cohort study

BACKGROUND

Some clinicians used levothyroxine (LT4) treatment for mild subclinical hypothyroidism (SCH) pregnant women (2.5 < thyroid-stimulating hormone (TSH) ≤ the pregnancy-specific reference range with normal free thyroxine (FT4) level) with thyroid peroxidase antibody negative (TPOAb^-), although the recent clinical guideline did not recommend it. It is unknown whether LT4 treatment for pregnant women with mild SCH and TPOAb^- have impact on fetal growth. Therefore, the aim of the study was to investigate the effect of LT4 treatment on fetal growth and birth weight among mild SCH pregnant women with TPOAb^-.

METHODS

This was a birth cohort study including 14,609 pregnant women between 2016 and 2019 in Tongzhou Maternal and Child Health Hospital of Beijing, China. Pregnant women were divided into 3 groups as follows: Euthyroid (n = 14,285, 0.03 ≤ TSH ≤ 2.5mIU/L, normal FT4), TPOAb^-; Untreated mild SCH with TPOAb^- (n = 248, 2.5 < TSH ≤ 2.9mIU/L, normal FT4, without LT4 treatment); Treated mild SCH with TPOAb^- (n = 76, 2.5 < TSH ≤ 2.9mIU/L, normal FT4, with LT4 treatment). The main outcome measures were Z-scores of fetal growth indicators (abdominal circumference (AC), biparietal diameter (BPD), femur length (FL), head circumference (HC), estimated fetal weight (EFW)), fetal growth restriction (FGR) and birth weight.

RESULTS

There was no difference in fetal growth indicators and birth weight between the untreated mild SCH women with TPOAb^- and the euthyroid pregnant women. But the HC Z-score was lower in the LT4 treated mild SCH women with TPOAb^-, compared with the euthyroid pregnant women (β = -0.223, 95%CI: -0.422, -0.023). The LT4 treated mild SCH women with TPOAb^- had lower fetal HC Z-score (β = -0.236, 95%CI: -0.457, -0.015), compared with the untreated mild SCH women with TPOAb^-.

CONCLUSIONS

We observed that LT4 treatment for mild SCH with TPOAb^- was associated with decreased fetal HC, which was not observed for untreated mild SCH women with TPOAb^-. The adverse effect of LT4 treatment for mild SCH with TPOAb^- provided new evidence for the recent clinical guideline.

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.

Maternal Thyroid Function and Birth Weight in Twins

CONTEXT

Thyroid hormones are associated with birth weight in singleton pregnancy. Twin pregnancies need more thyroid hormones to maintain the normal growth and development of the fetuses compared with single pregnancy.

OBJECTIVE

We aimed to investigate the association of thyroid hormones and birth weight in twins.

METHODS

This was a retrospective cohort study in a Chinese population. Pregnant women who received regular antenatal health care and delivered live-born twins from 2014 to 2019 were included (n = 1626). Linear mixed model with restricted cubic splines and logistic regression models were used to estimate the association of thyroid hormones with birth weight and birth weight discordance in twins.

RESULTS

We observed that both thyrotropin (TSH) and free thyroxine (FT4) were not associated with birth weight in twins overall, while when stratifying on fetal sex or chorionicity, there were nonlinear association between FT4 levels and birth weight in boys (Pnonlinear < .001) and in dichorionic (DC) twins (Pnonlinear = 0.03). Women with levels of FT4 lower than the 10th percentile had a higher risk of birth weight discordance in their offspring than women with normal FT4 levels (range, 2.5 to 97.5 percentiles) (odds ratio = 1.58; 95% CI, 1.05-2.33).

CONCLUSION

Our study suggests there was an association of FT4, but not TSH, with birth weight and birth weight discordance varied by sex and chorionicity. These findings could have implications for obstetricians to be aware of the importance of FT4 levels in preventing birth weight discordance in twin pregnancy.

