Maternal thyroid function, prepregnancy obesity and gestational weight gain-The Generation R Study: A prospective cohort study

Burden, risk factors and outcomes associated with adequately treated hypothyroidism in a population-based cohort of pregnant women from North India

Hypothyroidism is the commonest endocrine disorder of pregnancy, with known adverse feto-maternal outcomes. There is limited data on population-based prevalence, risk factors and outcomes associated with treatment of hypothyroidism in early pregnancy. We conducted analysis on data from an urban and peri-urban low to mid socioeconomic population-based cohort of pregnant women in North Delhi, India to ascertain the burden, risk factors and impact of treatment, on adverse pregnancy outcomes- low birth weight, prematurity, small for gestational age and stillbirth. This is an observational study embedded within the intervention group of the Women and Infants Integrated Interventions for Growth Study, an individually randomized factorial design trial. Thyroid stimulating hormone was tested in 2317 women in early (9-13 weeks) pregnancy, and thyroxin replacement started hypothyroid (TSH ≥2.5mIU/mL). Univariable and multivariable generalized linear model with binomial family and log link were performed to ascertain risk factors associated with hypothyroidism and association between hypothyroidism and adverse pregnancy outcomes. Of 2317 women, 29.2% (95% CI: 27.4 to 31.1) had hypothyroidism and were started on thyroxin replacement with close monitoring. Overweight or obesity was associated with increased risk (adjusted RR 1.29, 95% CI 1.10 to 1.51), while higher hemoglobin concentration was associated with decreased risk (adjusted RR 0.93, 95% CI 0.88 to 0.98 for each g/dL) for hypothyroidism. Hypothyroid women received appropriate treatment with no increase in adverse pregnancy outcomes. Almost a third of women from low to mid socio-economic population had hypothyroidism in early pregnancy, more so if anemic and overweight or obese. With early screening and adequate replacement, adverse pregnancy outcomes may be avoided. These findings highlight the need in early pregnancy for universal TSH screening and adequate treatment of hypothyroidism; as well as for attempts to reduce pre and peri-conception overweight, obesity and anemia. Clinical trial registration: Clinical trial registration of Women and Infants Integrated Interventions for Growth Study Clinical Trial Registry-India, #CTRI/2017/06/008908; Registered on: 23/06/2017, (http://ctri.nic.in/Clinicaltrials/pmaindet2.php?trialid=19339&EncHid=&userName=society%20for%20applied%20studies).

Fluoride exposure and hypothyroidism in a Canadian pregnancy cohort

BACKGROUND

While fluoride can have thyroid-disrupting effects, associations between low-level fluoride exposure and thyroid conditions remain unclear, especially during pregnancy when insufficient thyroid hormones can adversely impact offspring development.

OBJECTIVES

We evaluated associations between fluoride exposure and hypothyroidism in a Canadian pregnancy cohort.

METHODS

We measured fluoride concentrations in drinking water and three dilution-corrected urine samples and estimated fluoride intake based on self-reported beverage consumption. We classified women enrolled in the Maternal-Infant Research on Environmental Chemicals Study as euthyroid (n = 1301), subclinical hypothyroid (n = 100) or primary hypothyroid (n = 107) based on their thyroid hormone levels in trimester one. We used multinomial logistic regression to estimate the association between fluoride exposure and classification of either subclinical or primary hypothyroidism and considered maternal thyroid peroxidase antibody (TPOAb) status, a marker of autoimmune hypothyroidism, as an effect modifier. In a subsample of 466 mother-child pairs, we used linear regression to explore the association between maternal hypothyroidism and child Full-Scale IQ (FSIQ) at ages 3-to-4 years and tested for effect modification by child sex.

