Thyroid function reference ranges during pregnancy in a large Chinese population and comparison with current guidelines

Reference Intervals for Thyroid Hormones and Thyroid Volume in Children Aged 7 ~ 13 Years from Iodine-Sufficient Areas in Tianjin, China

Reference intervals (RIs) for serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) suitable for local children are urgently needed in northern China. The reference interval for thyroid volume (Tvol) in Chinese children also differed greatly from that recommended by the WHO. This study aimed to establish TSH, FT3, FT4, and Tvol RIs suitable for children in northern China. A total of 1070 children aged 7 ~ 13 were recruited from iodine nutrition-sufficient areas in Tianjin, China, from 2016 to 2021. Four hundred fifty-eight children aged 7 ~ 13 years, and 815 children aged 8 ~ 10 years were eventually included to study RIs for the thyroid hormones and Tvol. RIs for thyroid hormones were established in accordance with the Clinical Laboratory Standards Institute (CLSI) document C28-A3 guidelines. Quantile regression was used to analyze the influencing factors of Tvol. RIs for TSH, FT3, and FT4 were 1.23 (1.14 ~ 1.32) to 6.18 (5.92 ~ 7.26) mIU/L, 5.43 (5.29 ~ 5.52) to 7.89 (7.66 ~ 7.98) pmol/L, and 13.09 (12.85 ~ 13.73) to 22.22 (21.61 ~ 22.51) pmol/L. There was no need to establish RIs by age and gender. Our RIs could increase the prevalence of subclinical hyperthyroidism (P < 0.001) and reduce the prevalence of subclinical hypothyroidism (P < 0.001). Body surface area (BSA) and age are correlated with the 97th percentile of Tvol (both P < 0.001). Our reference interval could increase the goiter rate in children from 2.97 to 4.96% (P = 0.007). The thyroid hormones' reference intervals suitable for local children should be established. In addition, BSA and age should be considered when establishing Tvol reference interval.

ABC approach for the management of adults with hyperthyroidism: A practical strategy in primary care

Hyperthyroidism is commonly seen in primary care settings. However, the management of hyperthyroidism might be unclear to primary care doctors. Various guidelines have been published to assist clinicians in the management of thyroid disorders at various levels of care. The extensive coverage of these guidelines may not appeal to busy clinicians, and the guidelines do not focus on often resource-limited primary care settings. In this article, we aim to describe a practical guide for managing hyperthyroidism in primary care settings using an ABC approach.

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.

Gestational trimester-specific reference ranges for serum thyrotropin and free thyroxine in Japanese

Thyroid diseases in pregnant and lactating women may result in adverse outcomes for both mothers and infants. A reference range for thyroid function is required in different areas; however, few studies on the gestational change or reference ranges of thyrotropin (TSH) and free thyroxine (FT4) concentrations for Japanese pregnant women have been reported. To establish the gestational trimester-specific reference ranges of serum TSH and FT4 concentrations, our previously published data on 481 pregnant women with the mean age of 30.8 years who provided serum samples as early as gestational week (GW) 6 was compiled by using their percentile values. The overall median urinary iodine concentration (UIC) during pregnancy was 201 μg/L suggesting adequate iodine intake. The prevalence of positive serum thyroid autoantibody (ThAb), i.e., antithyroid peroxidase antibody (TPOAb) and antithyroglobulin antibody (TgAb), was 11.4%. The reference ranges (2.5-97.5th percentile) of serum TSH and FT4 concentration calculated for samples with negative TgAb and TPOAb were 0.04-6.06 mIU/L in the first trimester (T1), 0.31-3.11 mIU/L in the second trimester (T2) and 0.48-3.93 mIU/L in the third trimester (T3) for TSH, and 1.10-1.87 ng/dL (T1), 0.76-1.56 ng/dL (T2) and 0.76-1.14 ng/dL (T3) for FT4. Compared to published data around the world in the 2017 American Thyroid Association (ATA) guideline, both the upper and lower limits of our TSH and FT4 reference ranges in the first trimester were higher than those in other countries. Further research is necessary in larger samples.

Associations of Thyroid Function Tests with Lipid Levels and Adverse Pregnancy Outcomes During the First Trimester

OBJECTIVE

The present study aims to evaluate the relationship of thyroid function during the first trimester of pregnancy with lipid levels and pregnancy outcomes.

