Effects of Thyroid Peroxidase Antibody on Maternal and Neonatal Outcomes in Pregnant Women in an Iodine-Sufficient Area in China

Thyroid Function Rather Than Thyroid Antibodies Affects Pregnancy and Perinatal Outcomes: Results of a Prospective Study

CONTEXT

Thyroid autoantibody positivity has been associated with an increased rate of obstetrical complications.

OBJECTIVE

We aimed to evaluate the role of thyroid autoantibodies in adverse pregnancy outcomes.

METHODS

This prospective study was conducted in the Endocrinology Unit of Pisa Hospital. A total of 975 pregnant women were studied from 2012 to 2021; 572 (59%) were diagnosed with autoimmune thyroid (AT) diseases; 403 (41%) served as controls. Levothyroxine (LT4) treatment was introduced when TSH was > 2.5 mIU/L in the AT group and when TSH was > 4 mIU/L in the controls. Rates of obstetrical complications in each group were measured.

RESULTS

Although the frequency of miscarriage in the AT group was greater (4.8%) than in the controls (2.9%), no significant differences were detected (P = 0.181). There were no differences between the 2 groups concerning the other pregnancy complications, and no association with the titer of thyroid antibodies was observed. The frequency of congenital malformations was greater in the AT group than in the controls (P = 0.019), but no correlation with major congenital malformations was detected (P = 0.872). Given that thyroid hormone concentrations were strictly controlled in our population, we documented a tendency (not significant) toward an increase in miscarriage and preterm birth among women with TSH > 4 mIU/L.

CONCLUSION

If thyroid function is adequately controlled, the presence and titer of thyroid autoantibodies does not negatively influence gestation. Although not significant, suboptimal thyroid hormone status seems to affect pregnancy outcomes more than thyroid autoimmunity.

An update on thyroid disorders in the postpartum period

PURPOSE

To review the pathophysiology, diagnosis and management of postpartum thyroid dysfunction, and related management of thyroid disorders during lactation.

METHODS

We reviewed the literature on postpartum thyroid dysfunction and management of thyroid disorders during lactation.

RESULTS

The postpartum period is characterized by a rebound from the immunotolerance induced by pregnancy. Routine thyroid function screening is not recommended for asymptomatic women in the postpartum period. Testing thyroid function should be considered at 6-12-week postpartum for high-risk populations, including women with a previous episode of postpartum thyroiditis, Graves' disease, or those with Hashimoto's thyroiditis on thyroid hormone replacement, known thyroid peroxidase antibody positivity, type 1 diabetes mellitus, other nonthyroidal autoimmune disease, or chronic hepatitis C. A serum TSH should also be checked in the setting of postpartum depression or difficulty lactating. If patients have thyrotoxicosis, new-onset or recurrent Graves' disease must be differentiated from postpartum thyroiditis, because the management differs. Periodic thyroid function testing is recommended following recovery from postpartum thyroiditis due to high lifetime risk of developing permanent hypothyroidism. Levothyroxine, and the lowest effective dose of antithyroid drugs, (propylthiouracil, methimazole, and carbimazole) can be safely used in lactating women. The use of radiopharmaceutical scanning is avoided during lactation and radioactive iodine treatment is contraindicated.

CONCLUSIONS

Diagnosing postpartum thyroid dysfunction is challenging, because symptoms may be subtle. A team approach involving primary care providers, endocrinologists, and obstetricians is essential for transitioning thyroid care from the gestational to the postpartum setting.

Neonatal Outcomes of Pregnancies Complicated by Maternal Hyperthyroidism

Objective

This study aimed to determine the proportion, clinical characteristics, hormonal status, median time for normalization of serum thyroxine (FT4) and thyroid-stimulating hormone (TSH) and factors affecting time to thyroid function test (TFT) normalization of neonates born to mothers with maternal hyperthyroidism admitted in our institution.

Methodology

This was a retrospective cohort study that included 170 newborns admitted to the Neonatal Intensive Care Unit (NICU) of Hospital Universiti Sains Malaysia (HUSM) with a history of maternal hyperthyroidism from January 2013 until December 2018. We analyzed their baseline demographic and clinical characteristics, maternal thyroid status and antibody levels. Finally, we analyzed newborn thyroid function and thyroid antibodies.