RESULTS

A 0.5 mg/L increase in drinking water fluoride concentration was associated with a 1.65 (95 % confidence interval [CI]: 1.04, 2.60) increased odds of primary hypothyroidism. In contrast, we did not find a significant association between urinary fluoride (adjusted odds ratio [aOR]: 1.00; 95%CI: 0.73, 1.39) or fluoride intake (aOR: 1.25; 95%CI: 0.99, 1.57) and hypothyroidism. Among women with normal TPOAb levels, the risk of primary hypothyroidism increased with both increasing water fluoride and fluoride intake (aOR water fluoride concentration: 2.85; 95%CI: 1.25, 6.50; aOR fluoride intake: 1.75; 95%CI: 1.27, 2.41). Children born to women with primary hypothyroidism had lower FSIQ scores compared to children of euthyroid women, especially among boys (B coefficient: -8.42; 95 % CI: -15.33, -1.50).

DISCUSSION

Fluoride in drinking water was associated with increased risk of hypothyroidism in pregnant women. Thyroid disruption may contribute to developmental neurotoxicity of fluoride.

Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization

Thyroid dysfunctions are among the most common endocrine disorders and accurate biochemical testing is needed to confirm or rule out a diagnosis. Notably, true hyperthyroidism and hypothyroidism in the setting of a normal thyroid-stimulating hormone level are highly unlikely, making the assessment of free thyroxine (FT4) inappropriate in most new cases. However, FT4 measurement is integral in both the diagnosis and management of relevant central dysfunctions (central hypothyroidism and central hyperthyroidism) as well as for monitoring therapy in hyperthyroid patients treated with anti-thyroid drugs or radioiodine. In such settings, accurate FT4 quantification is required. Global standardization will improve the comparability of the results across laboratories and allow the development of common clinical decision limits in evidence-based guidelines. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. However, technical and implementation challenges, including the establishment of different clinical decision limits for distinct patient groups, still remain. Accordingly, different assays and reference values cannot be interchanged. Two-way communication between the laboratory and clinical specialists is pivotal to properly select a reliable FT4 assay, establish reference intervals, investigate discordant results, and monitor the analytical and clinical performance of the method over time.

Association between serum levels of TSH and free T4 and per- and polyfluoroalkyl compounds concentrations in pregnant women

Many per- and polyfluoralkyl substances (PFASs) may disrupt maternal thyroid hormone homeostasis in pregnancy. Concerns should be raised regarding the PFASs exposure in pregnant women because thyroid hormones are involved in the early development of the fetus. In this study, we measured the concentrations of 13 PFASs, including five novel short-chain PFASs, in serum from 123 pregnant women in Beijing, China. Linear regression models were used to investigate the association between thyroid-stimulating hormone (TSH) or free thyroxine (FT4) levels and PFASs concentrations under consideration of the impacts of pregnancy-induced physiological factors. We found that perfluorobutanoic acid (PFBA) (β=0.189, 95%CI=-0.039, 0.417, p=0.10) and perfluorodecanoic acid (PFDA) (β=-0.554, 95%CI=-1.16, 0.049, p=0.071) were suggestive of significant association with TSH in thyroid peroxidase antibody (TPOAb) negative women. No association was observed between all PFASs and FT4 levels after controlling for these confounding factors, such as BMI, gestational weight gain and maternal age. These findings suggest that it should pay more attention to the association between thyroid hormone levels and short-chain PFASs concentrations. Future studies could consider a greater sample and the inclusion of other clinical indicators of thyroid function, such as free T3 and total T3.