METHODS

Women who delivered babies at the Shanghai General Hospital between March 2019 and December 2019 with a known pregnancy outcome and complete data were included in the present study (n = 1779). A retrospective cohort study of all subjects with available first-trimester thyroid function testing and lipid levels data was conducted, and the relationship of thyroid function with lipid levels and pregnancy outcomes was evaluated. The data were analyzed using the SPSS software for statistical correlation.

RESULTS

The proportion of caesarean sections was higher in women with hypothyroxinemia (HIA) and hypothyroidism than in women with euthyroidism. Hypothyroidism was shown to be related with polyhydramnios, preterm labor and hypertriglyceridemia. HIA was correlated with increased rates of gestational diabetes mellitus (GDM), preeclampsia, gestational hypertension and hypertriglyceridemia. Compared with the euthyroidism group, the hypothyroidism group had a higher apolipoprotein A1 (Apo A1) level and apolipoprotein B level; the subclinical hypothyroidism group had a higher total cholesterol (TC) level and low-density lipoprotein cholesterol level; the HIA group had higher triglyceride, high-density lipoprotein cholesterol levels and lower TC, Apo A1 levels. TC levels were positively correlated with the thyroid-stimulating hormone level and negatively correlated with free thyroxine (FT4) level, and free triiodothyronine and FT4 levels were positively correlated with GDM occurrence.

CONCLUSION

Thyroid function in early pregnancy is associated with dyslipidemia and pregnancy outcomes; conventional screening of thyroid diseases in early pregnancy may help improve lipid levels and decrease adverse pregnancy outcomes.

Maternal thyroid function in multiple pregnancies - a systematic review

BACKGROUND

The function of the thyroid gland during pregnancy undergoes physiological changes to ensure the proper amount of thyroid hormones for both the pregnant woman and the fetus. Multiple pregnancies (MP) are characterized by specific differences compared to single pregnancies, e.g., higher concentrations of human chorionic gonadotropin, which also affect thyroid function. The aim was to collect available knowledge on maternal thyroid function in MP.

METHODS

We have systematically searched three databases: the PubMed/MEDLINE, Scopus and the Cochrane Library. The last search was run on the 4th of August 2022. We included full-text original observational and experimental studies written in English. Case reports, editorials, letters, conference abstracts, reviews and meta-analyses were excluded. No time criterion was established. Studies were considered eligible if at least one maternal thyroid function test was performed and reported. Studies on MP with a co-existing mole were excluded. The risk of bias was assessed with the use of the AXIS tool. The qualitative synthesis of evidence was applied.

RESULTS

The search strategy resulted in the identification of 821 manuscripts. After removing duplicates, we screened the titles and abstracts of 552 articles, out of which 57 were selected for full-text analysis. Finally, 12 articles were included in the review. They were conducted in 6 different countries and published between the years 1997 and 2022. The number of examined women with MP ranged from 9 to 1 626.

DISCUSSION AND CONCLUSIONS

Thyroid function differs between women with MP and SP. Scarce data are available on the topic, but MPs are most likely characterized by higher HCG levels, which influences thyroid-stimulating hormone and free thyroid hormone levels. These differences are mainly expressed in the 1st trimester of pregnancy. Separate population-based reference ranges are needed to correctly diagnose thyroid diseases in MP and to avoid unnecessary treatment. Further research is needed to fill the knowledge gaps.

Age- and sex-specific reference intervals for thyroid hormones in a Chinese pediatrics: a prospective observational study of 1,279 healthy children

BACKGROUND

Thyroid hormones are essential for early neurocognitive development and growth and development in childhood and adolescence. However, the reference intervals (RIs) for thyroid hormones in Chinese pediatric individuals remain unclear. This study aimed to establish thyroid hormone RIs for a Chinese pediatric population according to appropriate age- and sex-specific partitioning.

METHODS

In this prospective observational study, a total of 1,279 healthy children (singletons, aged from 1 day to 12 years) were recruited, and serum samples were analyzed on a Mindray automated chemiluminescence immunoassay analyzer CL-6000i for thyroid hormone detection, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (T3), and total thyroxine (T4). Age and sex-specific RIs were established, and the corresponding 95% confidence intervals (CIs) were calculated in accordance with the Clinical Laboratory Standards Institute (CLSI) document C28-A3 guidelines.