Association of maternal thyroid dysfunction and autoimmunity with adverse birth outcomes

This study aimed to explore the relationship between thyroid function and autoimmunity and adverse birth outcomes. Serum levels of thyroid function were detected by electrochemiluminescence assay. Urine iodine concentration was detected using the acid digestion method. We used multiple linear regression to assess the correlation between thyroid function indicators and birth weight according to trimester stratification and binary logistic regression to evaluate the correlation between thyroid dysfunction and adverse birth outcomes. Reference ranges for trimester-specific thyroid hormones were established in our 2564 pregnant women cohort with mild iodine deficiency. The higher the maternal thyroid-stimulating hormone in the first trimester (B = 0.09, P = 0.048) and total triiodothyronine (TT3) in the third trimester (B = 0.16, P < 0.001) of TPOAbnegative women, the higher the birth weight Z-score, whereas in the second trimester, free-thyroxine of mothers with TPOAb negative was lower (B = -0.10, P = 0.026) and the birth weight Z-score was higher. Pregnant women with overt and subclinical hyperthyroidism had a higher risk of preterm births than euthyroid women (11.9% vs 4.5%; odds ratio (OR): 2.84; P = 0.009). Women with higher TT3 had a higher risk of preterm (17.0% vs 4.5%; OR: 4.19; P < 0.001) and LGA (34.0% vs 11.1%; OR: 3.70; P < 0.001) births than euthyroid women. In conclusion, thyroid function during pregnancy could affect birth weight and birth outcome.

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.

Maternal essential metals, thyroid hormones, and fetal growth: Association and mediation analyses in Chinese pregnant women

BACKGROUND

Essential metals play critical roles in fetal growth and development, but results from human studies are inconsistent. Additionally, whether maternal thyroid hormone (TH) levels mediate the associations between essential metals and fetal growth remains unknown.

METHODS

Data for analysis were extracted from the Information System of Guangdong Women and Children Hospital between January 2017 and December 2019. Maternal levels of essential metals [copper (Cu), zinc (Zn), magnesium (Mg), and iron (Fe)] and THs were measured at the second trimester. Multivariate linear models were introduced to evaluate the potential associations between maternal essential metals, thyroid functions, and fetal growth, and the possible mediation effects of thyroid functions were explored in the median analyses.

RESULTS

A total of 4186 mother-infant pairs were included in the present study. Maternal Fe levels were found to significantly increase birth weight in 272.91 g (95 % CI: 15.59, 530.22) among anemia group. Maternal Cu levels were positively associated with increased free triiodothyronine/free thyroxine ratio (FT3/FT4). Negative associations of Fe and Mg levels with thyroid-stimulating hormone (TSH) concentrations were observed, accompanied with the positive associations in relation to FT3, FT4 and FT3/FT4 ratio. Mediation analyses suggested that 72.01 % of the associations between Fe levels and birth length might be mediated by FT3 levels. Additionally, 25.85 % of the Cu-birth length association and 44.53 % of the Fe-birth length association could be explained by FT3/FT4 ratio.

CONCLUSION

Our findings suggest that maternal Cu, Mg, and Fe levels can alter TH concentrations, and maternal FT3 and FT3/FT4 ratio might be potential mediators on the developmental effects of Cu and Fe levels.

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.

Association of Thyroid Function with Suicidal Behavior: A Systematic Review and Meta-Analysis

Thyroid disease is a very common condition that influences the entire human body, including cognitive function and mental health. As a result, thyroid disease has been associated with multiple neuropsychiatric conditions. However, the relationship between thyroid dysfunction and suicide is still controversial. We conducted a systematic review and meta-analysis to describe the association of thyroid function with suicidal behavior in adults. We searched four data bases (MEDLINE, EMBASE, PsycINFO, and Scopus) from their inception to 20 July 2018. Studies that reported mean values and standard deviation (SD) of thyroid hormone levels [Thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), total thyroxine (TT4), and total triiodothyronine (TT3)] in patients with suicidal behavior compared with controls were included in this meta-analysis. The abstracts and papers retrieved with our search strategies were reviewed independently and in duplicate by four reviewers for assessment of inclusion criteria and data extraction, as well as for evaluation of risk of bias. Random-effects models were used in this meta-analysis to establish the mean difference on thyroid function tests between groups. Overall, 2278 articles were identified, and 13 studies met the inclusion criteria. These studies involved 2807 participants, including 826 participants identified with suicidal behavior. We found that patients with suicide behavior had lower levels of FT3 (-0.20 pg/mL; p = 0.02) and TT4 (-0.23 µg/dL; p = 0.045) compared to controls. We found no differences in either TSH, FT4, or TT3 levels among groups. With our search strategy, we did not identify studies with a comparison of overt/subclinical thyroid disease prevalence between patients with and without suicide behavior. The studies included in this meta-analysis had a low-to-moderate risk of bias. In the available literature, the evidence regarding the association of thyroid disorders and suicidal behavior is limited. We found that patients with suicidal behavior have significantly lower mean FT3 and TT4 levels when compared to patients without suicidal behavior. The clinical implications and pathophysiologic mechanisms of these differences remain unknown and further research is needed.

