Iodine levels and thyroid hormones in healthy pregnant women and birth weight of their offspring

Association of maternal urinary pesticide metabolites with neonatal birth outcomes and the moderating effects of iodine

Previous studies have demonstrated the effects of prenatal pesticide exposure on birth outcomes. How to mitigate the harmful effects of pesticide exposure is of great practical significance. The micronutrient iodine is a cornerstone for the growth and development of newborns and throughout their lifespan. In this study, we investigated the association of urinary pesticide metabolite and urinary iodine concentrations with neonatal birth weight, birth length, and ponderal index in 781 mother-newborn pairs. The indirect role of urinary iodine in the associations between urinary pesticide metabolites and neonatal birth indicators was assessed by moderation analysis. The geometric mean concentration of total pesticide metabolites was 10.32 μg/L and the median urinary iodine concentration was 192.63 μg/L among the pregnant women. The mean birth length and birth weight of the newborns were 49.82 cm and 3186.94 g, respectively. Restricted cubic spline analysis revealed significant non-linear associations of 2,4-dichlorophenoxyacetic acid and Trans-dichlorovinyl-dimethylcyclopropane carboxylic acid with birth weight. The Bayesian kernel-machine regression analysis did not show a significant overall effect of mixed pesticide exposure on neonatal birth outcomes, suggesting that the effects of individual metabolites may be more critical than overall pesticide exposure. The moderation analysis results showed that the impact of pesticide metabolites on the ponderal index varied from a significant negative to a non-significant or significant positive correlation as urinary iodine concentrations increased. The results demonstrated that ensuring adequate iodine levels may help mitigate the adverse effects of pesticide exposure on birth outcomes.

Women with Autoimmune Thyroiditis Taking Levothyroxine During Pregnancy: Is Iodine Supplementation Needed?

BACKGROUND

Iodine is fundamental for the synthesis of thyroid hormones, which play a central role in foetal neurological development. The need for an iodine-containing supplement (ICS) in L-T4-treated women during pregnancy is still a subject of debate.

AIM OF THE STUDY

The aim of the study is to investigate the iodine status in women with autoimmune thyroiditis (AT) who have or have not been treated with L-T4.

METHODS

This was a cross-sectional, observational study involving pregnant women with AT, treated with/without L-T4. Upon enrolment, women provided a urine sample (to measure the urinary iodine concentration (UIC), which was normalised to urinary creatinine values (UI/Creat)), and completed a questionnaire. TSH, FT4, and neonatal TSH were also obtained.

RESULTS

Among women taking an ICS, 74.1% had a UI/Creat level ≥ 150 μg/g, compared with only 46.2% of those not taking an ICS (p = 0.03). Among L-T4 users only, a UI/Creat level ≥ 150 μg/g was more frequent in ICS users than in non-ICS users (72.8% vs. 41.7%) (p = 0.03). In the multivariate analysis, ICS use was the only independent variable for UI/Creat ≥ 150 μg/g (OR: 3.4; CI: 1.1-10.9) (p = 0.04). There was a tendency towards higher UI/Creat levels as the L-T4 (µg/Kg) dosage increased, although no correlation was found. Newborns of women taking an ICS were found to have elevated neonatal TSH (2.8 mIU/L vs. 1.7 mIU/L) (p = 0.04). All newborns with a TSH >5 mUI/L were those of women taking supplements.

CONCLUSIONS

Women with AT taking L-T4 still need iodine supplementation, although the amount should be regulated on the basis of their L-T4 dosage.

Maternal Thyroid Hormones as Mediators between Phthalate Exposure and Neonatal Birth Weight: A Cross-Sectional Study from the Zunyi Birth Cohort

Studies have shown that exposure to phthalates can affect neonatal birth weight. However, epidemiological evidence on the mediating role of maternal thyroid hormones is limited. Therefore, this study, based on the Compliance Birth Cohort, aimed to reveal the potential mediating function of maternal thyroid hormones during pregnancy between phthalic acid ester (PAE) exposure and neonatal birth weight. The study included 1274 mother-infant pairs. Linear regression analysis revealed a negative association between MIBP and neonatal birth weight (β = -62.236; 95% CI: -118.842, -5.631). Bayesian kernel-machine regression (BKMR) indicated a nonlinear negative association between PAE metabolites (PAEs) and birth weight. Linear regression analysis revealed a positive association between neonatal birth weight and FT3 (β = 41.605; 95% CI: 2.631, 80.380). The BKMR model also found a positive association between thyroid hormones and birth weight but in a nonlinear manner. Additionally, linear regression analyses showed that TSH, TT3, TT4, FT3, and FT4 were associated with PAEs. The BKMR model revealed an inverted U-shaped association of PAEs with TT3 and FT3 and a nonlinear association with TSH, TT4, and FT4. Structural equation modeling revealed that MMP, MIBP, MBP, MEHP, MOP, MBZP, and MEOHP contributed to a net reduction in neonatal birth weight of 32 g through the TT3, FT3, TT4, and FT4 pathways. The findings suggest that exposure to PAEs during pregnancy leads to a reduction in neonatal birth weight, possibly due to the involvement of maternal thyroid hormones as mediators. Controlling maternal thyroid hormone levels during pregnancy may be a viable method to reduce the harmful effects of phthalate exposure on the developing fetus.

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.

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.

Optimizing Growth: The Case for Iodine

Iodine is an essential micronutrient and component of thyroid hormone. An adequate dietary iodine intake is critical to maintain and promote normal growth and development, especially during vulnerable life stages such as pregnancy and early infancy. The role of iodine in cognitive development is supported by numerous interventional and observational studies, and when iodine intake is too low, somatic growth is also impaired. This can be clearly seen in cases of untreated congenital hypothyroidism related to severe iodine deficiency, which is characterized, in part, by a short stature. Nevertheless, the impact of a less severe iodine deficiency on growth, whether in utero or postnatal, is unclear. Robust studies examining the relationship between iodine and growth are rarely feasible, including the aspect of examining the effect of a single micronutrient on a process that is reliant on multiple nutrients for optimal success. Conversely, excessive iodine intake can affect thyroid function and the secretion of optimal thyroid hormone levels; however, whether this affects growth has not been examined. This narrative review outlines the mechanisms by which iodine contributes to the growth process from conception onwards, supported by evidence from human studies. It emphasizes the need for adequate iodine public health policies and their robust monitoring and surveillance, to ensure coverage for all population groups, particularly those at life stages vulnerable for growth. Finally, it summarizes the other micronutrients important to consider alongside iodine when seeking to assess the impact of iodine on somatic growth.