RESULTS

Quantile testing revealed that the median (P50) and RIs [2.5^th percentile (P2.5)-97.5^th percentile (P97.5)] for TSH, FT3, T3, and T4 of males differed significantly from those of females (P<0.05), except for FT4 (P=0.483). For FT3 and T3, the RIs of males were higher than that of females, and the RI of T4 for males was narrower and higher than that of females [P2.5-P97.5: 72.33-171.60 vs. 72.31-176.27 nmol/L; P50: 116.75 vs. 113.47 nmol/L, P=0.011]. RIs for TSH, FT3, FT4, T3, and T4 showed sex- and age-specific properties and displayed a wide variation during the first month of life but gradually narrowed and concentrated with increasing age. In addition, RIs of TSH, FT3, FT4, and T3 in males differed significantly from females in the first month of life (TSH: 1.46-10.87 vs. 1.08-11.35 mIU/L; FT3: 2.96-7.08 vs. 2.35-7.27 pmol/L, FT4: 13.34-28.65 vs. 13.82-31.83 pmol/L; T3: 0.83-2.33 vs. 0.72-2.46 nmol/L). The RI of T4 also exhibited a difference between males and females in the 9- to 12-year age group (59.31-150.72 vs. 63.29-146.94 pmol/L for males and females, respectively).

CONCLUSIONS

Pediatric RIs of thyroid hormones display age- and sex-specific trends. The RIs established in this study will improve the accuracy of TSH assay result interpretations and clinical decision-making in clinical laboratories that utilize the Mindray analytical platform.

Method-dependent variation in TSH and FT4 reference intervals in pregnancy: A systematic review

BACKGROUND

Gestational TSH and FT4 reference intervals may differ according to assay method, but the extent of variation is unclear and has not been systematically evaluated. We conducted a systematic review of published studies on TSH and FT4 reference intervals in pregnancy. Our aim was to quantify method-related differences in gestation reference intervals, across four commonly used assay methods, Abbott, Beckman, Roche and Siemens.

METHODS

We searched the literature for relevant studies, published between January 2000 and December 2020, in healthy pregnant women without thyroid antibodies or disease. For each study, we extracted trimester-specific reference intervals (2.5-97.5 percentiles) for TSH and FT4 as well as the manufacturer-provided reference interval for the corresponding non-pregnant population.

RESULTS

TSH reference intervals showed a wide range of study-to-study differences with upper limits ranging from 2.33 to 8.30 mU/L. FT4 lower limits ranged from 4.40 to 13.93 pmol/L, with consistently lower reference intervals observed with the Beckman method. Differences between non-pregnant and first trimester reference intervals were highly variable, and for most studies, the TSH upper limit in the first trimester could not be predicted or extrapolated from non-pregnant values.

CONCLUSIONS

Our study confirms significant intra- and intermethod disparities in gestational thyroid hormone reference intervals. The relationship between pregnant and non-pregnant values is inconsistent and does not support the existing practice in many laboratories of extrapolating gestation references from non-pregnant values. Laboratories should invest in deriving method-specific gestation reference intervals for their population.

The Interactive Effect of Prepregnancy Overweight/Obesity and Isolated Maternal Hypothyroxinemia on Macrosomia

CONTEXT

Prepregnancy overweight/obesity (OWO) and isolated maternal hypothyroxinemia (IMH) may increase the risk of macrosomia, but little is known about their potential combined effect on macrosomia.

OBJECTIVE

The aim of this study was to assess whether prepregnancy OWO and first-trimester IMH have a synergistic effect on the risk of macrosomia.

METHODS

A large prospective cohort study in a Chinese population from January 2016 to December 2018 in a tertiary care center. In total, 34 930 pregnant women were included. The main outcome measure was macrosomia.

RESULTS

A total of 34 930 participants comprising IMH and euthyroid cases was included in this study. Prepregnancy OWO and first-trimester IMH were independently associated with an increased risk of macrosomia (adjusted odds ratio [OR] 2.48, 95% CI 2.22, 2.78, and adjusted OR 1.65, 95% CI 1.34, 2.01, respectively). The coexistence of prepregnancy OWO and IMH was associated with macrosomia, with an adjusted OR of 5.26 (95% CI 3.9, 7.0) compared with pregnant women without either condition. The additive interaction between prepregnancy OWO and IMH was found to be significant with regard to macrosomia.