FTO and ADRB2 Genetic Polymorphisms Are Risk Factors for Earlier Excessive Gestational Weight Gain in Pregnant Women with Pregestational Diabetes Mellitus: Results of a Randomized Nutrigenetic Trial

Excessive gestational weight gain (GWG) is associated with increased risk of maternal and neonatal complications. We investigated obesity-related polymorphisms in the FTO gene (rs9939609, rs17817449) and ADRB2 (rs1042713, rs1042714) as candidate risk factors concerning excessive GWG in pregnant women with pregestational diabetes. This nutrigenetic trial, conducted in Brazil, randomly assigned 70 pregnant women to one of the groups: traditional diet (n = 41) or DASH diet (n = 29). Excessive GWG was the total weight gain above the upper limit of the recommendation, according to the Institute of Medicine guidelines. Genotyping was performed using real-time PCR. Time-to-event analysis was performed to investigate risk factors for progression to excessive GWG. Regardless the type of diet, AT carriers of rs9939609 (FTO) and AA carriers of rs1042713 (ADRB2) had higher risk of earlier exceeding GWG compared to TT (aHR 2.44; CI 95% 1.03–5.78; p = 0.04) and GG (aHR 3.91; CI 95% 1.12–13.70; p = 0.03) genotypes, respectively, as the AG carriers for FTO haplotype rs9939609:rs17817449 compared to TT carriers (aHR 1.79; CI 95% 1.04–3.06; p = 0.02).

Maternal adiposity, smoking, and thyroid function in early pregnancy

OBJECTIVE

A high activity of the deiodinase type 2 has been proposed in overweight, obese, and smoking pregnant women as reflected by a high triiodothyronine (T3)/thyroxine (T4) ratio. We speculated how maternal adiposity and smoking would associate with different thyroid function tests in the early pregnancy.

DESIGN

Cross-sectional study within the North Denmark Region Pregnancy Cohort.

METHODS

Maternal thyroid-stimulating hormone (TSH), total T4 (TT4), total T3 (TT3), free T4 (fT4), and free T3 (fT3) were measured in stored blood samples (median gestational week 10) by an automatic immunoassay. Results were linked to nationwide registers, and live-birth pregnancies were included. The associations between maternal adiposity (overweight or obese), smoking, and log-transformed TSH, fT3/fT4 ratio, and TT3/TT4 ratio were assessed using multivariate linear regression and reported as adjusted exponentiated β coefficient (aβ) with 95% CI. The adjusted model included maternal age, parity, origin, week of blood sampling, and diabetes.

RESULTS

Altogether 5529 pregnant women were included, and 40% were classified with adiposity, whereas 10% were smoking. Maternal adiposity was associated with higher TSH (aβ 1.13 (95% CI 1.08-1.20)), whereas maternal smoking was associated with lower TSH in the early pregnancy (0.875 (0.806-0.950)). Considering the T3/T4 ratio, both maternal adiposity (fT3/fT4 ratio: 1.06 (1.05-1.07); TT3/TT4 ratio: 1.07 (1.06-1.08)) and smoking (fT3/fT4 ratio: 1.07 (1.06-1.09); TT3/TT4 ratio: 1.10 (1.09-1.12)) were associated with a higher ratio.

CONCLUSIONS

In a large cohort of Danish pregnant women, adiposity and smoking showed opposite associations with maternal TSH. On the other hand, both conditions were associated with a higher T3/T4 ratio in early pregnancy, which may reflect altered deiodinase activity.

Assessing the Impact of Obesity on Pregnancy and Neonatal Outcomes among Saudi Women

Background: The rising prevalence of obesity has a significant impact on obstetrics practice regarding maternal and perinatal complications includes recurrent miscarriage, pregnancy-induced hypertension, preeclampsia, gestational diabetes, and prolonged labor. Objective: To assess the impact of obesity on pregnancy and neonatal outcomes among Saudi women. Methods: The study was conducted at King Abdul-Aziz Medical City, Jeddah. Design: A cross-sectional retrospective design. A total number of 186 participants were recruited from July to December 2018 according to eligibility criteria. The data were collected retrospectively by a review of the chart records of the labor and delivery department. Results: The mean (SD) age of participants was 31.94 (5.67) years old; two-thirds were in obesity class I. There was a significant association between obesity and pre-existing thyroid disease and induced hypertension class III. However, episiotomy showed that obesity class III was significantly different from obesity class II. Conclusion: This study concludes obesity affects the outcomes of pregnant Saudi associations between obesity and preeclampsia, perineal tears, and episiotomy variables, and other variables reflect no associations. Recommendations: Further studies are needed to generalize the results. This study endorses the pregnant women start the antenatal follow-up from 1st trimester so, the data will be available on the system for research.