No Association Was Found Between Mild Iodine Deficiency During Pregnancy and Pregnancy Outcomes: a Follow-up Study Based on a Birth Registry

BACKGROUND

Severe iodine deficiency during gestation is associated with adverse pregnancy outcomes; however, the impact of mild-to-moderate iodine deficiency, though prevalent in pregnancy, remains unclear.

METHODS

We extracted follow-up data for 7435 pregnant women from a national iodine deficiency disorders monitoring program from 2016 to 2018 and a mother-child cohort study in 2017 based on a birth registry in Shanghai. Birth outcomes were collected from the registry. Spot urine and household salt samples were collected for iodine testing. Single-factor analysis and logistic regression were used to evaluate the association between maternal iodine status and pregnancy outcomes.

RESULTS

The median urine iodine level in pregnant women was 137.5 μg/L (interquartile range 82.4-211.5), suggesting mild deficiency according to WHO standards. The incidence of pregnancy termination, preterm birth, congenital malformations, low birth weight, and cesarean section was 3.2%, 4.3%, 1.4%, 2.7%, and 45.2% in the mildly iodine-deficient group and 3.4%, 4.5%, 1.4%, 2.7%, and 44.5% in the normal group, respectively. After adjusting for maternal age and education, trimesters, and preterm birth rate in the general population, the odds ratios for any outcome did not differ significantly between the two groups.

CONCLUSION

The present study suggests that mild maternal iodine deficiency is not associated with adverse pregnancy outcomes.

Effect of vitamin A on the relationship between maternal thyroid hormones in early pregnancy and fetal growth: A prospective cohort study

Background

Fetal growth patterns are influenced by maternal thyroid function and vitamin A level during pregnancy. Vitamin A presents interactions with thyroid tissues and hormonal systems. We examined whether vitamin A status modified the associations of maternal thyroid hormones in early pregnancy and fetal growth outcomes among euthyroid pregnant women in a prospective cohort study (n = 637).

Methods

We performed multiple linear regression and multinomial logistic regression analysis to investigate the effects of thyroid hormones in early pregnancy on fetal growth according to different levels of serum vitamin A based on median value.

Results

A 1 pmol/L increase in maternal free triiodothyronine (FT3) levels was associated with an increased birth weight of 0.080 kg (p = 0.023) in women with lower maternal vitamin A levels in early pregnancy. Increased maternal free thyroxine (FT4) was associated with decreased odds for both small size for gestational age (SGA) [odds ratios (OR) = 0.66, 95% confidence interval (CI): 0.45–0.95] and large size for gestational age (LGA) (OR = 0.66, 95% CI: 0.45–0.98) in women with higher vitamin A level in early pregnancy after adjustment for maternal prepregnancy body mass index, gestational weight gain, maternal employed, parity, gestational week at sampling, and gestational diabetes mellitus.

Conclusions

In Chinese pregnant women without overt thyroid dysfunction, maternal FT4 in early pregnancy was positively associated with optimal fetal growth among women with higher serum vitamin A concentrations.

Moderate Freshwater Fish Intake, but Not n-3 Polyunsaturated Fatty Acids, Is Associated with a Reduced Risk of Small for Gestational Age in a Prospective Cohort of Chinese Pregnant Women

BACKGROUND

Although previous studies have found that maternal fish intake is associated with fetal growth, the role of freshwater fish intake remains unknown.

OBJECTIVE

Our aim was to examine the relationships of freshwater fish and n-3 polyunsaturated fatty acids (PUFAs) intake with the risk of small for gestational age (SGA) in Chinese pregnant women.

DESIGN

This was a prospective analysis of data from the Tongji Birth cohort in Wuhan, China, from 2018 to 2021.

PARTICIPANTS/SETTINGS

This study included 1,701 pregnant women who had completed a food frequency questionnaire dietary assessment during mid-pregnancy.

MAIN OUTCOME MEASURES

Intake of fish was assessed by a semi-quantitative food frequency questionnaire. Total intake of n-3 PUFAs was the sum of data collected from both dietary and supplemental sources of n-3 PUFAs. Birth information was extracted from medical records.

STATISTICAL ANALYSES

Multivariate logistic regression models were applied to estimate odds ratios and 95% CIs.

RESULTS

The median (interquartile range) intake of freshwater fish and total n-3 PUFAs was 12.1 (4.3 to 26.4) g/d and 68.2 (24.5 to 370.0) mg/d, respectively. Moderate intake of freshwater fish was associated with reduced risk of SGA. Compared with the lowest quintile (0-3.2 g/d), the multivariable-adjusted odds ratio for women in the fourth quintile of freshwater fish intake (17.9 to 30.0 g/d) was 0.50 (95% CI 0.25 to 0.96). We found a nonlinear association between freshwater fish intake and SGA risk (P_nonlinearity = .027). However, maternal n-3 PUFAs intake was not significantly associated with SGA risk, either from total intake or from dietary sources alone.

CONCLUSIONS

Moderate freshwater fish intake during pregnancy is associated with lower risk of SGA in a Chinese population. This finding provides supportive evidence for freshwater fish intake during pregnancy, particularly for the inland areas of developing countries.

Implications of iodine deficiency by gestational trimester: a systematic review

As pregnant women are susceptible to changes in iodine, which can cause miscarriage, goiter, thyroid nodules, hypothyroidism, in addition to fetal neurological impairment or development. The aim of this study was to verify the implications of the iodine alteration in each gestational trimester and its consequences of physiological justification. The review was based on PRISMA. Searching for articles that took place in March 2020 without delimiting data. As bases consulted were the Clinical Trials, Cochrane Library, Lilacs and Medline (PubMed). The descriptors were combined as follows: "pregnancy" AND "iodine deficiency". Articles that addressed iodine deficiency and its implications were included. The selection followed the steps of reading the titles, abstracts and full articles. To assess the methodological quality of the studies, the STROBE Instruction instrument was used. The research resulted in 1,266 studies and 11 were included. In assessing methodological quality, the lowest score was and the maximum 20. According to studies, the fourth most affected by iodine loss are the second and third, it is possible to increase the volume and pneumatic nodules, subclinical hypothyroidism, pre-eclampsia, among others. The damages caused by iodine deficiency in the first or second trimester are still reversible, therefore, they need to be diagnosed early, to guarantee an iodic homeostasis and prevent damage to the health of the mother-child binomial.

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.

Thyroid Diseases During Pregnancy: Bibliometric Analysis of Scientific Publications

BACKGROUND

Bibliometric analysis can analyze development trends and predict research hotspots. We used these analyses to better understand pregnancy-related implications of thyroid diseases.