CONCLUSION

Prepregnancy OWO and IMH in the first trimester may synergistically increase the risk of macrosomia.

Antithyroid Peroxidase Antibodies and Histopathological Outcomes in Egyptian Patients Subjected to Total Thyroidectomy for Non-Malignant Nodular Goiter

Objective

The study aimed to assess antithyroid antibodies in patients with benign thyroid masses and the effect of total thyroidectomy on the antibodies titers.

Patients and Methods

This is a retrospective work of 112 cases managed with total thyroidectomy with positive antithyroid peroxidase antibodies (TPO-Ab), anti-thyroglobulin antibodies (Tg-Ab), or both. All patients were euthyroid before surgery. Thyroid function tests and thyroid antibodies levels were measured before and 6 and 12 months after surgery.

Results

Histopathological evaluation revealed Hashimoto thyroiditis (47.3%), colloid nodules (22.3%), and lymphocytic thyroiditis (30.4%). All patients were TPO-Ab positive, while 96 patients (85.7%) were Tg-Ab positive before surgery. There was no considerable change in TPO-Ab and Tg-Ab after surgery (p = 0.817, and p=0.560, respectively). Also, there was no significant difference between the three histopathological diagnoses in the levels of TPO-Ab (p = 0.086) or Tg-Ab (p = 0.673).

Conclusion

Antithyroid antibodies are not valuable markers for diagnosis or prognosis of benign thyroid diseases subjected to total thyroidectomy. We do not recommend their use beyond supporting evidence of the possibility of the autoimmune nature of the illness if other criteria are confirmed.

Supplemental iodine-containing prenatal multivitamins use and the potential effects on pregnancy outcomes in a mildly iodine-deficient region

PURPOSE

The use and contribution of prenatal multivitamins (PMV) as iodine source for pregnant women in China, especially in mildly iodine-deficient region, have not been well studied. This study aimed to explore the association between PMV intake during pregnancy and thyroid function in mothers and newborns.

METHODS

We performed a study involving women with a history of taking PMV during pregnancy between January 2013 and October 2015, in Shanghai, a mildly iodine-deficient region. Maternal thyroid function in early and late pregnancy, and neonatal TSH on postnatal d 3 were obtained from medical records. We compared the outcomes in pregnant women who took exclusively iodine-containing PMV (I + PMV) with those who took exclusively non-contained PMV (I- PMV). Propensity score matching (PSM) was used to identify women with similar baseline characteristics.

RESULTS

After PSM, 1280 women in I + PMV and 2560 in I- PMV had similar propensity scores and were included in the analyses. Introduction of I + PMV to women was associated with slightly higher maternal thyroid hormone production (higher maternal FT4, p = 0.01, non-significantly lower TSH, p = 0.79) and lower neonatal TSH levels (p < 0.0001). The frequency of adverse pregnancy outcomes or thyroid dysfunctions did not differ between groups in late pregnancy. Mothers received I + PMV (0.2 SD) had a stronger association of maternal TSH with neonatal TSH than those who received I- PMV (0.1 SD). These effects were only shown in TPOAb-negative mothers, not in TPOAb-positive mothers.

CONCLUSION

TPOAb-positive women display an impaired iodine transport in thyroid and placenta, and this may explain the lack of changes in maternal and neonatal thyroid parameters with I + PMV supplementation in these women. This phenomenon might suggest that these women require different iodine doses or treatment approach in comparison with TPOAb-negative women.

Pregnancy and Neonatal Outcomes With Levothyroxine Treatment in Women With Subclinical Hypothyroidism Based on New Diagnostic Criteria: A Systematic Review and Meta-Analysis

BACKGROUND

Subclinical hypothyroidism (SCH) during pregnancy has been associated with multiple adverse maternal and neonatal outcomes. However, the potential benefits of levothyroxine (LT4) supplementation remain controversial. Variations across studies in diagnostic criteria for SCH may, in part, explain the divergent findings on the subject. This study aimed to assess the effect of LT4 treatment on pregnancy and neonatal outcomes among pregnant women who were diagnosed as SCH based on the most recent diagnostic criteria.

