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

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 Thyroid Function in Early Pregnancy and Child Attention-Deficit Hyperactivity Disorder: An Individual-Participant Meta-Analysis

Background: Thyroid hormone is essential for optimal fetal brain development. Evidence suggests that both low and high maternal thyroid hormone availability may have adverse effects on child neurodevelopmental outcomes, but the effect on behavioral problems remains unclear. We studied the association of maternal thyrotropin (TSH) and free thyroxine (fT4) concentrations during the first 18 weeks of pregnancy with child attention-deficit hyperactivity disorder (ADHD). Methods: A total of 7669 mother-child pairs with data on maternal thyroid function and child ADHD were selected from three prospective population-based birth cohorts: INfancia y Medio Ambiente (INMA; N = 1073, Spain), Generation R (N = 3812, The Netherlands), and Avon Longitudinal Study of Parents and Children (ALSPAC; N = 2784, United Kingdom). Exclusion criteria were multiple pregnancy, fertility treatment, usage of medication affecting the thyroid, and pre-existing thyroid disease. We used logistic regression models to study the association of maternal thyroid function with the primary outcome, ADHD, assessed via the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) criteria by parents and/or teachers at a median child age of 4.5 to 7.6 years, and with the secondary outcome, an ADHD symptom score above the 90th percentile. Effect modification by gestational age and sex was tested with interaction terms and stratified analyses. Results: Overall, 233 (3%) children met the criteria for ADHD. When analyzed continuously, neither fT4 nor TSH was associated with a higher risk of ADHD (odds ratio [OR] 1.1, 95% confidence interval [CI 1.0-1.3], p = 0.060 and OR 0.9 [CI 0.9-1.1], p = 0.385, respectively) or with high symptom scores. When investigating effect modification by gestational age, a higher fT4 was associated with symptoms above the 90th percentile but only in the first trimester (for fT4 per 1 SD: OR 1.2 [CI 1.0-1.4], p = 0.027). However, these differential effects by gestational age were not consistent. No significant effect modification by sex was observed. Conclusions: We found no clear evidence of an association between maternal thyroid function and child ADHD.

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.

Evaluation of Maternal Exposure to PM2.5 and Its Components on Maternal and Neonatal Thyroid Function and Birth Weight: A Cohort Study

Background: Particulate matter (PM) air pollution is an environmental risk to public health. The prevalence of thyroid disease during pregnancy has increased rapidly in recent decades, but the available data on the relationships among air pollution, thyroid function, and birth outcomes in pregnant women, particularly in China, are scarce. We aimed to evaluate the association between maternal exposure to PM_2.5 and its components and maternal and neonatal thyroid function and to investigate whether thyroid function acts as a mediator between air pollution and birth weight. Methods: In this prospective birth cohort study, the levels of maternal exposure to PM_2.5 and its components during the first trimester were assessed in 433 pregnant women in Nanjing, China, enrolled during 2014-2015. We evaluated the levels of maternal exposure to PM_2.5 and its six main constituents-organic matter (OM), black carbon (BC), sulfate (SO₄^2-), nitrate (NO₃^-), ammonium (NH₄⁺), and soil dust-using the V4.CH.02 product of the Dalhousie University Atmospheric Composition Analysis Group. The maternal serum-free thyroxine (fT4), thyrotropin (TSH), and thyroid peroxidase antibody (TPOAb) levels during the second trimester were measured through electrochemiluminescent microparticle immunoassays. The neonatal TSH levels were detected using an AutoDELFIA Neonatal TSH kit within 72 hours after birth, and the birth weight Z-score of each newborn was estimated. Results: Higher exposure to maternal PM_2.5 and some components (BC and NH₄⁺) decreased the maternal fT4 level (p < 0.05), and the birth weight Z-score was decreased (p < 0.05) by higher exposure to maternal PM_2.5 and some components (OM, BC, NO₃^-, and NH₄⁺). A mediation analysis clarified that the maternal fT4 levels explained 15.9%, 18.4%, and 20.9% of the associations of maternal PM_2.5, BC, and NH₄⁺ exposure with the birth weight Z-score, respectively (p < 0.05). After additional sensitivity analyses including only nonpreterm participants (n = 418) and non-TPOAb-positive participants (n = 415), the models remained stable. Conclusions: Our results suggest an inverse association between maternal exposure to PM_2.5 and its components and the maternal fT4 levels. Maternal fT4 might act as a mediator between exposure to PM_2.5 and its components and birth weight.

Competition for nutrients in pregnant adolescents: consequences for maternal, conceptus and offspring endocrine systems

The competition for nutrients that arises when pregnancy coincides with continuing or incomplete growth in young adolescent girls increases the risk of preterm delivery and low birthweight with negative after-effects for mother and child extending beyond the perinatal period. Sheep paradigms involving nutritional management of weight and adiposity in young, biologically immature adolescents have allowed the consequences of differential maternal growth status to be explored. Although nutrient reserves at conception play a modest role, it is the dietary manipulation of the maternal growth trajectory thereafter which has the most negative impact on pregnancy outcome. Overnourishing adolescents to promote rapid maternal growth is particularly detrimental as placental growth, uteroplacental blood flows and fetal nutrient delivery are perturbed leading to a high incidence of fetal growth restriction and premature delivery of low birthweight lambs, whereas in undernourished adolescents further maternal growth is prevented, and depletion of the maternal body results in a small reduction in birthweight independent of placental size. Maternal and placental endocrine systems are differentially altered in both paradigms with downstream effects on fetal endocrine systems, organ development and body composition. Approaches to reverse these effects have been explored, predominantly targeting placental growth or function. After birth, growth-restricted offspring born to overnourished adolescents and fed to appetite have an altered metabolic phenotype which persists into adulthood, whereas offspring of undernourished adolescents are largely unaffected. This body of work using ovine paradigms has public health implications for nutritional advice offered to young adolescents before and during pregnancy, and their offspring thereafter.