METHODS

Publications on thyroid diseases during pregnancy from 1926 to hitherto were retrieved based on the Web of Science database. The publications and references, the institutions and countries, the journals, the keywords and citations, were analyzed by utilizing VOSviewer, CiteSpace and CitNetExplorer.

RESULTS

A total of 3310 publications were retrieved and were cited 87913 times. The United States took the dominant position in outputs and collaborations. Harvard University had the most articles 86, which also had the highest h-index 30. Thyroid ranked first with 201 publications and Journal of Clinical Endocrinology Metabolism had the highest h-index 67. Among the 49 burst keywords, "antibody" had the longest burst period from 1991 to 2012, "thyroxine" had the strongest burst strength 16.7026, "hypothyroxinemia" appeared most recently in 2018. The most frequent keyword was "pregnancy" occurred 1324 times. All the top 98 frequent keywords were clustered into 4 clusters. The citation network visualization was grouped into 8 groups.

CONCLUSION

The research focus of thyroid diseases in pregnancy ranged from clinical thyroid dysfunction to milder thyroid dysfunction. Guidelines published by the American Thyroid Association enacted a crucial purpose in the treatment and development of thyroid diseases during pregnancy. Some randomized controlled studies of unresolved problems and long-term follow-up of offspring may be the direction of future research. In the meantime, bibliometric methods can help scholars choose journals, track research hotspots, and identify the direction or focus of future research.

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.

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.

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.

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.

Breast Milk Iodine Concentration Is Associated with Infant Growth, Independent of Maternal Weight

In breastfed infants, human milk provides the primary source of iodine to meet demands during this vulnerable period of growth and development. Iodine is a key micronutrient that plays an essential role in hormone synthesis. Despite the importance of iodine, there is limited understanding of the maternal factors that influence milk iodine content and how milk iodine intake during infancy is related to postnatal growth. We examined breast milk samples from near 2 weeks and 2 months post-partum in a mother-infant dyad cohort of mothers with pre-pregnancy weight status defined by body mass index (BMI). Normal (NW, BMI < 25.0 kg/m2) is compared to overweight/obesity (OW/OB, BMI ≥ 25.0 kg/m2). The milk iodine concentration was determined by inductively coupled plasma mass spectrometry. We evaluated the associations between iodine content at 2 weeks and infant anthropometrics over the first year of life using multivariable linear mixed modeling. Iodine concentrations generally decreased from 2 weeks to 2 months. We observed no significant difference in iodine based on maternal weight. A higher iodine concentration at 2 weeks was associated with a larger increase in infant weight-for-age and weight-for-length Z-score change per month from 2 weeks to 1 year. This pilot study shows that early iodine intake may influence infant growth trajectory independent of maternal pre-pregnancy weight status.

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.

Consequences of Severe Iodine Deficiency in Pregnancy: Evidence in Humans

Iodine is a necessary micronutrient for the production of thyroid hormones and normal human development. Despite the significant worldwide strategies for the prevention and control of iodine deficiency, it is still a prevalent public health issue, especially in pregnant women. Severe iodine deficiency during pregnancy and neonatal period is associated with many major and irreversible adverse effects, including an increased risk of pregnancy loss and infant mortality, neonatal hypothyroidism, cretinism, and neuropsychomotor retardation. We will review the impact of severe iodine deficiency on maternofetal, neonatal, and offspring outcomes. We will also discuss its epidemiology, classification of iodine deficiency severity, and current recommendations to prevent iodine deficiency in childbearing age and pregnant women.

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.

Iron and Iodine Status in Pregnant Women from A Developing Country and Its Relation to Pregnancy Outcomes

Birth related complications and comorbidities are highly associated with a poor nutritional status of pregnant women, whereas iron and iodine are among especially important trace elements for healthy maternal and fetal outcomes. The study compares the status of iron, iodine, and related functional parameters in pregnant and non-pregnant women from a developing country and associates the data with pregnancy complications. The concentrations of ferritin, hemoglobin (Hb), total triiodothyronine (TT3), total thyroxine (TT4), and thyroid-stimulating hormone (TSH) were determined in the blood serum of 80 pregnant women at the time of delivery and compared with 40 non-pregnant healthy controls. Spot urine samples were taken to evaluate the urinary iodine concentration (UIC). In pregnant women, ferritin, Hb concentrations, and UIC were significantly lower, and TT4 values were significantly higher compared to controls. Higher Hb levels were tendentially associated with a reduced risk for pregnancy complications (OR = 0.747, CI (95%) 0.556–1.004; p = 0.053). Regarding covariates, only previous miscarriages were marginally associated with pregnancy complications. High consumption of dairy products was associated with lower Hb and ferritin values. Our results suggest that pregnant women from a developing country have lower iron status with Hb levels being possibly associated with pregnancy complications.

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.

Maternal Iodine Status and Associations with Birth Outcomes in Three Major Cities in the United Kingdom

Severe iodine deficiency in mothers is known to impair foetal development. Pregnant women in the UK may be iodine insufficient, but recent assessments of iodine status are limited. This study assessed maternal urinary iodine concentrations (UIC) and birth outcomes in three UK cities. Spot urines were collected from 541 women in London, Manchester and Leeds from 2004–2008 as part of the Screening for Pregnancy End points (SCOPE) study. UIC at 15 and 20 weeks’ gestation was estimated using inductively coupled plasma-mass spectrometry (ICP-MS). Associations were estimated between iodine status (UIC and iodine-to-creatinine ratio) and birth weight, birth weight centile (primary outcome), small for gestational age (SGA) and spontaneous preterm birth. Median UIC was highest in Manchester (139 μg/L, 95% confidence intervals (CI): 126, 158) and London (130 μg/L, 95% CI: 114, 177) and lowest in Leeds (116 μg/L, 95% CI: 99, 135), but the proportion with UIC <50 µg/L was <20% in all three cities. No evidence of an association was observed between UIC and birth weight centile (−0.2% per 50 μg/L increase in UIC, 95% CI: −1.3, 0.8), nor with odds of spontaneous preterm birth (odds ratio = 1.00, 95% CI: 0.84, 1.20). Given the finding of iodine concentrations being insufficient according to World Health Organization (WHO) guidelines amongst pregnant women across all three cities, further studies may be needed to explore implications for maternal thyroid function and longer-term child health outcomes.