METHODS

We conducted a systematic review and meta-analysis of the literature published from inception to January 2020. The search strategy targeted the studies on pregnancy and neonatal outcomes following LT4 treatment in women with SCH based on 2017 American Thyroid Association diagnostic criteria. Pooled effect sizes were estimated using fixed and random effect models, according to the absence or presence of heterogeneity which was assessed using the I-squared statistic. Sources of heterogeneity and the stability of results were evaluated through sensitivity analysis.

RESULTS

Of the 2781 identified references, 306 full-text articles were screened for eligibility. Finally, 6 studies including a total of 7955 participants were retained for analysis. Summary effect estimates indicated that pregnant women with SCH treated with LT4 had a lower risk of pregnancy loss [odds ratio (OR) = 0.55, 95% confidence interval (CI): 0.43-0.71], preterm birth (OR=0.63, 95% CI: 0.41-0.98) and gestational hypertension (OR = 0.78, 95% CI: 0.63-0.97) than those in control group.

CONCLUSION

LT4 treatment in pregnant women with SCH may reduce the risk of pregnancy loss, preterm delivery and gestational hypertension.

A Novel Nomogram for Predicting the Risk of Premature Delivery Based on the Thyroid Function in Pregnant Women

BACKGROUND

Maternal thyroid dysfunction and autoantibodies were associated with preterm delivery. However, recommendations for cutoff values of thyroperoxidase antibody (TPOAb) positivity and thyroid-stimulating homone (TSH) associated with premature delivery are lacking.

OBJECTIVE

To identify the pregnancy-specific cutoff values for TPOAb positivity and TSH associated with preterm delivery. To develop a nomogram for the risk prediction of premature delivery based on maternal thyroid function in singleton pregnant women without pre-pregnancy complications.

METHODS

This study included data from the International Peace Maternity and Child Care Health Hospital (IPMCH) in Shanghai, China, between January 2013 and December 2016. Added data between September 2019 and November 2019 as the test cohort. Youden's index calculated the pregnancy-specific cutoff values for TPOAb positivity and TSH concentration. Univariate and multivariable logistic regression analysis were used to screen the risk factors of premature delivery. The nomogram was developed according to the regression coefficient of relevant variables. Discrimination and calibration of the model were assessed using the C-index, Hosmer-Lemeshow test, calibration curve and decision curve analysis.

RESULTS

45,467 pregnant women were divided into the training and validation cohorts according to the ratio of 7: 3. The testing cohort included 727 participants. The pregnancy-specific cutoff values associated with the risk of premature delivery during the first trimester were 5.14 IU/mL for TPOAb positivity and 1.33 mU/L for TSH concentration. Multivariable logistic regression analysis showed that maternal age, history of premature delivery, elevated TSH concentration and TPOAb positivity in the early pregnancy, preeclampsia and gestational diabetes mellitus were risk factors of premature delivery. The C-index was 0.62 of the nomogram. Hosmer-Lemeshow test showed that the Chi-square value was 2.64 (P = 0.955 > 0.05). Decision curve analysis showed a positive net benefit. The calibration curves of three cohorts were shown to be in good agreement.

CONCLUSIONS

We identified the pregnancy-specific cutoff values for TPOAb positivity and TSH concentration associated with preterm delivery in singleton pregnant women without pre-pregnancy complications. We developed a nomogram to predict the occurrence of premature delivery based on thyroid function and other risk factors as a clinical decision-making tool.

Toward a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny - part I: which parameters from human studies are most relevant for toxicological assessments?

The 2018 European Food Safety Authority/European Chemicals Agency Guidance on the Identification of Endocrine Disruptors lacks clarity on how the presence or absence of substance-induced maternal thyroid hormone imbalance, or the potential for subsequent deleterious consequences in child neurodevelopment, should be established by toxicological assessments. To address these uncertainties, this narrative review evaluates human evidence on how altered maternal thyroid function may be associated with child neurodevelopmental outcomes; and seeks to identify parameters in human studies that appear most relevant for toxicological assessments. Serum levels of free thyroxine (fT4) and thyroid stimulating hormone (TSH) are most frequently measured when assessing thyroid function in pregnant women, whereas a broad spectrum of neurodevelopmental parameters is used to evaluate child neurodevelopment. The human data confirms an association between altered maternal serum fT4 and/or TSH and increased risk for child neurodevelopmental impairment. Quantitative boundaries of effects indicative of increased risks need to be established. Moreover, it is unknown if altered serum levels of total T4, free or total triiodothyronine, or parameters unrelated to serum thyroid hormones might be more relevant indicators of such effects. None of the human studies established a link between substance-mediated liver enzyme induction and increased serum thyroid hormone clearance, let alone further to child neurodevelopmental impairment. This review identifies research needs to contribute to the development of toxicity testing strategies, to reliably predict whether substances have the potential to impair child neurodevelopment via maternal thyroid hormone imbalance.