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.

Differences in Diagnostic Criteria Mask the True Prevalence of Thyroid Disease in Pregnancy: A Systematic Review and Meta-Analysis

BACKGROUND

The reported prevalence of thyroid disease in pregnancy varies widely through the published literature. These discrepancies are due to differences in criteria for euthyroidism, nationality, iodine status, and gestational age at screening. As a result, currently, an accepted rate of prevalence does not exist for the various thyroid diseases in pregnancy. Understanding the true prevalence rates of these disorders has important implications for clinical management and the ongoing discussion regarding universal screening. The aims of this study were to assess (i) the true prevalence of thyroid disorders in pregnancy and (ii) the impact of diagnostic methodology on these rates.

METHODS

A systematic review was conducted of the existing literature, including the Pubmed database and references from relevant review articles. Sixty-three studies reporting prevalence of overt hypothyroidism, subclinical hypothyroidism, isolated hypothyroxinemia, subclinical hyperthyroidism, and overt hyperthyroidism in pregnant women were included. Studies were further classified by thyrotropin (TSH) cutoff for diagnosis in hypothyroid disease and timing of screening for hyperthyroid disease. Meta-analysis yielded pooled prevalence rates, with subgroup analyses for TSH cutoff and timing of screening. Analysis of studies using the 97.5th percentile TSH cutoff was assessed to yield the most accurate prevalence rates for hypothyroidism.

RESULTS

Pooled prevalence rates for hypothyroidism calculated from studies using the 97.5th percentile as an upper limit for TSH were 0.50% for overt hypothyroidism, 3.47% for subclinical hypothyroidism, and 2.05% for isolated hypothyroxinemia. Pooled prevalence rates in the first and second trimesters for hyperthyroidism were 0.91% and 0.65%, respectively, for overt hyperthyroidism and 2.18% and 0.98%, respectively, for subclinical hyperthyroidism.

CONCLUSION

Population-based, trimester-specific TSH cutoffs for diagnosis of hypothyroid disease in pregnancy result in more accurate diagnosis and better estimates for prevalence of disease. Prevalence of hyperthyroidism in pregnancy varies depending on timing of screening. The prevalence rates reported in this study represent the best estimate to date of the true rates of thyroid disease in pregnancy.

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.

Impact of levothyroxine therapy on obstetric, neonatal and childhood outcomes in women with subclinical hypothyroidism diagnosed in pregnancy: a systematic review and meta-analysis of randomised controlled trials

OBJECTIVE

To determine in women with subclinical hypothyroidism diagnosed in pregnancy whether levothyroxine treatment compared with control, impacts important obstetrical or childhood outcomes (specifically IQ) in randomised controlled trials.

DESIGN

Systematic review and meta-analysis.

STUDY ELIGIBILITY CRITERIA

Randomised trials which met all the following were included: (1) reported original data of women with subclinical hypothyroidism diagnosed in pregnancy (by any prespecified study definition); (2) randomised to either levothyroxine or control (placebo or no treatment); (3) reported obstetrical outcomes and/or childhood neurodevelopmental outcomes and (4) published from 1980 to January 2018 in either English or French language.

DATA SOURCES

Medline, EMBASE, CINAHL, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials and ClinicalTrials.gov.

OUTCOME MEASURES

Obstetrical, neonatal and childhood outcomes including: miscarriage, gestational hypertension, pre-eclampsia, preterm delivery, mode of delivery, neonatal intensive care unit admission, birth weight, gestational age at delivery, childhood IQ and neurodevelopmental scores. Risk of bias assessment Cochrane Risk of Bias Tool (Modified) for Quality Assessment of Randomised Controlled Trials RESULTS: Three trials of low to unclear risk of bias with 1837 participants were included. Two studies were meta-analysed for maternal and neonatal outcomes and two studies for childhood IQ. No statistically significant differences were found for any clinical outcomes with levothyroxine therapy compared with control.

LIMITATIONS

Only three trials were identified for inclusion.

CONCLUSIONS

This review, based on three randomised trials in women with subclinical hypothyroidism diagnosed in pregnancy, found no evidence of benefit of levothyroxine therapy on obstetrical, neonatal, childhood IQ or neurodevelopmental outcomes. Current trial evidence does not support the treatment of subclinical hypothyroidism diagnosed in pregnancy.

PROSPERO REGISTRATION NUMBER

CRD4201707980.

Thyroid Function in Early Pregnancy, Child IQ, and Autistic Traits: A Meta-Analysis of Individual Participant Data

CONTEXT

Low maternal free T4 (FT4) has been associated with poor child neurodevelopment in some single-center studies. Evidence remains scarce for the potential adverse effects of high FT4 and whether associations differ in countries with different iodine status.

OBJECTIVE

To assess the association of maternal thyroid function in early pregnancy with child neurodevelopment in countries with a different iodine status.

DESIGN, SETTING, AND PARTICIPANTS

Meta-analysis of individual participant data from 9036 mother-child pairs from three prospective population-based birth cohorts: INMA [Infancia y Medio Ambiente (Environment and Childhood project) (Spain)], Generation R (Netherlands), and ALSPAC (Avon Longitudinal Study of Parents and Children, United Kingdom). The exclusion criteria were multiple pregnancies, fertility treatments, thyroid-interfering medication usage, and known thyroid disease.

MAIN OUTCOMES

Child nonverbal IQ at 5 to 8 years of age, verbal IQ at 1.5 to 8 years of age, and autistic traits within the clinical range at 5 to 8 years of age.