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.

The role of thyroid-stimulating hormone and thyroglobulin antibody in abnormally invasive placenta

PURPOSE

Thyroid hormones and antibodies are known to participate in angiogenesis and invasion and also thyroid hormone receptors are expressed in the placenta. We aimed to evaluate the relationship of serum levels of thyroid-stimulating hormone (TSH), thyroid hormones (TH), and anti-thyroid antibodies with abnormally invasive placenta (AIP). We also aimed to investigate whether they are related with cesarean hysterectomy and massive blood transfusion need in AIP cases.

METHODS

A total of 88 pregnant patients were enrolled in this prospective case-control study (30 with AIP, 28 with non-adherent placenta previa totalis (PPT) and 30 controls). Serum TSH, thyroid hormone [T3 (triiodothyronine) and T4 (thyroxine)] and thyroid antibodies against thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) levels were studied in maternal serum at initial admission to our Perinatology Unit (at early third trimester). The factors associated with increased risk of AIP, cesarean hysterectomy, massive blood transfusion, and adverse perinatal outcomes were evaluated with multiple logistic regression analysis. Adjusted odds ratios and 95% confidence intervals were also calculated.

RESULTS

Serum TSH and TgAb levels were significantly lower in the AIP group than both PPT and control groups (p = .01, p < .001 and p < .001, p < .001 respectively). Decreased serum levels of TSH (<2.16 mIU/L) and TgAb (<2.70 mIU/L) levels and high previous cesarean section rates were found to be independently associated with AIP in pregnant women with PPT (OR: 0.4, 95% CI: 0.1-0.9; p = .04, OR: 0.7, 95%CI: 0.4-1.3, p = .02 and OR: 0.1, 95% CI: 0.1-0.5, p = .01). Decreased serum TSH and TgAb levels were found to be independently associated with an increased rate of cesarean hysterectomy and massive blood transfusion in AIP cases (OR: 3.7, 95% CI: 1.4-9.8; p = .01, OR: 1.8, 95% CI: 1.1-3.1; p = .03 and OR: 2.6, 95% CI: 1.0-6.5; p = .05, OR: 2.2, 95% CI: 1.1-4.1 p = .02). Decreased TSH and TgAb serum levels were also found to be independently associated with adverse perinatal outcomes in AIP cases (OR: 3.4, 95% CI: 1.3-11.0; p = .01 and OR: 1.978, 95% CI: 2-3.6; p = .03).

CONCLUSION

Decreased serum TSH and TgAb levels, and previous history of cesarean section were all found to be significantly associated with AIP in cases with PPT. We suggest that maternal serum TSH and TgAb levels can provide additional contribution to obstetric Doppler ultrasound in the diagnosis of AIP and thus can reduce the risks of unplanned cesarean hysterectomy in cases with PPT.

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.

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 levothyroxine supplementation on pregnancy loss and preterm birth in women with subclinical hypothyroidism and thyroid autoimmunity: a systematic review and meta-analysis

BACKGROUND

Subclinical hypothyroidism (SCH) and thyroid autoimmunity (TAI) are associated with adverse pregnancy outcomes such as pregnancy loss and preterm birth. However, the ability of levothyroxine (LT4) supplementation to attenuate the risks of these outcomes remains controversial.

OBJECTIVE AND RATIONALE

This systematic review and meta-analysis was conducted to determine the effect of LT4 supplementation on pregnancy loss rate (PLR) and preterm birth rate (PBR) among pregnant women with SCH and TAI.

SEARCH METHODS

A systematic literature search of the PubMed, EMBASE, Web of Science and Cochrane Controlled Trials Register databases and Clinicaltrials.gov was performed to identify all relevant English studies published up to April 2018. The following terms were used for the search: [subclinical hypothyroidism OR thyroid autoimmunity OR thyroperoxidase antibody (TPO-Ab) OR thyroglobulin antibodies (Tg-Ab)] AND (levothyroxine OR euthyrox) AND [pregnancy outcome OR miscarriage OR abortion OR pregnancy loss OR preterm birth OR premature delivery OR early labo(u)r]. The reference lists of the relevant publications were also manually searched for related studies. Published manuscripts were included if they reported data on pregnancy loss, preterm birth or both. We separately analysed the pooled effects of LT4 supplementation on PLR and PBR in women with SCH and TAI.