Maternal thyroid disease and adiposity in mother and child

OBJECTIVE

Thyroid hormones are crucial developmental factors, and thyroid disease in pregnant women is a concern. Overweight and obesity are also important health concerns, and we hypothesized that in utero exposure to maternal thyroid disease could programme the foetus to development of adiposity.

DESIGN

Cohort and case-cohort studies.

PARTICIPANTS

Pregnant women from the Danish National Birth Cohort and their 7-year-old children.

MEASUREMENTS

Maternal thyroid disease (hyperthyroidism and hypothyroidism) was assessed from registrations of diagnoses and treatment (n = 71 706) or from the measurement of thyroid-stimulating hormone (TSH) in a stored blood sample from the early pregnancy (n = 7624). Maternal prepregnancy body mass index (BMI) and child BMI at 7 years of age were used to define overweight and obesity, and associations were evaluated using regression models adjusting for potential confounders.

RESULTS

No association was found between maternal thyroid disease in pregnancy and child overweight (hyperthyroidism: adjusted risk ratio (aRR): 1.02 (95% confidence interval (CI): 0.58-1.82); hypothyroidism: 1.31 (0.86-1.97)) or obesity (hyperthyroidism: 0.96 (0.53-1.75); hypothyroidism: 1.25 (0.76-2.05)). On the other hand, pregnant women with hypothyroidism in early pregnancy had a higher risk of being overweight (aRR: 1.20 (95% CI: 1.03; 1.41)) and obese (1.45 (1.07; 1.96)), whereas women with hyperthyroidism had a lower risk of being overweight (0.79 (0.64; 0.98)).

CONCLUSIONS

Results provide no evidence that maternal thyroid disease in pregnancy programmes adiposity in the child, but corroborate an association between maternal thyroid disease and adiposity in the mother.

Gestational weight gain and adverse pregnancy outcomes: a prospective cohort study

OBJECTIVE

To assess the associations of gestational weight gain (GWG) in early and late pregnancy with subsequent risks of adverse pregnancy outcomes in Chinese women.

DESIGN

Prospective cohort study.

SETTING

Shanghai, China.

PARTICIPANTS

We studied 2630 nulliparous singleton pregnant women with complete data on weight gain in early (≤17 weeks of gestation) and late (>17 weeks) pregnancy in the Shanghai Birth Cohort.

METHODS

GWG was standardised into z-scores by gestational age and categorised as low (z-score <-1), normal (-1 to +1) and high (>1). The adjusted relative risks (aRRs) and 95%CIs were estimated through log-binomial regression models. Interaction effects between GWG and some other adjustment factors were tested, further stratified analyses were performed separately where interaction terms were significant.

OUTCOME MEASURES

Adverse maternal and neonatal outcomes.

RESULTS

Independent from GWG in late pregnancy, higher GWG in early pregnancy was associated with higher risks of gestational diabetes mellitus (aRR: 1.66; 95% CI: 1.11 to 2.48), caesarean section (aRR: 1.21; 95% CI: 1.05 to 1.39) and prolonged hospitalisation (aRR: 1.56; 95% CI: 1.03 to 2.38). Higher GWG in late pregnancy was independently associated with higher risks of caesarean section (aRR: 1.24; 95% CI: 1.09 to 1.41), large for gestational age (aRR: 2.01; 95% CI: 1.50 to 2.7) and macrosomia (aRR: 1.90; 95% CI: 1.30 to 2.78). In addition, the risk of gestational hypertension increased significantly with increased total GWG (aRR: 1.78; 95% CI: 1.14 to 2.76). The effects of GWG in late pregnancy on maternal and neonatal outcomes were significantly different between the women bearing a female and the women bearing male fetus.