RESULTS

FT4 <2.5th percentile was associated with a 3.9-point (95% CI, -5.7 to -2.2) lower nonverbal IQ and a 2.1-point (95% CI, -4.0 to -0.1) lower verbal IQ. A suggestive association of hypothyroxinemia with a greater risk of autistic traits was observed. FT4 >97.5th percentile was associated with a 1.9-fold (95% CI, 1.0 to 3.4) greater risk of autistic traits. No independent associations were found with TSH.

CONCLUSIONS

Low maternal FT4 was consistently associated with a lower IQ across the cohorts. Further studies are needed to replicate the findings of autistic traits and investigate the potential modifying role of maternal iodine status. FT4 seems a reliable marker of fetal thyroid state in early pregnancy, regardless of the type of immunoassay.

Prenatal exposure to endocrine disrupting chemicals and risk of being born small for gestational age: Pooled analysis of seven European birth cohorts

BACKGROUND AND AIMS

There is evidence that endocrine disrupting chemicals (EDCs) have developmental effects at environmental concentrations. We investigated whether some EDCs are associated with the adverse birth outcome Small for Gestational Age (SGA).

METHODS

We used PCB 153, p,p'-DDE, HCB, PFOS and PFOA measured in maternal, cord blood or breast milk samples of 5446 mother-child pairs (subset of 693 for the perfluorinated compounds) from seven European birth cohorts (1997-2012). SGA infants were those with birth weight below the 10th percentile for the norms defined by gestational age, country and infant's sex. We modelled the association between measured or estimated cord serum EDC concentrations and SGA using multiple logistic regression analyses. We explored effect modification by child's sex and maternal smoking during pregnancy.

RESULTS

Among the 5446 newborns, 570 (10.5%) were SGA. An interquartile range (IQR) increase in PCB 153 was associated with a modestly increased risk of SGA (odds ratio (OR) of 1.05 [95% CI: 1.04-1.07]) that was stronger in girls (OR of 1.09 [95% CI: 1.04-1.14]) than in boys (OR of 1.03 [95% CI: 1.03-1.04]) (p-interaction = 0.025). For HCB, we found a modestly increased odds of SGA in girls (OR of 1.04 [95% CI: 1.01-1.07] per IQR increase), and an inverse association in boys (OR of 0.90 [95% CI: 0.85-0.95]) (p-interaction = 0.0003). Assessment of the HCB-sex-smoking interaction suggested that the increased odds of SGA associated with HCB exposure was only in girls of smoking mothers (OR of 1.18 [95% CI: 1.11-1.25]) (p-interaction = 0.055). Higher concentrations of PFOA were associated with greater risk of SGA (OR of 1.64 [95% CI: 0.97-2.76]). Elevated PFOS levels were associated with increased odds of SGA in newborns of mothers who smoked during pregnancy (OR of 1.63 [95% CI: 1.02-2.59]), while an inverse association was found in those of non-smoking mothers (OR of 0.66 [95% CI: 0.61-0.72]) (p-interaction = 0.0004). No significant associations were found for p,p'-DDE.

CONCLUSIONS

Prenatal environmental exposure to organochlorine and perfluorinated compounds with endocrine disrupting properties may contribute to the prevalence of SGA. We found indication of effect modification by child's sex and smoking during pregnancy. The direction of the associations differed by chemical and these effect modifiers, suggesting diverse mechanisms of action and biological pathways.

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.

Effect of Iodine Nutrition on Pregnancy Outcomes in an Iodine-Sufficient Area in China

Many studies focused on the association between thyroid disease and pregnancy outcomes. The present study explored the effect of iodine nutrition during the first trimester on pregnancy outcomes. One thousand five hundred sixty-nine pregnant, euthyroid women at ≤12 weeks of gestation in an iodine-sufficient area in China were recruited. According to the World Health Organization (WHO) criteria for iodine nutrition during pregnancy, participants were divided into four groups: adequate iodine (median urinary iodine concentration (UIC), 150-249 μg/L), mild deficiency (UIC, 100-150 μg/L), moderate and severe deficiency (UIC, <100 μg/L), and more than adequate and excessive (UIC, ≥250 μg/L) groups. Pregnancy outcomes, including abortion, gestational hypertension, pre-eclampsia, gestational diabetes mellitus (GDM), placenta previa, placental abruption, preterm labor, low birth weight infants, macrosomia, breech presentation, and cord entanglement, were obtained during follow-up. The results showed that there was no significant difference in general characteristics, including age, body mass index, abdominal circumference, systolic blood pressure, diastolic blood pressure, heart rate, smoking rate, and drinking rate, among the four groups. In the more than adequate and excessive group, thyroid-stimulating hormone (TSH) was greater and free thyroxine (FT4) was lower than any other groups but still within normal range. The thyroglobulin (Tg) level was greater in the moderate and severe deficiency group. The incidence of GDM was significantly greater in women with mild iodine deficiency than in women with adequate iodine nutriture (18.38 vs. 13.70%, p < 0.05). Compared with the adequate group, incidence of macrosomia was significantly greater in the more than adequate and excessive group (12.42 vs. 9.79%, p < 0.05). Mild iodine deficiency was an independent risk factor for GDM (odds ratio = 1.566, 95% confidence interval = 1.060-2.313, p = 0.024); more than adequate and excessive iodine was an independent risk factor for macrosomia (OR = 1.917, CI = 1.128-3.256, p = 0.016). In summary, during 1st trimester, both mild iodine deficiency and excessive iodine intake had adverse impacts on pregnancy outcomes in an iodine-sufficient area.

The impact of isolated maternal hypothyroxinaemia on the incidence of large-for-gestational-age infants: the Ma'anshan Birth Cohort study

OBJECTIVE

The purpose of this study was to investigate whether isolated maternal hypothyroxinaemia (IMH) is associated with risks of small/large-for-gestational-age (SGA/LGA) infants.