Results

The proportion of neonates born to mothers with maternal hyperthyroidism was 0.8% (170 of 20,198 neonates within the study period). Seven (4.1%) developed overt hyperthyroidism, while four (2.4%) had thyroid storm. The median time for thyroid function test normalization was 30 days (95% CI: 27.1 to 32.8). The median time for TFT normalization was longer among neonates of mothers with positive thyroid antibodies [46.6 days (95% CI, 20.6 to 39.4)] and of mothers who received anti-thyroid treatment [31.7 days (95% CI, 23.5 to 39.9)].

Conclusion

Neonates born to mothers with hyperthyroidism is uncommon. These babies were observed to have a longer time for normalization of thyroid function tests if their mothers had thyroid antibodies or received anti-thyroid treatment.

Variations in the Antithyroid Antibody Titre During Pregnancy and After Delivery

Background

Immunosuppression occurs during pregnancy, and the antithyroid antibody titre drops, rebounding after delivery. We aimed to determine variations in antithyroid antibody titres during pregnancy and after delivery.

Methods

This retrospective study was conducted in a single centre. Antibody titres of 142 patients were measured to assess variations in the levels of thyroid-stimulating hormone receptor antibodies (TRAbs), thyroid peroxidase antibodies (TPOAbs), and thyroid globulin antibodies (TgAbs). We compared the titres of each antibody between adjacent time periods (eg, first trimester (T1) vs second trimester (T2), T2 vs third trimester (T3), T3 vs the postpartum period (PP)) by paired t-test or the Wilcoxon test. Then, we analysed data from patients with complete laboratory examination results in all four periods with the Friedman test, performing comparisons among groups.

Results

In the TgAb group, significant differences existed between T1 and T2 and between T2 and T3 in the LT4 subgroup and between T1 and T2 in the no-medication subgroup. In the TRAb group, significant differences existed between T1 and T2 in the LT4 subgroup. In the TPOAb group, significant differences existed among each group in the LT4 subgroup, and there were significant differences between T1 and T2 and between T2 and T3 in the no-medication subgroup. The Friedman test showed that the P-values were 0.013 and 0.004 in the LT4 and no-medication subgroups of the TgAb group, respectively; 0.122 in the LT4 subgroup of the TRAb group; and <0.001 and 0.272 in the LT4 and no-medication subgroups of the TPOAb group, respectively. In the LT4 subgroup of the TgAb group, the P-values for comparisons of time periods were 0.602 between T1 and T2, 0.602 between T2 and T3, 0.006 between T1 and T3, and 0.602 between T3 and PP. In the no-medication subgroup of the TgAb group, the P-values were 0.078 between T1 and T2, 1.000 between T2 and T3, 0.011 between T1 and T3, and 0.078 between T3 and PP. In the LT4 subgroup of the TPOAb group, the P-values were 0.09 between T1 and T2, 0.014 between T2 and T3, <0.001 between T1 and T3, and 0.772 between T3 and PP.

Conclusion

We can conclude that the TgAb and TPOAb titres dropped during pregnancy.

Association of thyroid antibodies status on the outcomes of pregnant women with hypothyroidism (maternal hypothyroidism on pregnancy outcomes, MHPO-4)

Background

Autoimmunity increases with age and is often commonly evaluated in women of the reproductive age group. Prevalence of thyroid antibodies is common even in euthyroid pregnant women. We aim to compare the association of thyroid antibody status on the maternal and neonatal outcomes in pregnant women with hypothyroidism.

Methods

We conducted a cross-sectional retrospective study on 718 cases in the Aga Khan University Hospital. Information was collected on pregnant women who have been diagnosed with hypothyroidism before conception or during their antenatal period. Laboratory data were recorded for thyroid peroxidase antibodies, anti-thyroglobulin antibodies, and thyroid-stimulating hormone levels. Maternal and neonatal outcomes were also noted from medical file records. Data analysis was performed on Statistical Package for the Social Sciences version 20.0.

Results

Overall, 146 out 718 cases were included for final analysis. Thyroid peroxidase antibodies were positive in 66.4% and anti-thyroglobulin was positive in 52.1% cases, whereas 43.8% of cases had both antibodies positive. Pre-gestational diabetes was significantly associated with thyroid autoimmunity. There was a 73% less chance of gestational hypertension for thyroid autoimmune groups. Gestational diabetes and maternal (chronic) hypertension were found to have an independent effect on postpartum hemorrhage. Hypertensive disorders in pregnancy were found to have an independent risk for premature birth.

Conclusion

Our study reports a 74.7% prevalence of positive thyroid antibodies in hypothyroid pregnant women, with higher association with pre-gestational diabetes. Gestational hypertension was least likely to occur in thyroid autoimmune groups. None of the outcomes were independently associated with worse outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-03594-y.