OUTCOMES

Overall, 13 eligible studies including 7970 women were included in the meta-analysis. Eight and five of these studies were randomized controlled trials (RCTs) and retrospective studies, respectively. The pooled results indicated that LT4 supplementation significantly decreased the PLR [relative risk (RR) = 0.56, 95% confidence interval (CI): 0.42-0.75, I2 = 1%, 12 studies] and PBR (RR = 0.68, 95% CI: 0.51-0.91, I2 = 21%, eight studies) in women with SCH and/or TAI. We further found that LT4 supplementation significantly decreased the risk of pregnancy loss (RR = 0.43, 95% CI: 0.26-0.72, P = 0.001, I2 = 0%) but not of preterm birth (RR = 0.67, 95% CI: 0.41-1.12, P = 0.13, I2 = 0%) in women with SCH. Furthermore, LT4 supplementation significantly decreased the risks of both pregnancy loss (RR = 0.63, 95% CI: 0.45-0.89, P = 0.009, I2 = 0%) and preterm birth (RR = 0.68 95% CI: 0.48-0.98, P = 0.04, I2 = 46%) in women with TAI. These results were consistent when only RCTs were included in the analysis. Further, in women with SCH, LT4 supplementation reduced the risk of pregnancy loss in pregnancies achieved by assisted reproduction (RR = 0.27, 95% CI: 0.14-0.52, P < 0.001, I2 = 14%) but not in naturally conceived pregnancies (RR = 0.60, 95% CI: 0.28-1.30, P = 0.13, I2 = 0%). By contrast, in women with TAI, LT4 supplementation reduced the risks of both pregnancy loss (RR = 0.61, 95% CI: 0.39-0.96, P = 0.03, I2 = 0%) and preterm birth (RR = 0.49, 95% CI: 0.30-0.79, P = 0.003, I2 = 0%) in naturally conceived pregnancies but not in pregnancies achieved by assisted reproduction (RR = 0.68, 95% CI: 0.40-1.15, P = 0.15, I2 = 0% for pregnancy loss and RR = 1.20, 95% CI: 0.68-2.13, P = 0.53, I2 not applicable for preterm birth).

WIDER IMPLICATIONS

This meta-analysis confirmed the beneficial effects of LT4 supplementation, namely the reduced risks of pregnancy loss and preterm birth, among pregnant women with SCH and/or TAI. The different effects of LT4 supplementation on naturally conceived pregnancies and pregnancies achieved by assisted reproduction in women with SCH and/or TAI suggest that these women should be managed separately. Due to the limited number of studies included in this meta-analysis, especially in the subgroup analysis, further large RCTs and fundamental studies are warranted to confirm the conclusions and better clarify the molecular mechanism underlying these associations.

Study on subclinical hypothyroidism in pregnancy: a bibliometric analysis via CiteSpace

Background: Subclinical hypothyroidism (SCH) in pregnancy has drawn an increasing amount of attention over the past two decades. However, the definition of it, including its clinical diagnosis and treatment, is still being revised. An increased risk of adverse pregnancy outcomes have been shown in most but not all studies. The objective of this study was to evaluate the origin, current trend and research hotspots on SCH in pregnancy.Methods: We obtained 630 records with 12,033 references, published between 1999 and 2018, from the online version of SCI-Expanded, Thomson Reuters Web of Science. The CiteSpace 5.3.R4 was used to perform the cooperation network analysis, key words co-occurrence and burst detection analysis, and reference cocitation analysis.Results: We identified that the number of publications on SCH in pregnancy was increasing over the past two decades. Teng WP and Shan ZY from the First Hospital of China Medical University, Shenyang, China, were found to be the most productive researchers in this field. USA was the leading country for publications. Subclinical hypothyroidism, pregnancy, hypothyroidism, dysfunction, disease, management, women, deficiency, association and hyperthyroidism were the top 10 high frequency keywords in all recruit documents. Follow up was the most strength burst key word in this field from 1999 through 2018, followed by maternal hypothyroxinemia, child, hypothyroidism complicating pregnancy, antithyroid antibody and fetal. Moreover, cocitation reference analysis revealed the top landmark articles and clusters in this field.Conclusion: This study provides the trends and frontiers in the field of SCH in pregnancy and valuable information for endocrine and/or obstetric researchers to identify new perspectives on potential collaborators and cooperative countries.

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.