DESIGN

Population-based prospective cohort study.

SETTING

Ma'anshan Maternal and Child Health (MCH) clinics, China.

POPULATION

Pregnant women with singleton births (n = 3178).

METHODS

Descriptive statistics were calculated for the demographic characteristics of the mothers and their newborns. Linear regression was applied to estimate the association between thyroid hormone levels and birthweight. Logistic regression was performed to calculate the association between IMH and SGA/LGA.

MAIN OUTCOME MEASURES

Outcomes included SGA/LGA.

RESULTS

The prevalence of IMH, defined as a free thyroxine value (FT4) lower than the 2.5th percentile with normal thyroid stimulating hormone, was 2.5% (78/3080) and 2.5% (74/2999) in the first and second trimesters, respectively. Additionally, 306 (9.6%) and 524 (16.5%) infants were defined as SGA and LGA, respectively. No evidence supported the notion that IMH is associated with an increased risk for SGA in either the first [odds ratio (OR): 1.762, 95% confidence interval (CI): 0.759-4.089] or the second (OR: 0.763, 95% CI: 0.231-2.516) trimester. However, an increased risk of LGA was observed among IMH women in the second trimester (OR: 2.088, 95% CI: 1.193-3.654). Maternal TPO-Ab positivity in the second trimester increased the risk of SGA (OR: 2.094, 95% CI: 1.333-3.290).

CONCLUSION

This study provides evidence that IMH is associated with LGA.

FUNDING

This work was supported by the National Natural Science Foundation of China (No. 81330068).

TWEETABLE ABSTRACT

Isolated maternal hypothyroxinaemia may increase the risk of large-for-gestational-age infants.

Maternal exposure to UV filters: associations with maternal thyroid hormones, IGF-I/IGFBP3 and birth outcomes

BACKGROUND

Several chemical UV filters/absorbers ('UV filters' hereafter) have endocrine-disrupting properties in vitro and in vivo. Exposure to these chemicals, especially during prenatal development, is of concern.

OBJECTIVES

To examine maternal exposure to UV filters, associations with maternal thyroid hormone, with growth factor concentrations as well as to birth outcomes.

METHODS

Prospective study of 183 pregnant women with 2nd trimester serum and urine samples available. Maternal concentrations of the chemical UV filters benzophenone-1 (BP-1) and benzophenone-3 (BP-3) in urine and 4-hydroxy-benzophenone (4-HBP) in serum were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The relationships between 2nd trimester maternal concentrations of the three chemical UV filters and maternal serum concentrations of thyroid hormones and growth factors, as well as birth outcomes (weight, height, and head and abdominal circumferences) were examined.

RESULTS

Positive associations between maternal serum concentrations of 4-HBP and triiodothyronine (T₃), thyroxine (T₄), insulin-like growth factor I (IGF-I) and its binding protein IGFBP3 were observed in mothers carrying male fetuses. Male infants of mothers in the middle 4-HBP exposure group had statistically significantly lower weight and shorter head and abdominal circumferences at birth compared to the low exposure group.

CONCLUSIONS

Widespread exposure of pregnant women to chemical UV filters and the possible impact on maternal thyroid hormones and growth factors, and on fetal growth, calls for further studies on possible long-term consequences of the exposure to UV filters on fetal development and children's health.

Prenatal exposure to mercury and longitudinally assessed fetal growth: Relation and effect modifiers

BACKGROUND

Prenatal mercury exposure has been related to reductions in anthropometry at birth. Levels of mercury have been reported as being relatively elevated in the Spanish population.

OBJECTIVE

To investigate the relation between prenatal exposure to mercury and fetal growth.

METHODS

Study subjects were pregnant women and their newborns (n:1867) participating in a population-based birth cohort study set up in four Spanish regions from the INMA Project. Biparietal diameter (BPD), femur length (FL), abdominal circumference (AC), and estimated fetal weight (EFW) were measured by ultrasounds at 12, 20, and 34 weeks of gestation. Size at and growth between these points were assessed by standard deviation (SD) scores adjusted for constitutional characteristics. Total mercury (T-Hg) was determined in cord blood. Associations were investigated by linear regression models, adjusted by sociodemographic, environmental, nutritional - including four seafood groups - and lifestyle-related variables in each sub-cohort. Final estimates were obtained using meta-analysis. Effect modification by sex, seafood intake and polychlorinated biphenyl (PCB) congener 153 concentration was assessed.

RESULTS

Geometric mean of cord blood T-Hg was 8.2μg/L. All the estimates of the association between prenatal Hg and growth from 0 to 12 weeks showed reductions in SD-scores, which were only statistically significant for BPD. A doubling of cord blood T-Hg was associated with a 0.58% reduction in size of BPD at week 12 (95% confidence interval -CI-: - 1.10, - 0.07). Size at week 34 showed estimates suggestive of a small reduction in EFW, i.e., a doubling of T-Hg levels was associated with a reduction of 0.38% (95% CI: - 0.91, 0.15). An interaction between PCB153 and T-Hg was found, with statistically significant negative associations of T-Hg with AC and EFW in late pregnancy among participants with PCB153 below the median.

CONCLUSIONS

Exposure to mercury during pregnancy was associated with early reductions in BPD. Moreover, an antagonism with PCB 153 was observed with noteworthy reductions late in pregnancy in AC and EFW in the group with lower PCB153.

Thyroid Function in Pregnant Women With Moderate to Severe Alcohol Consumption Is Related to Infant Developmental Outcomes

INTRODUCTION

Fetal alcohol spectrum disorders (FASD) have an estimated global prevalence of 2-5% of births, but prevalence is reported to be as high as 15.5% for FASD in certain high-risk communities in South Africa. Preclinical studies demonstrate that alcohol consumption during pregnancy interferes with thyroid hormone availability and function and negatively impacts exposed offspring. Very little is currently reported on this phenomenon in humans.