Distribution of fipronil in humans, and adverse health outcomes of in utero fipronil sulfone exposure in newborns

Fipronil is a highly effective insecticide with extensive usages; however, its distribution and toxic/health effects in the human population after chronic exposure have not yet been clearly identified. Our objectives were to determine the levels of serum fipronil and fipronil sulfone, a primary fipronil metabolite, in a general and sensitive human population using a birth cohort of parent-infant triads in Korea. We further investigated whether in utero exposure to fipronil and fipronil sulfone can affect health outcomes in newborn infants. Blood and umbilical cord blood from 169 participants, 59 mother-neonate pairs and 51 matching biological fathers, were collected; serum fipronil and fipronil sulfone (both blood and cord blood) and serum thyroid hormones (cord blood) were measured. Demographic, physiological, behavioral, clinical, and socioeconomic data for each participant were collected via a one-on-one interview and a questionnaire survey. Fipronil sulfone was detected in the serum of mothers, fathers, and infantile cord blood, while fipronil itself was not. Maternal fipronil sulfone levels were correlated to those of matched biological fathers and newborn infants. Adjusted analyses identified significant associations between parental fipronil sulfone levels and household income. Infantile fipronil sulfone levels were significantly associated with both maternal and paternal levels as well as maternal pre-pregnant BMI. Furthermore, infantile fipronil sulfone levels were inversely associated with cord blood T3 and free T3 levels as well as 5-min Apgar scores of newborn infants. Serum fipronil sulfone was detected in a specific population of mother-neonate pairs and their matched biological fathers in a manner suggestive of regular exposure to fipronil among urban residents. The findings also suggest that serum fipronil sulfone placentally transfers to the fetus and affects infantile adverse health outcomes. This is a first of its kind study; therefore, future studies are warranted.

Lactating Mothers and Infants Residing in an Area with an Effective Salt Iodization Program Have No Need for Iodine Supplements: Results from a Double-Blind, Placebo-Controlled, Randomized Controlled Trial

BACKGROUND

The necessity of iodine supplementation in lactating mothers residing in countries with sustained salt iodization programs for iodine sufficiency of breast-fed infants remains unclear. The aims of this study were to investigate the effect of iodine supplementation on iodine status and growth parameters of lactating mothers and breast-fed infants and to compare these data with that of formula-feeding mothers and their infants during the first year of infancy.

METHODS

In this multicenter, double-blinded, randomized clinical trial conducted in four healthcare centers in Tehran (Iran), healthy lactating mothers and their term newborns aged 3-5 days were randomly assigned to treatment groups: placebo, 150 μg/day iodine, or 300 μg/day iodine. They were followed up for 12 months. Formula-fed infants aged 30-45 days and their mothers were randomly selected from the same centers. The primary outcomes were maternal and infant urinary iodine concentrations (UICs), breast-milk iodine concentrations (BMICs), and infant growth parameters, measured at 1, 2, 4, 6, 9, and 12 months during routine health visits. The formula-fed group was assessed at 2, 4, 6, 9, and 12 months of age. Analysis was by per protocol principle using mixed-effects models.

RESULTS

Mother-newborn pairs (n = 180) in treatment groups and partially/exclusively formula-feeding mother-infant pairs (n = 60) participated between October 2014 and January 2016. Median baseline UICs in the treatment groups were 84 μg/L (interquartile range [IQR] 41-143 μg/L) in mothers and 208 μg/L (IQR 91-310 μg/L) in their infants. The values in the formula-fed group were 76 μg/L (IQR 40-144 μg/L) in mothers and 121 μg/L (IQR 66-243 μg/L) in infants. The 300 μg/day iodine group showed significantly higher UICs and BMICs than did the other treatment groups; infant UICs in the 150 μg/day iodine, placebo, and formula-fed groups were similar. Infants in all groups showed iodine sufficiency (median UIC ≥100 μg/L) throughout the study period. Anthropometric measurements were similar between the treatment and formula-fed groups over the study period, except at the last follow-up visit at 12 months.

CONCLUSION

Supplementation of breast-feeding mothers with either 300 or 150 μg/day iodine improved their iodine status. However, the iodine status of infants in all groups studied indicated iodine sufficiency during the first year of infancy, demonstrating that in countries with effective salt iodization program, iodine supplementation for lactating mothers is unnecessary.

Maternal Iodine Insufficiency and Excess Are Associated with Adverse Effects on Fetal Growth: A Prospective Cohort Study in Wuhan, China

Background

Maternal iodine status has been suggested to affect birth outcomes. Few studies have focused on its effects on fetal growth during pregnancy.

Objective

This study aimed to assess maternal iodine status during early pregnancy and further examine the relation between maternal iodine status and fetal growth.

Methods

A total of 2087 singleton-pregnant women participating in the Tongji Maternal and Child Health Cohort study were involved. Urinary iodine concentration (UIC) and creatinine concentration were measured in spot urine samples collected in early pregnancy (<20 wk of gestation). Fetal head circumference (HC), femur length (FL), and estimated fetal weight (EFW) were evaluated by ultrasonography in each trimester. A multiple linear regression model was used to examine the association of iodine status with fetal growth characteristics, and a mixed-effects model was used to assess longitudinal effect.

Results

The median UIC and iodine-to-creatinine (I/Cr) ratio were 178 μg/L and 234 μg/g, respectively. The prevalence of insufficient iodine status (I/Cr ratio <150 μg/g) was 19.8%(n = 414), of adequate iodine status (150-249 μg/g) was 34.8% (n = 726), of iodine status above the requirements (250-499 μg/g) was 32.1% (n = 669), and of excessive iodine status (≥500 μg/g) was 13.3% (n = 278). Maternal iodine insufficiency was inversely associated with fetal FL in the second and third trimesters. In stratified analysis, significant interactions were found between maternal iodine status and age as well as parity (all P < 0.05). The longitudinal analyses showed negative associations of maternal insufficient, more than adequate, or excessive iodine status with fetal growth during pregnancy (all P < 0.05).

Conclusions

In central China, maternal iodine insufficiency and excess coexisted during early pregnancy and they both adversely affected fetal growth. There is an urgent need for ongoing monitoring of iodine status among vulnerable pregnant women in order to optimize iodine nutrition during pregnancy.

Is there an association between thyrotropin levels within the normal range and birth growth parameters in full-term newborns?

