Pregnancy & Thyroid Health: A Guide to the Updated Guidelines

Pregnant women need healthy thyroid levels for fetal development. According to the revised Korean Thyroid Association (KTA), guidelines for the diagnosis and management of thyroid disease guide doctors on how to manage thyroid concerns. Firstly, the acceptable range for a key hormone (TSH) is stricter in early pregnancy. Secondly, more women with borderline high TSH (subclinical hypothyroidism) will receive medication, even if other thyroid markers seem normal. Finally, treating women with normal thyroid function but thyroid antibodies is no longer recommended, as it might not help and could cause harm. These changes aim to catch and treat thyroid issues earlier, potentially improving pregnancy outcomes.

Key points:

• A new guideline for TSH levels: The revised Korean Thyroid Association (KTA) guidelines define the upper limit of TSH in the first trimester as 4.0 mIU/L.

• Subclinical hypothyroidism treatment: Levothyroxine treatment is recommended for pregnant women with TSH levels above 4.0 mIU/L (even if free T4 is normal), regardless of thyroid antibody status.

• Thyroid autoantibodies and normal thyroid function: Treating women with normal thyroid function and positive thyroid autoantibodies to prevent miscarriage is not recommended.

Background:

• Thyroid hormones are crucial for fetal development, especially brain and nervous system growth.

• Insufficient or excessive thyroid hormones during pregnancy can lead to complications like miscarriage, preterm birth, and preeclampsia.

• Thyroid autoimmunity (Hashimoto's thyroiditis, Graves' disease) is common in women, and antibodies may be linked to pregnancy complications regardless of thyroid function.

Changes in the KTA guidelines:

1. TSH range: Previously, the KTA used a single TSH range for all trimesters. The new guidelines acknowledge lower TSH levels in early pregnancy and set a specific upper limit of 4.0 mIU/L for the first trimester.

2. Subclinical hypothyroidism: Previously, treatment was only considered for TSH levels above 10 mIU/L. The new guidelines recommend treating women with TSH levels between 4.0 and 10.0 mIU/L (even if free T4 is normal) due to potential risks for the fetus.

3. Thyroid autoantibodies and normal thyroid function: Previously, some doctors treated women with positive thyroid autoantibodies and normal thyroid function to prevent miscarriage. The new guidelines advise against this practice due to a lack of evidence of benefits and potential risks of overtreatment.

Overall, the revised KTA guidelines aim to improve the diagnosis and management of thyroid disorders during pregnancy by:

• Identifying subclinical hypothyroidism earlier and offering treatment to potentially reduce pregnancy complications.

• Avoid unnecessary treatment for women with normal thyroid function and positive thyroid autoantibodies.

Navigating the intricacies of thyroid health during pregnancy is paramount to ensuring the well-being of both mother and baby. The guidelines set by the Korean Thyroid Association (KTA) play a pivotal role, and it's essential to understand how they have evolved over the years to provide the most accurate information for healthcare professionals and expecting mothers alike.

Evolution of Guidelines

The 2014 KTA guidelines saw a crucial shift by adopting the 2011 American Thyroid Association (ATA) guidelines for the TSH reference range during pregnancy. This decision was prompted by the absence of TSH data specific to Korean pregnant women at that time. According to these guidelines, the TSH reference range varies across trimesters, emphasizing the dynamic nature of thyroid function during pregnancy.

• First trimester: TSH range of 0.1 to 2.5 mIU/L

• Second trimester: TSH range of 0.2 to 3.0 mIU/L

• Third trimester: TSH range of 0.3 to 3.5 mIU/L.

Iodine Sufficiency in Korea

A pivotal study in 2018 by Kim et al. addressed not only TSH and free T4 levels but also urinary iodine concentrations in 417 pregnant women without thyroid autoantibodies. The results revealed that Korea stood as an iodine-sufficient country, with urinary iodine concentrations surpassing the adequate levels (397 to 451 µg/day). This underlines the importance of considering regional variations in iodine levels when establishing guidelines.

Debating Upper Limits

Table 1 presents a summary of TSH and free T4 data for each trimester, with notable findings. While both Moon et al. and Kim et al. reported an upper limit of the TSH reference range exceeding 4.0 mIU/L, the 2017 revised ATA guidelines recommended a fixed upper limit of 4.0 mIU/L in the absence of population-based data. A crucial turning point came with a subsequent study, post-2017, indicating that adverse pregnancy outcomes, including miscarriage and preterm delivery, did not increase when TSH levels were below 4.0 mIU/L. This revelation prompted a reevaluation of the upper limit, challenging the existing norms.

Subclinical Hypothyroidism and Overt Hypothyroidism

The revised KTA guidelines, considering the accumulating evidence, adopted 4.0 mIU/L as the upper limit of TSH in the first trimester. Beyond this threshold, a TSH level between 4.0 and 10.0 mIU/L, coupled with free T4 within the normal range, is classified as subclinical hypothyroidism. Notably, a TSH level surpassing 10 mIU/L is categorized as overt hypothyroidism, irrespective of the free T4 level. Navigating the nuances of thyroid health during pregnancy is a critical aspect of maternal care. The 2014 KTA guidelines set the stage, recommending levothyroxine (LT4) treatment for patients with a TSH level >2.5 mIU/L and a positive thyroid peroxidase antibody (TPOAb). However, the landscape shifted with the revised 2017 ATA guidelines, introducing complex criteria and raising questions about the strength of recommendations due to insufficient evidence.