METHODS

This pilot study was embedded in the Drakenstein Child Health Study, a multi-disciplinary longitudinal birth cohort study investigating the early biological and psychosocial determinants of child health in South Africa. Twenty one mothers and their children with moderate-severe prenatal alcohol exposure (PAE) and 19 mothers and their children with no alcohol exposure were investigated. Maternal exposure history and blood samples were collected in mid-pregnancy and analyzed for serum-free thyroxin (FT4), free triiodothyronine (FT3), and thyroid stimulating hormone (TSH). Children were assessed with formally measured growth parameters and development was evaluated using the Bayley III Scales of Infant and Toddler Development (BSID III) at 6 and 24 months of age.

RESULTS

While there were no significant differences in serum TSH and FT4 between groups, FT3 levels were significantly higher in mothers with moderate-severe prenatal alcohol use. In abstinent pregnant women, levels of FT4 were significantly correlated with infants' scores on cognitive measures at 6 and 24 months of age and with levels of gross motor skills at 24 months. However, in mothers with alcohol use, FT4 levels were not correlated with any cognitive or motor skills, but FT3 levels were significantly associated with scores on children's social-emotional development at 24 months of age.

DISCUSSION

Thyroid function in PAE is sufficiently disrupted to lead to alterations in serum FT3 levels. The contrast in findings between PAE and abstinent dyads in their association of maternal thyroid function and infant development further suggests that such disruption is present and may contribute to adverse neurodevelopment. Further work is needed to determine the relationship between peripheral thyroid indices during pregnancy and neurodevelopmental outcomes in the context of PAE.

Comparative analysis of thyroid function parameters in pregnant women

The aim of the present study was to investigate the serum levels of free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) during pregnancy and comparative analysis of serum markers levels in non-pregnant women and pregnant women. Pregnant women were divided into four groups according to their gestational age: 8-14, 15-20, 21-36 and ≥37 weeks. Non-pregnant women were divided into three groups according to their age: 20-40, 41-55 and 56-85 years, and women of reproductive age (20-40 years) as control, which match their age and body mass index with pregnant women. The levels of serum markers were measured by magnetic microparticle chemiluminescence immunoassay and compared among different gestational weeks or with the control. In pregnant women, from 8-14 to ≥37 weeks, FT3 and FT4 levels declined, and significant differences were identified between each group, except for FT4 at 21-36 weeks, when compared with ≥37 weeks. While TSH was increased and significant differences were identified between each group. Compared with the control group, the concentrations of FT3, FT4 and TSH were lower in pregnant women for all weeks except for TSH in ≥37 weeks. Reference intervals of FT3, FT4 and TSH in pregnant women are much lower than that of the control women. Pregnant women are likely to have lower thyroid hormone levels throughout pregnancy. The current reference intervals of thyroid hormones were not feasible for pregnant women and pregnancy-specific reference intervals should be established according to a local Chinese pregnant women database.

Prepregnancy Hypothyroidism versus Gestational Hypothyroidism: A Comparative Study

INTRODUCTION

Hypothyroidism managed inadequately in pregnancy may have grave outcomes for both mother and baby. Understanding pregnancy outcomes in our country with low awareness about thyroid diseases is important.

OBJECTIVES

The objectives of the study were to evaluate demographic features and biochemical parameters in patients with prepregnancy hypothyroidism versus patients diagnosed to have primary hypothyroidism during pregnancy and to assess pregnancy outcomes.

STUDY DESIGN

Prospective design.

MATERIALS AND METHODS

The study was conducted in a tertiary care center in Bengaluru for 2 years. The patients were divided into two groups - Group I: Prepregnancy hypothyroidism and Group II: Hypothyroid during pregnancy. They were further staged according to ESI guidelines as subclinical or overt hypothyroidism.

STATISTICAL ANALYSIS

Chi-square and Mann-Whitney test.

RESULTS

A total of 452 pregnant women with hypothyroidism were analyzed. The data of 371 delivered pregnancies were available. Group I and II had 196 (43.36%) and 256 (56.64%) patients, respectively. Age at presentation (years) was 27.09 ± 4.19 in Group I versus 25.74 ± 4.29 in Group II (P = 0.003); gestational age (weeks) was 9.04 ± 5.41 in Group I versus 13.81 ± 9.12 in Group II (P = 0.000). There was one case of congenital hypothyroidism in baby in each group. Mean birth weight was 2.90 ± 0.39 kg in Group I versus 2.88 ± 0.36 kg in Group II; P = 0.608. There were four abortions in Group I versus ten in Group II (P = 0.231), 104 cesarean sections in Group I compared to 133 in Group II; (P = 0.382). There was no difference in number of cesarean sections, abortions and low birth weight babies between overt and subclinical hypothyroidism subgroups.

CONCLUSIONS

Group I patients presented earlier for testing suggesting awareness was good in this group. There was no difference in pregnancy outcome between the two groups. Overt versus subclinical status did not have any different effects on pregnancy outcomes in any group.

Association between exposure to organochlorine compounds and maternal thyroid status: Role of the iodothyronine deiodinase 1 gene

INTRODUCTION

Exposure to organochlorine compounds (OCs) may interfere with thyroid hormone (TH) homeostasis. The disruption of the deiodinase (DIO) enzymes has been proposed as a mechanism of action.

AIM

To evaluate the association between exposure to OCs and TH status in pregnant women, as well as to explore the role of genetic variations in the DIO1 and DIO2 genes.