CONCLUSION

The GWG associations with adverse pregnancy outcomes differ at early and late pregnancy, and there may be effect modification by fetal sex in the association of GWG in late pregnancy with some pregnancy outcomes.

The Diverse Upper Reference Limits of Serum Thyroid-Stimulating Hormone on the Same Platform for Pregnant Women in China

OBJECTIVE

To describe the diverse upper reference limits of serum thyroid stimulating hormone on the same platform for pregnant women in China.

METHODS

The trimester-specific and population-specific TSH reference intervals for pregnant women were established, and then 5 reference intervals on the same platform in China were compared with the reference intervals derived from the present study and the manufacturer.

RESULTS

The most striking difference in the upper reference limits of TSH among 5 reference intervals on the same platform was shown at the first trimester of pregnancy. The calculated regional prevalence rates of subclinical thyroid diseases varied using the data derived from 30,771 pregnant women who visited the largest obstetric center in our district from 2008 to 2018.

CONCLUSION

We reported differences among 7 reference intervals of TSH on the same platform and showed the changing population factors significantly affected them.

CATS II Long-term Anthropometric and Metabolic Effects of Maternal Sub-optimal Thyroid Function in Offspring and Mothers

CONTEXT AND OBJECTIVES

The Controlled Antenatal Thyroid Screening Study I (CATS-I) was a randomized controlled trial investigating the effects of levothyroxine therapy for suboptimal gestational thyroid function (SGTF), comparing outcomes in children of treated (SGTF-T) with untreated (SGTF-U) women during pregnancy. This follow-up study, CATS-II, reports the long-term effects on anthropometric, bone, and cardiometabolic outcomes in mothers and offspring and includes a group with normal gestational thyroid function (NGTF).

DESIGN & PARTICIPANTS

332 mothers (197 NGTF, 56 SGTF-U, 79 SGTF-T) aged 41.2±5.3 years (mean±SD) and 326 paired children assessed 9.3±1.0 years after birth for (i) body mass index (BMI); (ii) lean, fat, and bone mass by dual-energy X-ray absorptiometry; (iii) blood pressure, augmentation index, and aortic pulse-wave-velocity; and (iv) thyroid function, lipids, insulin, and adiponectin. The difference between group means was compared using linear regression.

RESULTS

Offspring's measurements were similar between groups. Although maternal BMI was similar between groups at CATS-I, after 9 years (at CATS-II) SGTF-U mothers showed higher BMI (median [interquartile ratio] 28.3 [24.6-32.6] kg/m2) compared with NGTF (25.8 [22.9-30.0] kg/m2; P = 0.029), driven by fat mass increase. At CATS-II SGTF-U mothers also had higher thyroid-stimulating hormone (TSH) values (2.45 [1.43-3.50] mU/L) than NGTF (1.54 [1.12-2.07] mU/L; P = 0.015), since 64% had never received levothyroxine. At CATS-II, SGTF-T mothers had BMI (25.8 [23.1-29.8] kg/m2, P = 0.672) and TSH (1.68 [0.89-2.96] mU/L; P = 0.474) values similar to NGTF mothers.

CONCLUSIONS

Levothyroxine supplementation of women with SGTF did not affect long-term offspring anthropometric, bone, and cardiometabolic measurements. However, absence of treatment was associated with sustained long-term increase in BMI and fat mass in women with SGTF.

Interaction effect of obesity and thyroid autoimmunity on the prevalence of hyperthyrotropinaemia

PURPOSE

The role of thyroid autoimmunity in the association between obesity and hyperthyrotropinaemia remains unclear. We aimed to assess the relationship between obesity, autoimmunity, and hyperthyrotropinaemia.

METHODS

In this population-based cross-sectional study, 12531 Chinese individuals (18-80 years) with thyroid function test were categorized into three groups by body mass index (BMI) and were categorized into three layers by thyroid autoantibodies. Multivariate logistic regression was employed to assess the correlation and interaction effect.