Isolated maternal hypothyroxinemia and adverse pregnancy outcomes: A systematic review

Maternal thyroid hormones are vital for a normal pregnancy and the development of fetus and childhood; inadequate availability of thyroid hormones during pregnancy is associated with adverse pregnancy outcomes. Isolated maternal hypothyroxinemia (IMH) is defined as a low maternal T4 in the absence of TSH elevation. This systematic review aimed to investigate the association between IMH and adverse pregnancy outcomes. PubMed, Scopus and Web of science were searched for retrieving observational studies published up to September 2020, investigating the association of IMH with adverse pregnancy outcomes. From a total of 308 articles, 17 met our eligibility criteria and were used for the purpose of the present study. Definition of IMH varied in different studies. While some studies reported no adverse pregnancy outcomes for IMH, other studies found a positive association between first trimester IMH and feto-maternal outcomes including gestational hypertension, gestational diabetes, preterm delivery, fetal distress, small for gestational age, musculoskeletal malformations, spontaneous abortion, placental abruption and macrosomia. IMH, identified in the second trimester was associated with an increase in the risk of gestational diabetes, and hypertensive disorders of pregnancy in one study. There is no consensus on the adverse effects of IMH on pregnancy outcomes. Further comprehensive cohort studies using one standard definition for IMH, with large sample size and control of important confounders such as iodine status and maternal Thyroid peroxidase antibody (TPOAb) are needed for precise assessment of this association.

The Clinical Value and Variation of Antithyroid Antibodies during Pregnancy

Antithyroid antibodies, which include thyroid-stimulating hormone receptor antibodies (TRAbs), thyroid peroxidase antibodies (TPOAbs), and thyroid globulin antibodies (TgAbs), are widely known for their tight association with thyroid autoimmune diseases. The variation in all three kinds of antibodies also showed different trends during and after pregnancy (Weetman, 2010). This article reviewed the the physiological changes, while focusing on the variation of thyroid antibodies concentration in women during and after pregnancy, and adverse consequences related to their elevation. Since abnormal elevations of these antithyroid antibodies may lead to adverse outcomes in both mothers and fetuses, special attention must be paid to the titer of the antibodies during pregnancy. The molecular mechanisms of the variations in those antibodies have yet to be explained. The frequency and timing of thyroid antibody measurement, as well as different reference levels, also remain to be elucidated.

Management of overt hypothyroidism during pregnancy

Overt hypothyroidism is a common endocrine disorder affecting 1-2% of women of reproductive age. Optimizing treatment in pregnant women with overt hypothyroidism can reduce adverse fetal and maternal outcomes. Ideally, women who are known to have a history of hypothyroidism or those with risk factors for becoming hypothyroid, should have adequate preconception care to ensure euthyroidism from the onset of pregnancy, with a TSH target of below 2.5mIU/L. On women who are already on levothyroxine, an empirical dose increase of 30-50% as soon as pregnancy is confirmed may be considered. During pregnancy, levothyroxine doses should be titrated against TSH, which have trimester-specific ranges. In women who are known to be hypothyroid but are inadequately treated, we recommend a doubling of levothyroxine dose on at least three days a week to rapidly achieve euthyroidism. In newly diagnosed overt hypothyroidism in pregnancy, starting doses of either 100 or 150 mg daily may be considered safe.

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.

Implications of thyroid autoimmunity in infertile women with subclinical hypothyroidism in the absence of both goiter and anti-thyroid antibodies: lessons from three cases

There is a great deal of research interest regarding the underlying causes of slightly elevated TSH values in patients with subclinical hypothyroidism (SH) without abnormal findings on ultrasonography or anti-thyroid antibodies. Twelve infertile women with thyroglobulin antibody (TGAb) and thyroid peroxidase antibody (TPOAb)-negative nongoitrous SH were referred to our department of endocrinology between September 2007 and September 2015. None had been diagnosed with autoimmune thyroid disease or had any possible causes of SH. In all cases, LT4 was prescribed to bring TSH value below 2.5 mIU/L. Among those with infertility treatments, six (50%) became pregnant and gave birth to infants. Here, we report three of these six women who successfully became pregnant with infertility treatments and were found to have thyroid autoimmunity on data obtained during the postpartum period. Two developed postpartum thyroiditis, and the remaining one woman was temporarily weakly positive for TPOAb at 9 months postpartum. We describe three infertile subclinically hypothyroid women without goiter or anti-thyroid antibodies with potential thyroid autoimmunity. Thyroid autoimmunity is one of the most important issues for management of pregnant women, and thus, our findings are noteworthy for the care of infertile women with SH. This report provides valuable insights into the presence of autoimmunity in nongoitrous thyroid-associated antibody-negative SH patients.