METHODS

The study population (n=1128) was composed of pregnant women who participated in the INMA Project (Spain, 2003-2006). Hexachlorobenzene (HCB), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (4,4´-DDE), b-hexachlorocyclohexane (b-HCH), polychlorobiphenyl (PCB) congeners 138, 153 and 180, thyroid stimulating hormone (TSH), total triiodothyronine (TT3) and free thyroxine (FT4) were measured in serum samples taken during the first trimester of pregnancy (mean [standard deviation (SD)]: 13.5 [2] weeks of gestation). Polymorphisms in DIO1 (rs2235544) and DIO2 (rs12885300) were genotyped in maternal DNA. Sociodemographic and dietary characteristics were obtained by questionnaire.

RESULTS

A 2-fold increase in HCB was associated with lower TT3 (% change=-1.48; 95%CI: -2.36, -0.60). Women in the third tertile for b-HCH had lower TT3 (% change=-3.19; 95%CI: -5.64, -0.67). The interactions between DIO1 rs2235544 and PCB153 and b-HCH were statistically significant. The inverse association between PCB153 and TT3 was the strongest among women with AA genotype. Women with CC genotype presented the strongest inverse association between b-HCH and FT4.

CONCLUSION

Exposure to HCB and b-HCH was associated to a disruption in maternal TT3. The DIO1 rs2235544 SNP modified the association between exposure to some of the OCs (specifically b-HCH and PCB153) and maternal thyroid hormone levels. These results strengthen the hypothesis that DIO enzymes play a role in explaining the disruption of thyroid hormones in relation to exposure to OCs.

Fetal Thyroid Function, Birth Weight, and in Utero Exposure to Fine Particle Air Pollution: A Birth Cohort Study

BACKGROUND

Thyroid hormones are critical for fetal development and growth. Whether prenatal exposure to fine particle air pollution (≤ 2.5 μm; PM_2.5) affects fetal thyroid function and what the impact is on birth weight in normal healthy pregnancies have not been studied yet.

OBJECTIVES

We studied the impact of third-trimester PM_2.5 exposure on fetal and maternal thyroid hormones and their mediating role on birth weight.

METHODS

We measured the levels of free thyroid hormones (FT₃, FT₄) and thyroid-stimulating hormone (TSH) in cord blood (n = 499) and maternal blood (n = 431) collected after delivery from mother-child pairs enrolled between February 2010 and June 2014 in the ENVIRONAGE birth cohort with catchment area in the province of Limburg, Belgium.

RESULTS

An interquartile range (IQR) increment (8.2 μg/m³) in third-trimester PM_2.5 exposure was inversely associated with cord blood TSH levels (-11.6%; 95% CI: -21.8, -0.1) and the FT₄/FT₃ ratio (-62.7%; 95% CI: -91.6, -33.8). A 10th-90th percentile decrease in cord blood FT₄ levels was associated with a 56 g decrease in mean birth weight (95% CI: -90, -23). Assuming causality, we estimated that cord blood FT₄ mediated 21% (-19 g; 95% CI: -37, -1) of the estimated effect of an IQR increment in third-trimester PM_2.5 exposure on birth weight. Third-trimester PM_2.5 exposure was inversely but not significantly associated with maternal blood FT₄ levels collected 1 day after delivery (-4.0%, 95% CI: -8.0, 0.2 for an IQR increment in third-trimester PM_2.5).

CONCLUSIONS

In our study population of normal healthy pregnancies, third-trimester exposure to PM_2.5 air pollution was associated with differences in fetal thyroid hormone levels that may contribute to reduced birth weight. Additional research is needed to confirm our findings in other populations and to evaluate potential consequences later in life.

Early Maternal Thyroid Function During Gestation Is Associated With Fetal Growth, Particularly in Male Newborns

BACKGROUND

Intrauterine growth patterns are influenced by maternal thyroid function during gestation and by fetal sex. It is unknown, however, whether the relationships between maternal thyrotropin (TSH) and free thyroxine (fT4) levels in early pregnancy and fetal growth outcomes are modified by fetal sex.

DESIGN

Data were obtained from a community-based cohort study of pregnant women living in Amsterdam (Amsterdam Born Children and Their Development study). TSH and fT4 levels were determined during the first prenatal screening at median 13 weeks (interquartile range, 12 to 14). Women with live-born singletons and no overt thyroid dysfunction were included (N = 3988). Associations between these maternal hormones and birth weight, small for gestational age (SGA), and large for gestational age (LGA) were analyzed separately for each sex.

RESULTS

After adjustments, 1 pmol/L increase in maternal fT4 levels was associated with a reduction in birth weight of 33.7 g (P < 0.001) in male newborns and 16.1 g (P < 0.05) in female newborns. Increased maternal fT4 was not associated with increased odds for SGA, but was associated with a decreased odds for LGA in boys [per 1 pmol/L; odds ratio (OR), 0.79; 95% confidence interval (CI), 0.69 to 0.90]. Maternal subclinical hypothyroidism in early pregnancy (TSH > 2.5 mU/L, 7.3%) was associated with increased odds for LGA in male newborns (OR, 1.95; 95% CI, 1.22 to 3.11).

CONCLUSION

Maternal fT4 in early pregnancy was observed to be inversely associated with birth weight, with a stronger relationship in males. Male infants also had increased odds for LGA in mothers with subclinical hypothyroidism. Sexual dimorphism appears to be present in the relationship between maternal thyroid metabolism and fetal intrauterine growth, with stronger associations in male infants.

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum

BACKGROUND

Thyroid disease in pregnancy is a common clinical problem. Since the guidelines for the management of these disorders by the American Thyroid Association (ATA) were first published in 2011, significant clinical and scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid disease in women during pregnancy, preconception, and the postpartum period.

METHODS

The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations. The guideline task force had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members.