Background It has been suggested that thyroid hormone concentration at birth may have some role in regulating foetal growth. The aim of this study was to provide seminal data regarding any association between thyrotropin (TSH) concentration within the normal range and growth parameters at birth in full-term newborns. Methods In this cross-sectional study conducted in Tehran, Iran, 314 mother-newborn pairs were randomly selected from health care centres responsible for congenital hypothyroidism screening. Neonatal TSH concentration was measured using a heel-prick blood sample taken from all neonates 3-5 days after birth, as part of the routine neonate screening. Anthropometrics, including birth weight, length and head circumference were obtained from the birth record of each neonate. The z-score values for weight-for-age, weight-for-length, length-for-age and head-for-age were calculated using the World Health Organisation growth standards. Results The median interquartile range neonatal TSH values were 0.9 mIU/L (0.4-1.7 mIU/L). Neonates in the top tertile of TSH values had higher birth weights and weight-for-age z-scores than those in the bottom tertile (p<0.05). In addition, neonatal TSH was associated with weight-for-age z-scores in unadjusted (β=0.113, p=0.020) and adjusted (β=0.122, p=0.013) analysis. However, in both unadjusted and adjusted analysis, no association was observed between TSH concentrations of neonates and weight-for-length, length-for-age and head-for-age z-scores. Conclusions Our findings indicate a positive association between the normal range of neonatal screening TSH concentration and birth weight; however, this association was not observed for other anthropometric parameters at birth.

The assessment of iodine status - populations, individuals and limitations

Iodine deficiency is a significant global health concern, and the single greatest cause of preventable cognitive impairment. It is also a growing public health concern in the UK particularly among pregnant women. Biomarkers such as urinary iodine concentration have clear utility in epidemiological studies to investigate population-level iodine status, but determination of iodine status in individuals is much more problematic with current assays. This article reviews the available biomarkers of iodine status and their relative utility at the level of both populations and individuals for the investigation of iodine deficiency and iodine excess.

Effects of Iodized Salt and Iodine Supplements on Prenatal and Postnatal Growth: A Systematic Review

Hypothyroidism due to iodine deficiency can impair physical development, most visibly in the marked stunting of myxedematous cretinism caused by severe in utero iodine deficiency. Whether iodine repletion improves growth in noncretinous children is uncertain. Therefore, the aim of our systematic review was to assess the effects of iodine fortification or supplementation on prenatal and postnatal growth outcomes in noncretinous children. Following Cochrane methods and PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) reporting guidelines, we searched 10 databases including 2 Chinese databases (latest search February 2017). We included randomized and nonrandomized controlled trials (RCTs; non-RCTs), controlled before-after (CBA) studies, and interrupted time-series studies in pregnant women and children (≤18 y), which compared the effects of iodine (any form, dose, regimen) to placebo, noniodized salt, or no intervention on prenatal and postnatal growth outcomes. We calculated mean differences with 95% CIs, performed random-effects meta-analyses, and assessed the quality of evidence with the use of GRADE (Grading of Recommendations Assessment, Development and Evaluation). We included 18 studies (13 RCTs, 4 non-RCTs, 1 CBA) (n = 5729). Iodine supplementation of severely iodine-deficient pregnant women increased mean birthweight [mean difference (MD): 200 g; 95% CI: 183, 217 g; n = 635; 2 non-RCTs] compared to controls, but the quality of this evidence was assessed as very low. Iodine repletion across the other groups showed no effects on primary growth outcomes (quality of evidence mostly low and very low). Meta-analyses showed a positive effect in moderate-to-mildly iodine-deficient schoolchildren on insulin-like growth factor-1 (MD: 38.48 ng/mL; 95% CI: 6.19, 70.76 ng/mL; n = 498; 2 RCTs, low-quality evidence) and insulin-like growth factor binding protein-3 (MD: 0.46 μg/mL; 95% CI: 0.25, 0.66 μg/mL; n = 498; 2 RCTs, low-quality evidence). In conclusion, we identified few well-designed trials examining the effects of iodine repletion on growth. We are uncertain whether prenatal iodine repletion increases infant growth. Postnatal iodine repletion may improve growth factors but has no clear effects on somatic growth. Our systematic review was registered with PROSPERO as CRD42014012940.

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

CONTEXT

Overt thyroid disease in pregnancy is a known risk factor for abnormal fetal growth and development. Data on the effects of milder forms of variation in maternal thyroid function on intrauterine growth are less well examined.

OBJECTIVE

We explored these associations using repeated thyroid hormone and ultrasound measurements.

DESIGN, SETTING, AND PARTICIPANTS

Data were obtained from 439 pregnant women without diagnosed thyroid disease who were participants in a case-control study of preterm birth nested within an ongoing prospective birth cohort in Boston, Massachusetts.

MAIN OUTCOME MEASURES

Ultrasound and delivery indices of fetal growth were standardized to those measured in a larger population.

RESULTS

At median 10, 18, and 26 weeks of gestation, we observed significant inverse associations between free thyroxine (FT4) and birth weight z scores, with the strongest association detected at median 10 weeks, at which time a 10% increase in FT4 was associated with a 0.02 z score decrease (∼8.5 g) in birth weight (β = -0.41 for ln-transformed FT4; 95% confidence interval, -0.64 to -0.18). FT4 was also inversely associated with repeated measurements of estimated fetal weight, head circumference, and abdominal circumference. We observed weaker inverse associations for total T4 and a positive relationship between total triiodothyronine and birth weight z scores. We did not observe any associations for thyroid-stimulating hormone.

CONCLUSION

In pregnant women without overt thyroid disease, subclinical changes in thyroid function parameters may influence fetal growth.

Iodine Status during Pregnancy in a Region of Mild-to-Moderate Iodine Deficiency is not Associated with Adverse Obstetric Outcomes; Results from the Avon Longitudinal Study of Parents and Children (ALSPAC)

Severe iodine deficiency during pregnancy has been associated with pregnancy/neonatal loss, and adverse pregnancy outcomes; however, the impact of mild–to–moderate iodine insufficiency, though prevalent in pregnancy, is not well-documented. We assessed whether mild iodine deficiency during pregnancy was associated with pregnancy/infant loss, or with other adverse pregnancy outcomes. We used samples and data from the Avon Longitudinal Study of Parents and Children (ALSPAC), from 3140 singleton pregnancies and from a further 42 women with pregnancy/infant loss. The group was classified as mildly-to-moderately iodine deficient with a median urinary iodine concentration of 95.3 µg/L (IQR 57.0–153.0; median urinary iodine-to-creatinine ratio (UI/Creat) 124 µg/g, IQR 82–198). The likelihood of pregnancy/infant loss was not different across four UI/Creat groups (<50, 50–149, 150–250, >250 µg/g). The incidence of pre-eclampsia, non-proteinuric gestational hypertension, gestational diabetes, glycosuria, anaemia, post-partum haemorrhage, preterm delivery, mode of delivery, being small for gestational age, and large for gestational age did not differ significantly among UI/Creat groups, nor were there any significant differences in the median UI/Creat. We conclude that maternal iodine status was not associated with adverse pregnancy outcomes in a mildly-to-moderately iodine-deficient pregnant population. However, in view of the low number of women with pregnancy/infant loss in our study, further research is required.