RESULTS

There was no significant difference in prevalence of hyperthyrotropinaemia (P = 0.637) among three BMI groups. After stratification, the difference of serum thyrotropin (P < 0.01) and prevalence of hyperthyrotropinaemia (P < 0.01) between the three groups have significant linear trends at the positive levels of thyroid peroxidase antibody (TPOAb) or/and thyroglobulin antibody (TgAb). When TPOAb and TgAb were positive, the risk of hyperthyrotropinaemia increased 1.857-fold in overweight group and 2.201-fold in obese group compared with normal group. Compared with negative TPOAb and TgAb, the risk of hyperthyrotropinaemia for individuals with two positive antibodies increased 3.310-fold, 4.969-fold, and 5.122-fold in the three BMI groups. The adjusted OR (95% CI) for interaction were 1.033 (0.752-1.419) for overweight and one positive antibodies, 1.935 (1.252-2.990) for overweight and two positive antibodies, 1.435 (0.978-2.105) for obesity and one positive antibodies and 2.191 (1.252-3.832) for obesity and two positive antibodies.

CONCLUSION

Overweight and obesity were associated with hyperthyrotropinaemia only in presence of thyroid autoimmunity, and obesity might aggravate the pathogenic effect of autoimmunity on hyperthyrotropinaemia. There was an interaction effect between obesity and autoimmunity on the prevalence of hyperthyrotropinaemia.

Atmospheric Pollution and Thyroid Function of Pregnant Women in Athens, Greece: A Pilot Study

Exposure to air pollution and, in particular, to nitrogen dioxide (NO₂) or particulate pollutants less than 2.5 μm (PM2.5) or 10 μm (PM10) in diameter has been linked to thyroid (dys)function in pregnant women. We hypothesized that there may be a dose-effect relationship between air pollutants and thyroid function parameters. We retrospectively evaluated thyrotropin (TSH) in 293 women, NO₂, PM2.5 and PM10 levels in Athens. All the women were diagnosed with hypothyroidism for the first time during their pregnancy. Exposure to air pollution for each woman was considered according to her place of residence. Statistical analysis of age, pregnancy weight change, and air pollutants versus TSH was performed with ordinary least squares regression (OLS-R) and quantile regression (Q-R). A positive correlation for logTSH and PM2.5(r = +0.13, p = 0.02) was found, using OLS-R. Further analysis with Q-R showed that each incremental unit increase (for the 10th to the 90th response quantile) in PM2.5 increased logTSH(±SE) between +0.029 (0.001) to +0.025 (0.001) mIU/L (p < 0.01). The other parameters and pollutants (PM10 and NO₂) had no significant effect on TSH. Our results indeed show a dose-response relationship between PM2.5 and TSH. The mechanisms involved in the pathophysiological effects of atmospheric pollutants, in particular PM2.5, are being investigated.

The differences in the consumption of proteins, fats and carbohydrates in the diet of pregnant women diagnosed with arterial hypertension or arterial hypertension and hypothyroidism

Background

Excessive body weight induces the occurrence of arterial hypertension. The risk associated with irregularities during the perinatal period is increased in women with diagnosed hypothyroidism. Disorders of thyroid functions during pregnancy may cause higher body weight gains. The aim of this project was to determine the differences in the average daily intake of proteins, fats and carbohydrates in women with arterial hypertension and with hypothyroidism.

Methods

The control group (Group I) included healthy women. In this group, no complications during the course of pregnancy were observed and the delivery was on the due date. Group II was comprised of patients with arterial hypertension. Group III included patients with arterial hypertension, who were diagnosed with hypothyroidism before pregnancy. The women’s eating habits and dietary composition were analyzed based on a dietary assessment.