Autoimmune thyroid disease during pregnancy

Understanding of changes in thyroid function and the consequences of thyroid disease during pregnancy has rapidly grown in the past two decades, and revised American Thyroid Association guidelines on this topic were published in 2017. This Review explores the association between thyroid autoimmunity and complications during and after pregnancy. Thyroid autoimmunity refers to the presence of antibodies to thyroperoxidase or thyroglobulin, or thyroid-stimulating hormone receptor antibodies (TRAbs), or a combination of these, and is present in up to 18% of pregnant women. Thyroid antibodies in pregnant women with normal functioning thyroids (ie, euthyroid) have been associated with several complications, including miscarriage and premature delivery. Treatments to improve pregnancy outcomes are being studied. Whether thyroid antibodies are associated with infertility and assisted reproductive technology outcomes is unclear; although, treatment with low doses of levothyroxine, which is usually used to treat hypothyroidism, can be considered in such situations. Additionally, thyroid antibodies have been associated with other neonatal and maternal complications. All these associations require confirmation in larger prospective studies, and their pathogenic mechanisms need to be better understood. Post-partum thyroiditis is substantially more frequent in women who have thyroid antibodies during pregnancy than in those who do not have thyroid antibodies; however, whether treatment can prevent post-partum thyroiditis in women who are or have been antibody positive is unknown. Finally, TRAbs cross the placenta from the mother to the fetus and can cause fetal or neonatal hyperthyroidism. Therefore, women who are positive for TRAbs during pregnancy should be monitored.

Thyroid autoantibodies in pregnancy are associated with hypertensive disorders of pregnancy: Ma'anshan Birth Cohort Study

OBJECTIVE

Hypertensive disorders of pregnancy (HDP) have been associated with adverse health outcomes for both mothers and children. Previous studies examining associations of maternal thyroid autoantibodies with HDP indicate conflicting results. The objective of this study was to examine associations of maternal thyroid autoantibody positivity in the first and the second trimesters with the risk of HDP.

DESIGN, PARTICIPANTS AND MEASUREMENTS

In the Ma'anshan Birth Cohort study, a population-based prospective study in China, a total of 3474 pregnant women were enrolled between May 2013 and September 2014. Thyroid autoantibodies, including antithyroperoxidase autoantibody (TPOAb) and antithyroglobulin autoantibody (TgAb), as well as thyroid function tests, were measured in both the first and the second trimesters in 2893 pregnant women. Multivariate logistic regression analyses were conducted to calculate the odds ratio (OR) and 95% confidence interval (CI) for the associations between thyroid autoantibodies and HDP.

RESULTS

Multivariate logistic regression analyses showed that TPOAb positivity in the first trimester was associated with a 1.80 (95% CI = 1.17-2.78) increased odds of HDP after adjustment for confounders, which was mainly due to an increased risk of gestational hypertension (OR = 1.93, 95% CI = 1.17-3.18). In addition, TgAb positivity in the first trimester was associated with a higher risk of HDP (OR = 1.78, 95% CI = 1.16-2.73) after adjustment for confounders, which was mainly due to an increased risk of gestational hypertension (OR = 1.89, 95% CI = 1.15-3.11). These associations were also seen among euthyroid women. Women with positive TPOAb in the second trimester seemed to have a higher risk of gestational hypertension (OR = 1.87, 95% CI = 1.02-3.43) after adjustment for confounders. However, among euthyroid women, TPOAb positivity in the second trimester was not associated with HDP. The TgAb status in the second trimester was not associated with HDP.

CONCLUSIONS

Our results show that TPOAb positivity and TgAb positivity in the first trimester are associated with an increased risk of HDP. These data demonstrate that these associations are even seen among euthyroid women.