Association of in utero exposure to organochlorine pesticides with thyroid hormone levels in cord blood of newborns

Organochlorine pesticides (OCPs) had been widely used in agriculture and disease prevention from the 1940s-1960s. Currently, OCPs are raising global concerns due to their associated prevalent contamination and adverse health effects, such as endocrine disruption. Several epidemiological studies have explored the underlying association of OCPs on thyroid hormone (TH) status in adults and newborns, but the results of studies performed on newborns are often inconclusive. This exploratory study was conducted with the purpose of assessing the potential association of the prenatal exposure to OCPs with the concentrations of TH in the cord blood of newborns from China. Cord blood and information on demographic characteristics were collected from 115 newborns between November 2013 and June 2014. The exposure levels of 17 OCPs were measured with a gas chromatography/mass spectrometry, and TH levels including free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were detected using electrochemiluminescence immunoassay methods. After adjusting for confounding factors (the age of pregnant mothers, education level, monthly household income, parity, and sex of the newborns), we found marginally significant inverse associations of cord plasma measurements of ∑hexachlorcyclohexanes (∑HCHs), 1,1-dichloro-2,2-di(4-chlorophenyl)ethylene (ρ,ρ'-DDE) and methoxychlor with FT4 levels, but not with FT3 and TSH levels. Moreover, higher cord plasma levels of aldrin, dieldrin, ∑dichlorodiphenyltrichloroethanes (∑DDTs), ∑Drins, and ∑OCPs were found to be related to the increase in cord plasma TSH levels after the adjustment for confounders. The results of this exploratory study indicate that in utero exposure to certain OCPs may affect TH status in newborns, and therefore, pose potential effects on early human development. Further research, with larger sample sizes, should be conducted to confirm these findings.

Maternal iodine status during lactation and infant weight and length in Henan Province, China

BACKGROUND

Infants are very sensitive to iodine deficiency. Breastfed infants are dependent on maternal iodine intake. The aim of this study was to evaluate the relationship between maternal iodine status during lactation and infant weight and length.

METHODS

A cross-sectional survey was conducted to investigate maternal iodine status and infant anthropometric measures in Henan Province, China. Only exclusive breastfeeding mothers and their infants < 6 months of age (n = 747) were included in our final analysis. Urine samples were collected from all the mothers and infants. Infant weight and length were measured and converted into weight-for-age Z-score (WAZ) and height-for-age Z-score (HAZ) using the World Health Organization (WHO) AnthroPlus software.

RESULTS

The median urinary iodine concentration (UIC) in lactating women was significant lower than that in their infants (177.4 vs 261.1 μg/L, P < 0.001). A positive correlation was found between maternal and infant urinary iodine concentration (r = 0.203, P < 0.01). The mean HAZ and WAZ values were lowest in the infants whose mothers had UIC below 50 μg/L (n = 41). Infant WAZ with maternal UIC below 50 μg/L was significantly lower than those with maternal UIC of 50 μg/L or above (P = 0.043). After adjusting for confounding factors, there were significant differences in infant WAZ between maternal UIC groups.

CONCLUSIONS

The present study suggests that maternal iodine status during lactation may be related to their infant anthropometric index. Appropriate iodine intake of lactating women is beneficial for their infants.

EVALUATION OF URINARY IODINE LEVELS AND THYROID FUNCTION TESTS IN PREGNANT WOMEN AND THEIR INFANTS

Introduction

In this study we aimed to evaluate urinary iodine excretion and the serum levels of thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4) and thyroglobulin (Tg) in pregnants and their newborn infants.

Materials and Methods

This study was performed in Konya Faruk Sukan Children and Maternity Hospital, Konya Beyhekim State Hospital and Hospital of Selcuk University Medical Faculty. 180 pregnant women and their healthy infants born at 37-40 gestational weeks.Term infants included in this study were aged between 1-7 days, healthy. Midurination urine samples were taken into deiodinized plastic bottles and 2 mL of these samples were aliquoted to deiodinized eppendorf tubes.

Results

Median urinary iodine concentration (UIC) was 95.5 µg/L for pregnant women and 245 µg/L for their infants. Frequency of iodine deficiency was observed as 63.3% (n=114) (<150 µg/L) and 24.4% (n=44) (<100 µg/L) in mothers and their infants, respectively. UIC of the infants whose mothers used iodized salt was significantly higher than the one whose mothers used rocksalt (p=0.030).

Conclusions

It was stated in our study that UIC of pregnants was lower than the target limit (<150 µg/L), suggested by World Health Organisation (WHO) and iodine deficiency in pregnants is still a problem in our city located in the centre of Turkey. Iodine deficiency was observed in 24.4% of the infants and this prevalence suggests us that iodine deficiency is still an important health problem in infants.

Iodine Status of Vulnerable Populations in Henan Province of China 2013-2014 After the Implementation of the New Iodized Salt Standard

The standard of salt iodine content in China has been adjusted several times since implementation of the universal salt iodization (USI) in 1995. The new standard of iodized salt content was adjusted from 35 ± 15 to 30 ± 9 mg/kg in Henan province in 2012. We aimed to determine whether the vulnerable populations were iodine sufficient after the adjustment of salt iodine content and to provide a guideline for the adjustment of USI policy in China. Two cross-sectional surveys of iodine status in vulnerable populations, including reproductive-age, pregnant and lactating women, infants <2 years, and children aged 8-10 years, were conducted in Henan province in 2013 and 2014. In 2013, the median urinary iodine concentration (mUIC) of reproductive-age women was 200.1 μg/L and that of school children aged 8-10 years was 221.0 μg/L. These mUICs were considered as "more than adequate." The mUICs of reproductive-age women and school children in 2014 showed a significant decline compared to the mUICs in 2013 (P = 0.012 and P = 0.001, respectively). The mUICs of the pregnant women were 204.2 μg/L in 2013 and 202.5 μg/L in 2014, which both met the requirement level recommended by WHO. In 2013, the mUIC of lactating women was 169.1 μg/L and that of infants <2 years was 203.2 μg/L, which were significantly lower than that of 2014 (P < 0.001 and P < 0.001, respectively). The lactating women and infants in 2013 and 2014 were both regarded as "iodine adequate." Iodine status of the vulnerable populations is still adequate as a whole in Henan province after decreasing the salt iodine content. However, the mUIC of school children aged 8-10 years is slightly above the adequate level. To reduce the risk of iodine excess in the general population and prevent the possibility of iodine deficiency of the vulnerable population, it is necessary to explore the appropriate level of iodized salt content.