Results

Women with arterial hypertension (Group II) consumed the highest number of calories per day, while women with a normal pregnancy consumed the lowest amount of calories. The daily consumption of vegetable protein was similar in all study groups. The average daily consumption of fat, cholesterol and carbohydrates was the highest among women with diagnosed arterial hypertension. Women with arterial hypertension and hypothyroidism more frequently gave birth before the 38th week of pregnancy. The average daily intake of Arginine, Lysine, Methionine and Tryptophan was lower in the group of women with a normal pregnancy than in the two other groups.

Conclusions

Excessive calorie intake causing significant body weight gain fostered the occurrence of arterial hypertension during pregnancy.

Subclinical hypothyroidism in pregnancy

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Persistency of Thyroid Dysfunction from Early to Late Pregnancy

Background: Subclinical thyroid disease occurs in approximately 5-8% of all pregnancies and is associated with a higher risk of adverse outcomes such as miscarriage, preterm birth, and suboptimal child neurodevelopment. It is generally assumed that subclinical thyroid disease that persists from early to late pregnancy is associated with a higher risk of adverse outcomes than transient disease. However, it is unknown as to what percentage of women with subclinical disease during early pregnancy have persistent disease in the third trimester. Methods: This study comprised 42,492 mothers for whom early and late pregnancy thyrotropin (TSH), free thyroxine (fT4), triiodothyronine (T3), or TPOAbs were available and who did not receive thyroid treatment before or during pregnancy. We adjusted for potential confounders, including maternal age, parity, anthropometrics, and β-hCG concentrations. Results: Subclinical hypothyroidism and hypothyroxinemia persisted in 24.8% and 17.7% of cases. Overt hyperthyroidism persisted in 8.4% of cases while subclinical hyperthyroidism persisted in 20.9% of cases. Low T3 persisted in 43.4% of cases while elevated T3 persisted in 15.7% of cases. TPOAb positivity persisted in 84.0% of cases. In women with subclinical hypothyroidism, a TSH below ∼5 mU/L at the time of diagnosis was associated with an up to 50% lower risk of persistency. The fT4 concentration at diagnosis predicted hyperthyroidism persistency and TPOAb positivity predicted persistency of all disease entities. Conclusions: Early pregnancy thyroid disease only persists until the third trimester in 8.4-24.8% of cases when left untreated. The main predictor for persistency is TPOAb positivity, with TPOAb-positive women having a lower risk that subclinical hypothyroidism or hypothyroxinemia persists, but a higher risk that (subclinical) hyperthyroidism persists.

Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

BACKGROUND

Physiological changes in maternal thyroid function during pregnancy necessitate the use of pregnancy-specific reference ranges. Dynamic changes in thyrotropin (TSH) within the first trimester of pregnancy have been reported, but more evidence is needed to substantiate the findings. The objective of this study was to estimate pregnancy week-specific reference ranges for maternal TSH and free thyroxine (fT4) in early pregnancy.

METHODS

The study consecutively recruited serum residues from blood samples collected as part of the prenatal screening in the North Denmark Region, 2011-2015. TSH, fT4, thyroid peroxidase antibodies (TPOAb), and thyroglobulin antibodies (TgAb) were measured using an ADVIA Centaur XPT immunoassay. The reference cohort included 10,337 pregnant women who had no thyroid disease or other autoimmune diseases and were TPOAb- and TgAb negative. The main outcome measures were lower and upper reference limits (2.5th and 97.5th percentiles) for TSH and fT4 stratified by week of pregnancy.

RESULTS

Blood samples were drawn in pregnancy weeks 4-20 (median week 10), and 92% of the pregnancies ended with a live birth. TSH varied considerably in the first trimester of pregnancy, and the levels were highest in early pregnancy (weeks 4-6: 0.6-3.7 mIU/L) followed by a gradual decline to lower levels in weeks 9-11 (0.1-2.8 mIU/L) and 12-14 (0.03-2.8 mIU/L). Maternal fT4 showed less variation (weeks 4-6: 12-20 pmol/L; weeks 9-11: 13-21 pmol/L; weeks 12-14: 13-20 pmol/L).