Assessment of thyroid function in children, adults and pregnant and lactating women after long-term salt iodisation measurements

Universal salt iodisation (USI) has been successfully implemented in China for more than 15 years. Recent evidence suggests that the definition of 'adequate iodine' (100-199 µg/l) be revised to 'sufficient iodine' (100-299 µg/l) based on the median urinary iodine concentration (MUI) in school-age children. The objective of this study was to determine the prevalence of thyroid dysfunction in populations after long-term salt iodisation and examine whether the definition of adequate iodine can be broadened to sufficient iodine based on the thyroid function in four population groups. A cross-sectional survey was conducted in six provinces in the northern, central and southern regions of China. Four population groups consisting of 657 children, 755 adults, 347 pregnant women and 348 lactating women were recruited. Three spot urinary samples were collected over a 10-d period and blood samples were collected on the 1st day. In the study, among the adults, pregnant women and lactating women, the prevalence rates of elevated thyroglobulin antibody and thyroid microsomal antibody levels were 12·4, 8·5 and 7·8 %, and 12·1, 9·1 and 9·1 %, respectively. Abnormally high thyroid dysfunction prevalence was not observed after more than 15 years of USI in China because the thyroid dysfunction rates were all <5 %. The recommended range should be cautiously broadened from adequate iodine to sufficient iodine according to the MUI of school-age children considering the high levels of hormones and antibodies in the other populations. Adults, particularly pregnant women positive for thyroid antibodies, should be closely monitored.

Thyroid in pregnancy: From physiology to screening

Thyroid hormones are crucial for the growth and maturation of many target tissues, especially the brain and skeleton. During critical periods in the first trimester of pregnancy, maternal thyroxine is essential for fetal development as it supplies thyroid hormone-dependent tissues. The ontogeny of mature thyroid function involves organogenesis, and maturation of the hypothalamus, pituitary and the thyroid gland; and it is almost complete by the 12th-14th gestational week. In case of maternal hypothyroidism, substitution with levothyroxine must be started in early pregnancy. After the 14th gestational week, fetal brain development may already be irreversibly affected by lack of thyroid hormones. The prevalence of manifest hypothyroidism in pregnancy is about 0.3-0.5%. The prevalence of subclinical hypothyroidism varies between 4 and 17%, strongly depending on the definition of the upper TSH cutoff limit. Hyperthyroidism occurs in 0.1-1% of all pregnancies. Positivity for antibodies against thyroid peroxidase (TPOAb) is common in women of childbearing age with an incidence rate of 5.1-12.4%. TPOAb-positivity may be regarded as a manifestation of a general autoimmune state which may alter the fertilization and implantation processes or cause early missed abortions. Women positive for TPOAb are at a significant risk of developing hypothyroidism during pregnancy and postpartum. Laboratory diagnosis of thyroid dysfunction during pregnancy is based upon serum TSH concentration. TSH in pregnancy is physiologically lower than the non-pregnant population. Results of multiple international studies point toward creation of trimester-specific reference intervals for TSH in pregnancy. Screening for hypothyroidism in pregnancy is controversial and its implementation varies from country to country. Currently, the case-finding approach of screening high-risk women is preferred in most countries to universal screening. However, numerous studies have shown that one-third to one-half of women with thyroid disorders escape the case-finding approach. Moreover, the universal screening has been shown to be more cost-effective. Screening for thyroid disorders in pregnancy should include assessment of both TSH and TPOAb, regardless of the screening approach. This review summarizes the current knowledge on physiology of thyroid hormones in pregnancy, causes of maternal thyroid dysfunction and its effects on pregnancy course and fetal development. We discuss the question of case-finding versus universal screening strategies and we display an overview of the analytical methods and their reference intervals in the assessment of thyroid function and thyroid autoimmunity in pregnancy. Finally, we present our results supporting the implementation of universal screening.

Benign thyroid disease in pregnancy: A state of the art review

Thyroid dysfunction is the commonest endocrine disorder in pregnancy apart from diabetes. Thyroid hormones are essential for fetal brain development in the embryonic phase. Maternal thyroid dysfunction during pregnancy may have significant adverse maternal and fetal outcomes such as preterm delivery, preeclampsia, miscarriage and low birth weight. In this review we discuss the effect of thyroid disease on pregnancy and the current evidence on the management of different thyroid conditions in pregnancy and postpartum to improve fetal and neonatal outcomes, with special reference to existing guidelines on the topic which we dissect, critique and compare with each other. Overt hypothyroidism and hyperthyroidism should be treated appropriately in pregnancy, aiming to maintain euthyroidism. Subclinical hypothyroidism is often pragmatically treated with levothyroxine, although it has not been definitively proven whether this alters maternal or fetal outcomes. Subclinical hyperthyroidism does not usually require treatment and the possibility of non-thyroidal illness or gestational thyrotoxicosis should be considered. Autoimmune thyroid diseases tend to improve during pregnancy but commonly flare-up or emerge in the post-partum period. Accordingly, thyroid auto-antibodies tend to decrease with pregnancy progression. Postpartum thyroiditis should be managed based on the clinical symptoms rather than abnormal biochemical results.