Inadequate iodine nutrition of pregnant women in an area of iodine sufficiency

PURPOSE

I. R. Iran has been considered iodine replete since 2000, but iodine nutrition of vulnerable subjects is not clear. The main goal of this study was assessment of iodine nutrition and thyroid function in pregnant Iranian women.

METHODS

A total of 1072 pregnant women from ten provinces in the different parts of the country were recruited from November to March 2014. Median urinary iodine concentration (UIC) as the measure of iodine status and serum free T4 (FT4), thyrotropin (TSH), thyroglobulin (Tg), anti-thyroglobulin and anti-thyroid peroxidase antibodies (TgAb and TPOAb) were measured.

RESULTS

Mean ± SD age of the cohort was 27.0 ± 7.2 years and gestational age was 20.7 ± 10.0 weeks. The median UIC for pregnant women was 87.3 μg/L, being 92.1, 86.0 and 76.8 μg/L, in three trimesters of pregnancy, respectively. Median UIC of <100, 100-149, 150-249, 250-499 and ≥500 μg/L was found in 58.4, 19.8, 16.2, 5.13 and 0.46 % of subjects, respectively. Median (IQR) values in the first, second, and third trimesters were 1.7 (0.9-2.8), 2.1 (1.5-2.9), and 2.1 (1.4-2.8) mIU/L for TSH, and 16.4 (12.21-21.13), 14.34 (12.16-19.69), and 14/07 (12.02-18.64) pmol/L for FT4, respectively. The frequency of elevated serum TSH was 9.0 % (6.6 % subclinical, 2.4 % overt hypothyroidism). The frequency of low serum TSH was 0.6 %. The frequency of positive TPOAb was 7.6 %.

CONCLUSIONS

Results of this study have clarified that despite iodine sufficiency of school children in Iran, pregnant women have moderate iodine deficiency and need iodine supplementation.

The Urine Iodine to Creatinine as an Optimal Index of Iodine During Pregnancy in an Iodine Adequate Area in China

CONTEXT

Iodine nutrition is a global event, especially for pregnant women.

OBJECTIVE

To develop applicable index of iodine intake for population during pregnancy.

DESIGN, SETTING, AND PARTICIPANTS

From 2012 to 2014, pregnant women at less than 8 weeks of gestation (n = 222) and reproductive-age women (n = 827) participated in this study. The pregnant women were evaluated at follow-up visits at 8, 12, 16, 20, 28, and 36 weeks of gestation and 3 and 6 months postpartum.

MAIN OUTCOME MEASURES

Twenty-four-hour urine samples were collected at weeks 8 of gestation. Urine iodine (UI) and creatinine (Cr) and serum thyroglobulin were measured in all of the subjects. Circulatory iodine was measured using inductively coupled plasma-mass spectrometry at 8, 20, and 36 weeks of gestation and 6 months postpartum.

RESULTS

The median UI concentration decreased from 183.6 to 104.2 μg/L during pregnancy. The serum iodine (SI) changes were similar to the UI to creatinine ratio (UI/Cr). The SI level was lowest at the eighth week of gestation (60.5 μg/L), which rose significantly until 20 weeks (106.5 μg/L) and then began to decline (36 wk, 84.7 μg/L). The 24-hour UI excretion measurement was regarded as the gold standard. The area under the receiver-operating characteristic curve for UI/Cr was 0.92 for iodine deficiency diagnoses and 0.78 for SI. The area for SI was 0.82 for excessive iodine diagnoses and 0.75 for UI/Cr. The areas under these curves were significantly different (P < .001). The areas under the receiver-operating characteristic curve for UI were 0.61 (P = .11) and 0.65 (P = .08) for iodine deficiency and excessive iodine diagnoses, respectively. Additionally, for thyroglobulin, these values were 0.54 (P = .53) and 0.53 (P = .74), respectively.

CONCLUSIONS

Iodine intake, as assessed by spot UI concentration in pregnant women, is inaccurate and increases the prevalence of iodine deficiency. The UI/Cr better reflects the 24-hour iodine excretion and circulating iodine levels during pregnancy and the postpartum period.

Iodine status of pregnant women in a metropolitan city which proved to be an iodine-sufficient area. Is mandatory salt iodisation enough for pregnant women?

The objective of this study was to assess the iodine status of pregnant women in a metropolitan city which was stated as iodine sufficient area after salt iodination program. This multicenter, cross-sectional study was carried out on 3543 pregnant women. Age, gestational weeks, smoking, consumption of iodized salt, dietary salt restriction, history of stillbirth, abortus and congenital malformations were questioned. Spot urine samples were analyzed for urine iodine concentration (UIC). The outcomes were: (a) median UIC in three trimesters of pregnancy and (b) frequency of ID among pregnant women. The median UIC was 73 µg/L. The median UIC was 77 µg/L (1-324), 73 µg/L (1-600) and 70 µg/L (1-1650) in three trimesters of pregnancy, respectively (p: 0.14). UIC <50 µg/L was observed in 36.6% (n: 1295) and UIC<150 µg/L was observed in 90.7% (n: 3214) of pregnant women. Only 1% (n: 34) of the pregnant women had UIC levels higher than 500 µg/L. This study showed that more than 90% of the pregnant women in this iodine-sufficient city are facing some degree of iodine deficiency during their pregnancy. A salt iodization program might be satisfactory for the non-pregnant population, but it seems to be insufficient for the pregnant population.

Maternal iodine status and the thyroid function of pregnant mothers and their neonates in Jaffna District of Sri Lanka

INTRODUCTION

Iodine status of pregnant women and their newborns have not been studied in Jaffna District, Sri Lanka. This study was planned to assess the maternal iodine status and thyroid function at the third trimester of gestation and the thyrotrophin level of their neonate.

METHODS

Four hundred and seventy-seven pregnant women and their newborns were randomly selected among six Medical Officers of Health Divisions out of 12 in Jaffna District, Sri Lanka. Maternal thyroid stimulating hormone (TSH), free thyroxine (fT4), thyroglobulin (Tg), urinary iodine levels, and the neonatal thyrotrophin (nTSH) level were assessed.

