Evaluating the Progression to Hypothyroidism in Preconception Euthyroid Thyroid Peroxidase Antibody-Positive Women

Thyroid function testing prior to fertility treatment: will we ever agree?

Thyroid disorders are among the most prevalent of medical conditions, especially in women, with the prevalence of both hypo- and hyper-thyroidism being 10-fold more common in women than in men. Thyroid hormones play a key role in subfertility associated with ovulatory dysfunction and miscarriages. While overt thyroid disorders are more often clinically diagnosed, subclinical hypothyroidism (SCH) poses a particular challenge as these patients are usually asymptomatic while their risk for adverse outcomes is higher than in the general population. SCH is biochemically diagnosed when peripheral thyroid hormone levels are normal, but thyroid-stimulating hormone (TSH) levels are elevated; the condition may also be associated with thyroid autoimmunity (TAI). SCH and TAI may remain latent, asymptomatic or undiagnosed, but SCH can progress to overt hypothyroidism in women with TAI during ovarian stimulation and pregnancy. The lack of consensus on the upper limit of normal for TSH has led to variations in the diagnosis of SCH and therefore variations in thresholds for potential treatment. Consequently, there are variations in recommendations for routine testing in patients seeking fertility treatment. Guidance from the British Thyroid Association, American Thyroid Association (ATA), European Thyroid Association (ETA), and Royal College of Obstetrics and Gynaecology recommends screening using TSH with or without antibody testing while those from the National Institute for Health and Care Excellence and the latest from the American Society of Reproductive Medicine do not recommend routine testing. This paper outlines the discourse and varied recommendations related to routine thyroid function testing, with specific reference to the subfertile population of women, and highlights the discord in opinions that currently exist in this arena. An update of the ATA guideline, which will include women with subfertility and will be endorsed by multiple international bodies (including ESHRE and ETA), is eagerly anticipated.

Subclinical hypothyroidism in pregnancy: an evolving and controversial landscape

PURPOSE OF REVIEW

This review aims to elucidate the developments in subclinical hypothyroidism (SCH) in pregnancy effects, management, and treatment. While mostly focusing on recent research, landmark studies are briefly reviewed to highlight major developments since their publication.

RECENT FINDINGS

Research has continued to show an increased risk of adverse outcomes in pregnant women with SCH, with recent research showing an increased risk of both impaired glucose tolerance and hypertensive disorders of pregnancy. Research has continued to show unclear effects of SCH on neonatal outcomes, specifically in offsprings' intellectual development and ability. The benefit of treatment of SCH continues to be unclear; however, data suggest that treatment for thyroid stimulating hormone (TSH) 2.5-4 mU/l regardless of thyroid peroxidase antibodies status and TSH 4-10 mU/l in later pregnancy has not shown maternal or neonatal benefit.

SUMMARY

With varying guidelines and inconsistent research outcomes, it is not surprising that SCH practices differ widely. Further research, with uniform definitions and criteria of SCH, is needed to elucidate the optimal management and treatment of this common pregnancy condition. Additionally, further research specifically aimed at optimizing TSH in preconception and early pregnancy is needed.

Modifying effects of prenatal exposure to rare earth elements on birth outcomes through maternal thyroid function in early pregnancy

The potential health effects of exposure to rare earth elements (REEs) remain largely unexplored. This prospective cohort study aimed to elucidate the association between early pregnancy REE exposure and maternal thyroid function, as well as neonatal birth outcomes, in a cohort of pregnant women in Beijing, China. Additionally, the study explored the mediating role of thyroid homeostasis in the effects of REE exposure. Serum concentrations of fifteen REEs, along with Free Thyroxine (FT4), Thyroid Stimulating Hormone (TSH), and Thyroid Peroxidase Antibodies (TPOAb), were measured in 195 pregnant women. Multivariable linear regression analyses identified significant correlations between REE exposure and disruptions in maternal thyroid homeostasis. Specifically, Praseodymium (Pr) and Lutetium (Lu) were positively associated with FT4 levels, while Gadolinium (Gd) showed a positive correlation with TSH levels. Conversely, Thulium (Tm) was negatively associated with FT4 levels, and Yttrium (Y) was negatively correlated with TSH levels, indicating distinct interactions of specific REEs with thyroid regulation. Notably, Lu remained positively correlated with FT4 levels (β = 1.39, 95% CI = 0.55, 2.22) after adjusting for multiple comparisons. Regarding neonatal birth outcomes, Dysprosium (Dy) was found to be negatively associated with infant birth weight (β = -0.09, 95% CI = -0.170, -0.002). Furthermore, gender-specific analyses revealed significant associations between REE exposure and TPOAb levels among female neonates. Mediation analyses indicated that TSH significantly mediated the relationships between Terbium (Tb) and Y exposure and neonatal birth outcomes. The study suggests that REEs may disrupt endocrine function, particularly thyroid hormones, which could adversely affect neonatal growth, highlighting the need for further research on their impact in vulnerable populations.