CONCLUSIONS

The results corroborate dynamic week-specific changes in maternal TSH in early pregnancy. The use of uniform lower and upper reference limits for TSH in early pregnancy may be too simple.

Reference Intervals of Thyroid Hormones and Correlation of BMI with Thyroid Function in Healthy Zhuang Ethnic Pregnant Women

Ethnic differences in the level of thyroid hormones exist among individuals. The American Thyroid Association (ATA) recommends that an institution or region should establish a specific thyroid hormone reference value for each stage of pregnancy. To date, a limited number of studies have reported the level of thyroid hormones in Chinese minorities, and the exact relationship between BMI and thyroid function in pregnant women is ill. This study was performed to establish trimester-specific reference ranges of thyroid hormones in Zhuang ethnic pregnant women and explore the role of body mass index (BMI) on thyroid function. A total of 3324 Zhuang ethnic health pregnant women were recruited in this Zhuang population-based retrospective cross-sectional study. The values of thyroid stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were determined by automatic chemiluminescence immunoassay analyzer. Multivariate linear regression and binary logistic regression were constructed to evaluate the influence of BMI on the thyroid function. The established reference intervals for the serum thyroid hormones in three trimesters were as follows: TSH, 0.02–3.28, 0.03–3.22, and 0.08-3.71 mIU/L; FT4, 10.57–19.76, 10.05–19.23, and 8.96–17.75 pmol/L; FT3, 3.51–5.64, 3.42–5.42, and 2.93–5.03 pmol/L. These values were markedly lower than those provided by the manufacturers for nonpregnant adults which can potentially result in 6.10% to 19.73% misclassification in Zhuang pregnant women. Moreover, BMI was positively correlated with isolated hypothyroxinemia (OR=1.081, 95% CI=1.007–1.161), while the correlation between the BMI and subclinical hypothyroidism was not statistically significant (OR=0.991, 95% CI=0.917–1.072). This is the first study focusing on the reference ranges of thyroid hormones in Guangxi Zhuang ethnic pregnant women, which will improve the care of them in the diagnosis and treatment. We also found that high BMI was positively associated with the risk of isolated hypothyroxinemia.

Association of In Utero Persistent Organic Pollutant Exposure With Placental Thyroid Hormones

In utero exposure to persistent organic pollutants (POPs) can result in thyroid function disorder, leading to concerns about their impact on fetal and neonatal development. The associations between placental levels of various POPs and thyroid hormones (THs) were investigated. In a prospective Danish study initially established for assessing congenital cryptorchidism, 58 placenta samples were collected from mothers of boys born with (n = 28) and without (n = 30) cryptorchidism. The concentrations of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs), organotin chemicals (OTCs), organochlorine pesticides (OCPs), T4, T3, and rT3 were measured. The associations between placental THs and various POPs were analyzed using multiple linear regression. Five PBDEs, 35 PCBs, 14 PCDD/Fs, 3 OTCs, 25 OCPs, T4, T3, and rT3 were measured. No correlation between THs and the odds of cryptorchidism was found. Several POPs were significantly associated with THs: (1) T4 was inversely associated with BDEs 99, 100, ΣPBDE, and 2378-TeCDD, and positively associated with 1234678-HpCDF; (2) T3 was positively associated with 2378-TeCDF and 12378-PeCDF; and (3) rT3 was positively associated with PCB 81, 12378-PeCDF, and 234678-HxCDF, and inversely associated with tributyltin, ΣOTC, and methoxychlor. These results revealed that POP exposures were associated with TH levels in placenta, which may be a possible mechanism for the impacts of POP exposures on children's growth and development. This study provides new insight into the complexity of thyroid-disrupting properties of POPs. More research is needed to elucidate the biological consequences of POP exposures.