RESULTS

The revised guidelines for the management of thyroid disease in pregnancy include recommendations regarding the interpretation of thyroid function tests in pregnancy, iodine nutrition, thyroid autoantibodies and pregnancy complications, thyroid considerations in infertile women, hypothyroidism in pregnancy, thyrotoxicosis in pregnancy, thyroid nodules and cancer in pregnant women, fetal and neonatal considerations, thyroid disease and lactation, screening for thyroid dysfunction in pregnancy, and directions for future research.

CONCLUSIONS

We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid disease in pregnant and postpartum women. While all care must be individualized, such recommendations provide, in our opinion, optimal care paradigms for patients with these disorders.

Longitudinal Profiles of Thyroid Hormone Parameters in Pregnancy and Associations with Preterm Birth

Introduction

Overt thyroid disease in pregnancy is associated with numerous maternal and neonatal complications including preterm birth. Less is known about the contribution of trimester-specific subclinical alterations in individual thyroid hormones, especially in late gestation, on the risk of preterm birth. Herein, we examined the associations between subclinical changes in maternal thyroid hormone concentrations (TSH, total T3, free and total T4), measured at multiple time points in pregnancy, and the odds of preterm birth in pregnant women without clinical thyroid disease.

Participants and Methods

Data were obtained from pregnant women participating in a nested case-control study of preterm birth within on ongoing birth cohort study at Brigham and Women’s Hospital in Boston, MA (N = 439; 116 cases and 323 controls). We measured thyroid hormones in plasma collected at up to four time points in pregnancy (median = 10, 18, 26, and 35 weeks). We used multivariate logistic regression models stratified by study visit of sample collection to examine associations. To reveal potential biological pathways, we also explored these relationships by obstetric presentation of preterm birth (e.g., spontaneous preterm delivery) that have been previously hypothesized to share common underlying mechanisms.

Results

In samples collected at median 10 and 26 weeks of gestation, we found inverse associations between FT4 and the odds of overall preterm birth (odds ratio [OR] = 0.57, 95% confidence interval (CI) = 0.33, 1.00; and OR = 0.53, 95% CI = 0.34, 0.84, respectively). Positive associations were detected for total T3 at these same time points (OR = 2.52, 95% CI = 1.20, 5.31; and OR = 3.40, 95% CI = 1.56, 7.40, respectively). These effect estimates were stronger for spontaneous preterm birth.

Conclusions

Our results suggest that subclinical alterations in individual maternal thyroid hormones may influence the risk of preterm birth, and the strength of these associations vary by gestational age.

Multivariate Analysis of Thyrotropin in Preterm Newborns Based on Adequacy of Weight for Gestational Age

BACKGROUND

Different and conflicting data have been published concerning thyrotropin (TSH) levels among small-for-gestational-age (SGA) and appropriate-for-gestational-age (AGA) newborns. The hypothesis of this study was that SGA preterm infants have higher TSH levels than those who are not underweight do.

METHODS

This cross-sectional study analyzed the TSH levels of all preterm newborns with a negative congenital hypothyroidism screening result (TSH <7.5 μIU/mL). Secondary variables were sex, birth weight (SGA, AGA), days of life at blood extraction, maternal origin, gestational age, and being a twin or not. Two multiple linear regression models were constructed comparing TSH levels in SGA and AGA or the z-score for birth weight and the remaining variables.

RESULTS

A sample including 5819 preterm infants was obtained: 53.8% male, 23.3% twins, and 3.3% SGA. TSH concentrations were 2.16 ± 2.0 μIU/mL for the SGA infants and 1.80 ± 1.5 μIU/mL for the AGA infants (p = 0.012), with a negative correlation (p < 0.001) between TSH levels and the z-score for the weight of the newborn. The multivariate analysis comparing TSH levels between SGA and AGA gave the following: SGA (B = 0.46, p < 0.001), Latin American mother (B = -0.16, p = 0.029), days of life at blood extraction (B = -0.26, p < 0.001), and gestational age ≤28 weeks (B = -0.56, p < 0.001). Using the z-score for the weight, the associations were: maternal origin North Africa (B = 0.19, p = 0.042), days of life at blood extraction (B = -0.27, p < 0.001), gestational age ≤28 weeks (B = -0.55, p < 0.001), and z-score for weight (B = -0.12, p < 0.001).

CONCLUSIONS

Our multivariate analysis suggests that TSH concentrations are higher in SGA infants than they are in AGA infants, and this should be taken into account when establishing a reference interval appropriate for this population. The clinical relevance remains unknown, but lines of research are opened that may allow a better understanding of the long-term morbidities in these newborns.

Relationship between maternal hypoglycaemia and small-for-gestational-age infants according to maternal weight status: a retrospective cohort study in two hospitals

OBJECTIVE

The relationship between pre-pregnancy body mass index (BMI) and low glucose challenge test (GCT) results by maternal weight status has not been examined. This study aimed to clarify the relationship between a low GCT result and small for gestational age (SGA) by maternal weight status.

DESIGN

A retrospective cohort study in 2 hospitals.

SETTING

This study evaluated the obstetric records of women who delivered in a general community hospital and a tertiary perinatal care centre.

PARTICIPANTS

The number of women who delivered in both hospitals between January 2012 and December 2013 and underwent GCT between 24 and 28 weeks of gestation was 2140. Participants with gestational diabetes mellitus or diabetes during pregnancy, and GCT results of ≥140 mg/dL were excluded. Finally, 1860 women were included in the study.

PRIMARY AND SECONDARY OUTCOME MEASURES

The participants were divided into low-GCT (≤90 mg/dL) and non-low-GCT groups (91-139 mg/dL). The χ² tests and multivariate logistic regression analyses were conducted to investigate the association between low GCT results and SGA by maternal weight status.