Effect of Gestational Weight Gain on Associations Between Maternal Thyroid Hormones and Birth Outcomes

Purpose: The aim was to investigate the associations between maternal thyroid parameters within the normal ranges during early pregnancy and birth outcomes, and further to examine whether the associations were modified by gestational weight gain (GWG). Methods: Maternal serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) concentrations within the normal ranges during early pregnancy were measured from 8,107 pregnant women in Wuhan, China. The associations between maternal thyroid parameters and birth outcomes (birth weight, birth length, and low birth weight) were analyzed using multivariable adjusted regression models, and effect modification by pre-pregnancy body mass index (BMI) category and GWG were further evaluated. Results: Maternal TSH and FT4 concentrations were negatively associated with birth weight, and the latter only occurred in normal weigh women with inadequate and excessive GWG, as well as in both underweight and overweight women with excessive GWG (e.g., β = -359.33 g, 95% CI: -700.95, -17.72 in underweight women with excessive GWG for per unit increase of FT4 concentrations). Moreover, maternal FT4 and FT3 concentrations were associated with increased risk for low birth weight, and the latter only occurred in normal weigh women with inadequate GWG (OR = 2.52, 95% CI: 1.00, 6.36 for per unit increase of FT3 concentrations). These associations still persist when maternal thyroid parameters were modeled as quintiles. Main conclusion: Maternal normal thyroid function during early pregnancy with excessive and inadequate GWG may adversely influence fetal growth.

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.

Subclinical hypothyroidism in pregnancy

PURPOSE OF REVIEW

Subclinical hypothyroidism (SCH) is a common diagnosis among women of reproductive age. The importance of sufficient maternal thyroid supply during pregnancy is well known. Nevertheless, the effects of SCH during pregnancy and the efficacy of its treatment on maternofetal outcomes are not well established. This review discusses the recent evidence on SCH in pregnancy and how this evidence is reflected in current clinical care.

RECENT FINDINGS

Recent observational studies have found a positive association between SCH during pregnancy and adverse maternal, neonatal and offspring outcomes, mainly in thyroid peroxidase autoantibody positive women. Although interventional studies have shown a benefit of levothyroxine (LT4) treatment on selected pregnancy outcomes, there was no effect on offspring neurodevelopment.

SUMMARY

Current evidence strengthens the association between SCH with both maternofetal and offspring adverse outcomes. An earlier and more individualized diagnostic assessment taking into consideration predictors of thyroid dysfunction and major risk factors for complications could result in better management of SCH during pregnancy. The effectiveness of LT4 on improving maternofetal and long-term offspring outcomes is still not fully elucidated.

Thyroid hormone concentrations in second trimester of gestation and birth outcomes in Shanghai, China

BACKGROUND

Previous studies suggested that thyroid function in the first trimester of gestation played an important role in fetal growth. However, limited clinical data are available to support this relationship in the second trimester of gestation.

OBJECTIVE

We examined the relationship of maternal thyroid function parameters in early second trimester of gestation with birth outcomes in China.

METHODS

Participating 5016 mother-infant pairs were recruited from the Songjiang District Maternity and Infant Hospital, Shanghai, China, between July and December 2016. Linear regression assessed the associations of thyroid hormones with birthweight. Logistic regression tested the correlations between thyroid hormones and low birthweight, macrosomia, small for gestational age , and large for gestational age infants. Maternal serum TSH, TT3, TT4, FT3, and FT4 concentrations were measured in 16-20 weeks of gestation.

RESULTS

TT3 and FT3 were positively associated with birthweight, while TT4 and FT4 were negatively associated with birthweight, respectively. Furthermore, higher TT3 and FT3 were associated with increased risks of LGA infants (OR = 1.48, 95% CI: 1.15-1.9; OR = 1.22, 95% CI: 1.01-1.46), respectively. Higher TT3 was associated with an increased risk of macrosomic infants (OR = 1.35, 95% CI: 1.04-1.74). In contrast, higher FT4 was associated with decreased risks of LGA (OR = 0.87, 95% CI: 0.81-0.93) and macrosomic infants (OR = 0.90, 95% CI: 0.84-0.96), respectively. No associations were found between TSH and any of the outcomes.

CONCLUSIONS

TT3 and FT3 were positively associated with fetal growth, while TT4 and FT4 were negatively associated with fetal growth. Our findings suggested that thyroid function in early second trimester of gestation is a potential risk factor for abnormal fetal growth.

[Thyroid disease in pregnancy : Review of current literature and guidelines]

Impaired thyroid function is observed in 15% of all pregnancies and thus represents a relevant clinical issue. The key recommendations of currents as well as a selection of recently published literature are presented in this review.