Unraveling Post-2017 Research

After the release of the 2017 ATA guidelines, a surge of studies delved into the impact of LT4 treatment for subclinical hypothyroidism during pregnancy. A retrospective analysis of 5,405 pregnant women with TSH levels between 2.5 and 10 mIU/L revealed intriguing findings. Commencing LT4 treatment at 28 to 29 weeks reduced the risk of miscarriage by 38%, albeit with a 60% increase in premature births. Notably, when TSH levels ranged from 4.1 to 10.0 mIU/L, LT4 treatment significantly lowered the risk of miscarriage by 55%. However, this study left a critical gap by not specifying the presence of thyroid autoantibodies.

Prospective Insights into LT4 Treatment

A prospective study by Nazarpour et al. added depth to the discourse, focusing on 131 TPOAb-positive pregnant women with TSH levels between 2.5 and 10 mIU/L. The group receiving LT4 treatment experienced a 70% reduction in the risk of premature birth and an 83% reduction in neonatal admission compared to the untreated group. Strikingly, the effectiveness of LT4 treatment was correlated with TSH levels higher than 4.0 mIU/L. Similar observations were made in TPOAb-negative pregnant women, further emphasizing the potential benefits of LT4 treatment when TSH levels exceed 4 mIU/L.

RCTs and Neurocognitive Outcomes

Recent randomized controlled trials (RCTs) explored the impact of LT4 treatment on childhood neurocognitive outcomes. However, a meta-analysis of these trials indicated no positive effect on childhood IQ at ages 3 or 5. The timing of LT4 treatment, starting at 16.6 and 12 weeks of gestational age, raises questions about the window of effectiveness, considering fetal neurologic development initiates early in the first trimester.

Revised KTA Guidelines

In response to the evolving landscape, the revised KTA guidelines provide clear recommendations. When TPOAb is positive and TSH levels surpass 4 mIU/L, LT4 treatment is strongly endorsed. Notably, the guidelines remain silent on LT4 treatment when TSH levels fall between 2.5 and 4 mIU/L. For those with negative TPOAb, consideration of LT4 treatment is advised if TSH levels exceed 4 mIU/L. This shift from a weak to a strong recommendation reflects the emerging evidence and strengthens the guidance provided.

In the intricate landscape of pregnancy, thyroid health plays a pivotal role, with thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody emerging as key players. This article delves into the intricate connection between these antibodies and hypothyroidism, particularly those associated with Hashimoto's thyroiditis, unraveling their impact on pregnancy and the compelling research findings that shape our understanding.

Understanding the Prevalence

Between 5% to 14% of pregnant women test positive for TPOAb and 3% to 18% for thyroglobulin antibodies, underscoring the prevalence of these antibodies in the pregnant population. The presence of thyroid autoantibodies signifies a limited potential for increased thyroid hormone production during pregnancy, leading to elevated thyroid-stimulating hormone (TSH) levels and potential complications

Thyroid Autoantibodies and Pregnancy Complications

The correlation between thyroid autoantibodies and pregnancy-related complications is a subject of intense scrutiny. Spontaneous abortion, occurring before 20 weeks, is a significant concern, affecting 17% to 31% of pregnancies. Meta-analyses reveal a compelling relationship between thyroid autoantibodies and miscarriage. One study reported a pooled odds ratio of 2.55 (95% confidence interval [CI], 1.42 to 4.57), emphasizing the impact of these antibodies on pregnancy outcomes However, considerations about the age and average TSH levels of the subjects underscore the complexity of this association.

To Summarize

Key changes in the new KTA guidelines:

• Stricter TSH range in the first trimester: Now, the upper limit is 4.0 mIU/L, emphasizing early detection of potential issues.

• More women with borderline high TSH get treated: Even if other thyroid markers seem normal, those with TSH between 4.0 and 10.0 mIU/L might benefit from medication.

• No more treatment for normal thyroid function with thyroid antibodies: Treating women with normal thyroid function and positive antibodies to prevent miscarriage is no longer recommended due to lack of evidence and potential harm.

These changes aim to:

• Catch and treat thyroid issues earlier, potentially improving pregnancy outcomes.

• Avoid unnecessary treatment for women with normal thyroid function but thyroid antibodies.

The complex role of thyroid antibodies:

Thyroid antibodies, linked to Hashimoto's thyroiditis, are present in some pregnant women. While research is ongoing, the new KTA guidelines offer specific recommendations based on antibody presence and TSH levels.

Understanding the latest research:

Recent studies shed light on the effectiveness of treatment with levothyroxine (LT4) for subclinical hypothyroidism (slightly high TSH). The new KTA guidelines consider these findings:

• LT4 treatment for some TPOAb-positive women: If TSH exceeds 4 mIU/L and thyroid antibodies are present, LT4 treatment is strongly recommended.

• Treatment considered for TPOAb-negative women: For those without antibodies, LT4 might be recommended if TSH goes above 4 mIU/L.

Reference Article

1.Ahn, H. Y., & Yi, K. H. (2023). Diagnosis and Management of Thyroid Disease during Pregnancy and Postpartum: 2023 Revised Korean Thyroid Association Guidelines. Endocrinology and metabolism (Seoul, Korea), 38(3), 289–294. https://doi.org/10.3803/EnM.2023.1696

Related

https://healthnewstrend.com/unlocking-hypothyroidism-secrets-the-crucial-role-of-ft3-in-treatment

https://healthnewstrend.com/iodine-deficiency-in-hypothyroidism-a-new-perspective

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