Subclinical thyroid dysfunction in the first trimester of pregnancy: 'Disease' versus physiological (pulsatile) variation in TSH concentrations

BACKGROUND

There is no universal consensus regarding cut-off points for TSH in pregnancy, so concentrations of 2.5 or 4.0 mIU/L were suggested for first trimester (Endocrine Society [2012] and ATA [2017] guidelines, respectively). Yet, the impact of physiological variation in TSH secretion has not been assessed.

SUBJECTS AND METHODS

We assessed baseline concentrations of free T4, free T3 and TSH at 30-minute intervals (between 7.00 and 9.00 hours) in 110 healthy pregnant women, age 30.2 ± 6.0 years, 9.9 ± 2.4 weeks of gestation, and in 19 female controls, age 28.9 ± 10.7.

RESULTS

Mean TSH concentrations in pregnant women were 1.62 ± 1.26 mIU/L and on average varied by 39.5% (dispersion between the highest and the lowest TSH), with no difference in TSH variation between pregnant women and controls. Taking into account the highest TSH out of five consecutive measurements, TSH >2.5 mIU/L and TSH above 4.0 mIU/L were found in 23 (20.9%) and 10 (9.1%) pregnant women, respectively. In contrast, when the lowest TSH value was considered, then concentrations of TSH >2.5 mIU/L and >4.0 mIU/L were found in 14 (12.7%) and 4 (3.6%) women, respectively. This discrepancy was even more pronounced in aTPO-negative subjects (21 [21.2%] vs 8 [8.1%] women, for TSH >2.5 mIU/L, and six [6.06%] vs one [1.01%], for TSH >4.0 mIU/L). Furthermore, either six (5.4%) or 10 (9.1%) women had TSH concentrations below 0.1 mIU/L.

CONCLUSIONS

In a significant number of patients, diagnosis of subclinical thyroid dysfunction could be erroneously made not as a result of 'disease', but as a result of physiological variation in TSH concentrations.

Perfluoroalkyl and polyfluroalkyl substances and maternal thyroid hormones in early pregnancy

BACKGROUND

The development of the embryo and fetal brain depends on maternal transfer of thyroid hormones (THs) in early pregnancy. Perfluoroalkyl and polyfluoralkyl substances (PFAS) may disrupt maternal TH homeostasis in pregnancy, but findings from epidemiologic studies were inconsistent. We aimed to assess this relationship in early pregnancy in a large prospective cohort study.

METHODS

A total of 1885 pregnant women enrolled in the Shanghai Birth Cohort were used. Ten PFAS, free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH) and thyroid peroxidase antibody (TPOAb) were measured in maternal blood collected prior to 16 weeks of gestation. Multiple linear regression accompanied by restricted cubic spline was used to examine the association and the exposure-response relationship between each PFAS and TH in separate models. Possible effect modification by TPOAb status was also investigated.

RESULTS

Perfluorooctanoic acid [PFOA, β = 0.121, 95% confidence interval (CI): 0.015, 0.227] and perfluorohexane sulfonate (PFHxS, β = 0.123, 95% CI: 0.024, 0.222) were positively associated with FT4. Perfluorononanoic acid (PFNA, β = 0.179, 95% CI: 0.047, 0.311) and PFHxS (β = 0.197, 95% CI: 0.054, 0.339) were positively associated with FT3, while PFHxS was negatively associated with TSH (β = -0.115, 95%CI: 0.216, -0.014). TPOAb-positivity appeared to modify the associations between PFAS and THs. In TPOAb-positive women, several long-chain PFAS were positively associated with FT4 and/or FT3 and tended to be negatively associated with TSH.

CONCLUSIONS

Several long-chain PFAS were associated with disrupted TH homeostasis in Chinese pregnant women, especially among TPOAb-positive women.