Controversies in thyroid disease management in pregnancy

Adequate control of thyroid function is crucial for optimal pregnancy outcomes and neurodevelopment of the offspring, and testing for thyroid function is ideally performed using manufacturer- and gestation-specific reference ranges. While universal screening for thyroid dysfunction is not recommended, targeted case finding of women at risk of thyroid disease during pregnancy is advised. A number of controversies continue to fuel debate including: (i) the target range for thyroid stimulating hormone (TSH) in women with subfertility planning pregnancy, (ii) management of mild thyroid hypofunction before and during pregnancy, (iii) the treatment of thyroid peroxidase (TPO) antibody-positive euthyroid women with levothyroxine, (iv) the optimal choice of antithyroid treatment in women with hyperthyroidism. A significant body of evidence has accumulated in recent years, including large systematic reviews and meta-analyses of observational studies determining effects of thyroid dysfunction on pregnancy and fetal outcomes. In addition, outcomes from important randomised trials continue to inform current guidance on how to best care for women with thyroid dysfunction before and during pregnancy.

Effect of thyroid peroxidase antibody titers trajectories during pregnancy and postpartum on postpartum thyroid dysfunction

OBJECTIVE

To identify risk factors contributing to the development of postpartum hypothyroidism in women newly diagnosed with subclinical hypothyroidism (SCH) during the first trimester of pregnancy (T1). Additionally, this study aimed to explore the impact of thyroid peroxidase antibody (TPOAb) titers trajectories throughout pregnancy and postpartum.

METHODS

Thyroid hormone levels and thyroid autoantibody titers were collected from T1 to the 12th month postpartum. Logistic regression analysis was employed to identify independent risk factors for hypothyroidism at the 12th month postpartum and to develop a prediction model. Model performance was assessed through discrimination, calibration, and clinical applicability, with internal validation using the bootstrap resampling method. Growth Mixture Modeling was applied to delineate the trajectory of TPOAb titers during pregnancy and postpartum, and logistic regression analysis was conducted to investigate the influence of these trajectories on the occurrence of postpartum hypothyroidism.

RESULTS

At the 12th month postpartum, hypothyroidism was either newly diagnosed or persisted in 76 of 209 cases (36.36%). Several significant risk factors for postpartum hypothyroidism were identified, including multiparity, positive TPOAb in T1, positive TPOAb and thyroglobulin antibody in T1, serum thyroid-stimulating hormone levels at SCH diagnosis in T1, and the final dose of levothyroxine in the third trimester. A prediction model was constructed and presented with a nomogram. Furthermore, a higher trajectory of serum TPOAb titer during pregnancy and postpartum emerged as a predictive factor for hypothyroidism at the 12th month postpartum.

CONCLUSION

Women with elevated TPOAb titers during pregnancy and postpartum necessitate ongoing and vigilant monitoring of thyroid function, even after childbirth.

Subclinical Hypothyroidism and Thyroid Autoimmunity in Pregnancy: To Treat or Not to Treat

Subclinical hypothyroidism and thyroid autoimmunity in pregnancy are common conditions. They are both associated with adverse maternal and offspring outcomes. Women with thyroid autoimmunity should be monitored with regular thyroid function tests preconception and during gestation to identify women who develop hypothyroidism. The effectiveness of thyroid hormone treatment in reducing adverse outcomes in pregnancy has been studied in a number of randomized controlled trials. Current evidence shows obstetrical benefits of levothyroxine treatment in pregnant women with a thyroid-stimulating hormone level greater than 4 mU/L.

Use of levothyroxine for euthyroid, thyroid antibody positive women with infertility: Analyses of aggregate data from a survey of European thyroid specialists (Treatment of Hypothyroidism in Europe by Specialists: An International Survey)

OBJECTIVES

The use of levothyroxine (LT4) treatment aiming to improve fertility in euthyroid women with positive thyroid peroxidase antibodies (TPOAb) is not supported by the available evidence. The aim of the study was to document the use of LT4 by European thyroid specialists in such patients.

DESIGN

The data presented derive from Treatment of Hypothyroidism in Europe by Specialists, an International Survey (THESIS), a questionnaire conducted between 2019 and 2021 to document the management of hypothyroidism by European thyroid specialists. Here, we report the aggregate results on the use of LT4 in infertile, euthyroid women with positive TPOAb.

RESULTS

A total of 2316/5406 (42.8%) respondents stated that LT4 may be indicated in TPOAb positive euthyroid women with infertility. The proportion of those replying positively to this question varied widely across different countries (median 39.4, range 22.9%-83.7%). In multivariate analyses males (OR: 0.8; CI: 0.7-0.9) and respondents >60 years (OR: 0.7; 0.6-0.8) were the least inclined to consider LT4 for this indication. Conversely, respondents managing many thyroid patients ("weekly" [OR: 1.4; CI: 1.0-1.9], "daily" [OR: 1.8; CI: 1.3-2.4]) and practicing in Eastern Europe (OR: 1.5; CI: 1.3-1.9) were most likely to consider LT4.

CONCLUSIONS

A remarkably high number of respondents surveyed between 2019 and 2021, would consider LT4 treatment in TPOAb positive euthyroid women with infertility. This view varied widely across countries and correlated with sex, age and workload, potentially influencing patient management. These results raise concerns about potential risks of overtreatment.