RESULTS

In this study, mean age, weight, height, and gestational age of the mothers were 28.95 (±5.46) years, 63.02 (±11.56) kg, 154.39 (±6.00) cm, and 39.33 (±1.37) weeks, respectively. Maternal median urinary iodine concentration (UIC) was 140.0 μg/L (inter-quartile range 126.0-268.0 μg/L). Median values of the maternal serum TSH, fT4, and Tg were 1.9 mIU/L, 12.6 pmol/L, and 21.4 IU/L, respectively. Among the 477 newborns, 50.5% (n = 239) were males. Mean birth weight of newborn was 3.03 (±0.43) kg, while the mean length was 51.1 (±2.1) cm. Among the newborns, 18% (n = 86) had nTSH level > mIU/L and 37.7% (n = 180) within TSH level > mIU/L. nTSH level had positive but very weak correlations with maternal thyroid parameters, that is, UIC (r = 0.06, P = 0.13), fT4 (r = 0.01, P = 0.05), TSH (r = 0.09, P = 0.05), and Tg (r = 0.12, P = 0.03).

CONCLUSION

On the basis of the World Health Organization criteria, the iodine status of pregnant women was inadequate in this region and also nTSH levels indicate moderate iodine deficiency during pregnancy. Therefore, the continuous education on adequate iodine intake during pregnancy and monitoring of iodine status are useful.

Maternal iodine insufficiency and adverse pregnancy outcomes

This study aimed to assess the iodine status of pregnant women in each trimester and to compare the pregnancy outcomes between groups with iodine insufficiency and iodine sufficiency. Longitudinal study on urinary iodine concentration (UIC) in each trimester as well as comparison between women with iodine insufficiency (<150 mcg L(-1) ) and iodine sufficiency was conducted. Pregnant women without thyroid diseases who had not received iodine supplementation were recruited for UIC measurements in each trimester and were followed up for pregnancy outcomes. In the analysis of 384, 325 and 221 samples in the first, second and third trimester, the medians of UICs were 147.39, 157.01 and 153.07 mcg L(-1) , respectively. Of 399 women, 174 (43.6%) had a UIC less than 150 mcg L(-1) (suggesting iodine insufficiency) and 225 (56.4%) had a UIC greater than or equal to 150 mcg L(-1) (suggesting iodine sufficiency). Of 390 women with availability of the final outcomes, 171 and 219 in the insufficiency and sufficiency group, respectively, the rates of preterm birth and low birthweight were significantly higher in the insufficiency group, 17.5% vs. 10.0% (P = 0.031) and 19.9% vs. 12.3% (P = 0.042), respectively. Logistic regression analysis showed that iodine status was an independent risk of preterm birth and low birthweight. Finally, women with a UIC <100 mcg L(-1) had a significantly higher rate of fetal growth restriction, 13/68 vs. 30/322 (P = 0.031). In northern Thailand, a great number of pregnant women had a median UIC less than 150 mcg L(-1) and they had a higher risk of preterm birth and low birthweight. Finally, those with a median UIC of less than 100 mcg L(-1) had a higher risk of fetal growth restriction.

Gestational changes in iodine status in a cohort study of pregnant women from the United Kingdom: season as an effect modifier

BACKGROUND

Iodine is required throughout pregnancy for thyroid hormone production, which is essential for fetal brain development. Studies of iodine status in pregnant women from the United Kingdom (UK) have focused on early gestation (<16 wk). Data on the effect of advancing gestation on urinary iodine excretion are conflicting, with suggestions of both an increase and a decrease.

OBJECTIVES

The aims were to evaluate iodine status in a cohort of UK pregnant women and to explore how it changes throughout gestation.

DESIGN

We used samples and data from 230 UK pregnant women who were recruited to the Selenium in PRegnancy INTervention study. Iodine concentration was measured in spot-urine samples that were collected at ∼12, 20, and 35 wk of gestation; creatinine concentration was also measured to correct for urine dilution. A linear mixed model was used to explore the effect of gestational week on iodine-to-creatinine ratio, with change in season, body mass index, daily milk intake, and maternal age controlled for.

RESULTS

The median urinary iodine concentration from urine samples collected at all time points (n = 662) was 56.8 μg/L, and the iodine-to-creatinine ratio was 116 μg/g, thus classifying this cohort as mildly-to-moderately iodine deficient. The median iodine-to-creatinine ratios at 12, 20, and 35 wk were 102.5, 120.0, and 126.0 μg/g, respectively. Only 3% of women were taking iodine-containing prenatal supplements. The iodine-to-creatinine ratio increased with advancing gestation, and there was a significant interaction between gestational week and season (P = 0.026). For a 1-wk increase in gestation, the iodine-to-creatinine ratio increased by a factor of 1.05 (95% CI: 1.02, 1.08) in winter and by a factor of 1.04 (95% CI: 1.00, 1.08) in summer.

CONCLUSIONS

This group of UK pregnant women was mildly-to-moderately iodine deficient at all trimesters, which is of public health concern. The finding that the iodine-to-creatinine ratio increased over the course of gestation may not be generalizable to populations with different iodine status from ours and merits further investigation. This trial was registered at www.isrctn.com as ISRCTN37927591.

Systematic review of the effects of iodised salt and iodine supplements on prenatal and postnatal growth: study protocol

INTRODUCTION

Iodine is an essential micronutrient and component of the thyroid hormones. Sufficient ingestion of iodine is necessary for normal growth and development. If iodine requirements are not met, growth can be impaired. Salt iodisation and supplementation with iodine can prevent iodine deficiency disorders and stunted growth. No systematic review has yet collated the evidence linking iodine to growth. With an increased emphasis on stunting within the WHO Global Nutrition Targets for 2025, we propose a systematic review to address this question.

METHODS AND ANALYSIS

We will undertake a systematic review, and if appropriate, meta-analyses, evaluating the effects of iodised salt or iodine supplements on prenatal and postnatal somatic growth, until age 18. We will search a number of databases, including MEDLINE, EMBASE, Web of Science, CINAHL, PsychINFO, the Cochrane Library, including the CENTRAL register of Controlled Trials and also the WHO library and ICTRP (International Clinical Trials Registry Platform), which includes the Clinicaltrials.gov repository. We will also search Wanfang Data and the China Knowledge Resource Integrated Database. Included studies must have compared exposure to iodised salt, iodine supplements or iodised oil, to placebo, non-iodised salt or no intervention. Primary outcomes will be continuous and categorical markers of prenatal and postnatal somatic growth. Secondary outcomes will cover further measures of growth, including growth rates and indirect markers of growth such as insulin-like growth factor-1 (IGF-1).

ETHICS AND DISSEMINATION

The systematic review will be published in a peer-reviewed journal, and will be sent directly to the WHO, United Nations Children's Fund, International Council for the Control of Iodine Deficiency Disorders and other stakeholders. The results generated from this systematic review will provide evidence to support future programme recommendations regarding iodine fortification or supplementation and child growth.

TRIAL REGISTRATION NUMBER

PROSPERO CRD42014012940.