RESULTS

The incidence of SGA was 11.4% (212/1860), and 17.7% (330/1860) of the women showed low GCT results. The patients were divided into 3 groups according to their BMI (underweight, normal weight and obese). When the patients were analysed separately by their weight status after controlling for maternal age, pre-pregnancy maternal weight, maternal weight gain during pregnancy, pregnancy-induced hypertension, thyroid disease and difference in hospital, low GCT results were significantly associated with SGA (OR 2.10; 95% CI 1.14 to 3.89; p=0.02) in the underweight group.

CONCLUSIONS

Low GCT result was associated with SGA at birth among underweight women. Examination of maternal glucose tolerance and fetal growth is necessary in future investigations.

The Effect of Subclinical Maternal Thyroid Dysfunction and Autoimmunity on Intrauterine Growth Restriction: A Systematic Review and Meta-Analysis

The objective of this study was to evaluate the association between maternal subclinical thyroid dysfunction and autoimmunity with the risk for intrauterine growth restriction (IUGR).Design is a systematic review and meta-analysis.A literature search was conducted using PubMed, Embase, and Cochrane database. A combination of 2 key words was used to search for the eligible studies: one indexed thyroid dysfunction or antithyroid antibodies; and the other one indexed the adverse neonatal outcomes of pregnancy, such as IUGR, small for gestational age, fetal growth restriction, or low birth weight.Two reviewers selected the studies, and eligible studies met the following criteria: prospective cohort studies or case control studies, studies of maternal thyroid dysfunction and positive antithyroid antibodies as the exposure of interest, and studies of IUGR or small for gestational age as the outcome of interest.Data were recorded, including data from maternal thyroid disorders and IUGR, and compared with a reference group.There were 22 individual data from the 13 cohort articles. Among these, 7 were focused on subclinical hypothyroidism (SCH), 4 on subclinical hyperthyroidism, 7 on positivity for thyroid peroxidase antibody (TPOAb), and 4 on isolated hypothyroxinemia. Meta-analysis showed that there was no effect of subclinical hyperthyroidism (odds ratio (OR) = 0.98; 95% confidence interval (CI), 0.40-2.41), TPOAb positivity (OR = 1.57; 95% CI, 0.77-3.18), or isolated hypothyroxinemia (OR = 1.05, 95% CI: 0.37-2.92) on IUGR. However, SCH is associated with IUGR (OR = 1.54; 95% CI, 1.06-2.25).SCH is associated with IUGR; however, subclinical hyperthyroidism, TPOAb positivity, or isolated hypothyroxinemia do not affect the risk of IUGR.

Prenatal Exposures to Multiple Thyroid Hormone Disruptors: Effects on Glucose and Lipid Metabolism

Background. Thyroid hormones (THs) are essential for normal human fetal development and play a major role in the regulation of glucose and lipid metabolism. Delivery of TH to target tissues is dependent on processes including TH synthesis, transport, and metabolism. Thyroid hormone endocrine disruptors (TH-EDCs) are chemical substances that interfere with these processes, potentially leading to adverse pregnancy outcomes. Objectives. This review focuses on the effects of prenatal exposures to combinations of TH-EDCs on fetal and neonatal glucose and lipid metabolism and also discusses the various mechanisms by which TH-EDCs interfere with other hormonal pathways. Methods. We conducted a comprehensive narrative review on the effects of TH-EDCs with particular emphasis on exposure during pregnancy. Discussion. TH imbalance has been linked to many metabolic processes and the effects of TH imbalance are particularly pronounced in early fetal development due to fetal dependence on maternal TH for proper growth and development. The pervasive presence of EDCs in the environment results in ubiquitous exposure to either single or mixtures of EDCs with deleterious effects on metabolism. Conclusions. Further evaluation of combined effects of TH-EDCs on fetal metabolic endpoints could improve advice provided to expectant mothers.

Maternal Thyroid Disease and Preterm Birth: Systematic Review and Meta-Analysis

CONTEXT

Thyroid disease in pregnancy is increasing with rising average maternal ages in developed countries. The evidence for an association between preterm birth and thyroid disease has been confounded by small studies with varying outcomes and methodology.

OBJECTIVE

The aim of this meta-analysis is to review the literature regarding thyroid disease including subclinical and overt hypothyroidism, hyperthyroidism, and isolated hypothyroxinemia and the specific outcome of preterm birth.

DATA SOURCES

A search of PubMed and Embase databases was performed in May 2015. A fixed-effects model was used to calculate the overall combined odds ratio (OR) with its corresponding 95% confidence interval (95% CI) to evaluate the relationship between thyroid disease and preterm delivery.

STUDY SELECTION

Studies were considered eligible if they met the following criteria: prospective cohort study or a case control study; the exposure of interest was maternal thyroid disease, including subclinical hypothyroidism, overt hypothyroidism, hyperthyroidism, or isolated hypothyroxinemia; the outcome of interest was preterm delivery; and data regarding numbers of preterm births in each cohort were reported.

DATA EXTRACTION

Data were recorded in a database evidence table including any incidence data for maternal thyroid disease and preterm birth compared to a reference group.

DATA SYNTHESIS

Fourteen cohort studies and one case control study involving 2 532 704 participants were included. The combined OR of preterm delivery for pregnant women with overt hypothyroidism compared with the reference group was 1.19 (95% CI, 1.12-1.26; P < .00001). There was also a significant risk of preterm birth in women with hyperthyroidism (OR, 1.24 [95%, CI 1.17-1.31]; P < .00001). Subclinical hypothyroidism and isolated hypothyroxinemia showed no significant increase in OR. Sensitivity analysis made no change to these results.

CONCLUSION

Both overt hypothyroidism and hyperthyroidism are associated with a small but statistically significant increase in OR for preterm birth not seen in subclinical hypothyroidism or isolated hypothyroxinemia.