Evaluating the progression to abnormal thyrotropin in euthyroid preconception women: a population-based study

BACKGROUND

Abnormal preconception thyrotropin levels were associated with fecundability and adverse fetomaternal outcomes, however, little is known regarding the natural change of serum thyrotropin in euthyroid preconception women. Thus, we performed a population-based study to evaluate the progression to abnormal thyrotropin in euthyroid preconception women.

METHODS

This retrospective cohort study used data from the National Free Prepregnancy Checkups Project (NFPCP) collected between 2010 and 2020. Female Han Chinese participants aged 20-49 years who had two repeated NFPCP participations with a time interval of 1.5-3.0 years, confirmed non-pregnant status within this duration, and normal thyrotropin levels during their first participation were included for the analysis of thyrotropin abnormalities during the second NFPCP examination. Data were analyzed between June 1 and October 1, 2023.

RESULTS

This study included 186,095 euthyroid women of reproductive age (mean ± SD, 26.72 ± 4.70 years) whose preconception thyrotropin levels were between 0.37 and 4.87 mIU/L. The median follow-up time was 2.13 (IQR, 1.85-2.54) years. A total of 8,497 (4.57%) women developed abnormal thyrotropin, including 4,118 (2.21%) subnormal thyrotropin and 4,379 (2.35%) supranormal thyrotropin. Compared with the reference group (thyrotropin 1.01-2.00 mIU/L), the lower baseline thyrotropin group had greater risk of developing subnormal thyrotropin, and the higher baseline thyrotropin group had greater risk of developing supranormal thyrotropin. Moreover, the restricted cubic spline analysis revealed a U-shaped dose-response association of baseline thyrotropin levels or thyrotropin multiples of the median (MOM) levels against risk of subnormal thyrotropin in the follow-up, and a J-shaped dose-response association against risk of supranormal thyrotropin levels in the follow-up. We further found that baseline thyrotropin outside of 1.43-1.93 mIU/L or baseline thyrotropin MOM outside 0.59-1.36 would hava a higher risk of developing of abnormal thyrotropin.

CONCLUSIONS

Both low and high baseline thyrotropin were associated with a significantly increased risk of developing abnormal thyrotropin outcomes. The optimal preconception baseline thyrotropin levels may be between 1.43 mIU/L and 1.93 mIU/L or baseline thyrotropin MoM between 0.59 and 1.36 to minimize progression toward abnormal thyrotropin after 1.5-3.0 years. These findings may help with counseling of preconception thyroid function monitoring.

Relationship between thyroid antibody levels and ovarian reserve function in infertile chinese women with normal thyroid-stimulating hormone

BACKGROUND

To analyze the relationship of thyroid peroxidase antibody and thyroid globulin antibody levels with ovarian reserve function in infertile women.

METHODS

The data of 721 infertile patients who visited the hospital from January 2019 to September 2022 and whose thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels were in the normal range, were retrospectively analyzed. These patients were divided into two sets of three groups-the negative group, the 2.6 IU/ml ~ 100 IU/ml group and the TPOAb > 100 IU/ml group according to the TPOAb (thyroid peroxidase antibody) level, or the TgAb (anti-thyroglobulin antibody) negative group, the 14.58 IU/ml ~ 100 IU/ml group and the TgAb > 100 IU/ml group according to the TgAb level. They were compared for differences in ovarian reserve function index and thyroid hormone levels and analyzed for the relationship among thyroid antibody levels, ovarian reserve function, and thyroid hormone levels.

RESULTS

When TSH > 2.5 mIU/L, the bFSH (basal follicle stimulating hormone) level in the TPOAb > 100 IU/ml group (9.10 ± 1.16 IU/L) was significantly higher than that in the TPOAb negative group (8.12 ± 1.97 IU/L) and the 2.6 IU/ml ~ 100 IU/ml group (7.90 ± 1.48 IU/L) (P < 0.05); when TSH ≤ 2.5 mIU/L, there were no statistically significant differences in the bFSH and AFC (antral follicle count) number at different TPOAb levels. Whether TSH ≤ 2.5 mIU/L or TSH > 2.5 mIU/L, there were no statistically significant differences in the bFSH and AFC number at different TgAb levels (P > 0.05). FT3/FT4 ratio in the TPOAb 2.6 IU/ml ~ 100 IU/ml group and the > 100 IU/ml group was significantly lower than in the negative group. FT3/FT4 ratio in the TgAb 14.58 ~ 100 IU/ml group and the > 100 IU/ml group was also significantly lower than in the TgAb negative group (P < 0.05). TSH level in the TPOAb > 100 IU/ml group was significantly higher than in the 2.6 ~ 100 IU/ml group and the TPOAb negative group, but there were no statistically significant differences among different TgAb groups.

CONCLUSIONS

When TPOAb > 100 IU/ml and TSH > 2.5 mIU/L, it may affect the ovarian reserve function in infertile patients, and the mechanism may be associated with increased TSH and the imbalance of FT3/FT4 ratio caused by the increase of TPOAb.