Decoding Thyroid Function Tests in Pregnancy

Pregnancy is a wonderful and exciting time, but it also comes with its own set of challenges and health considerations. One often overlooked area is thyroid health. Understanding thyroid function tests during pregnancy can play a crucial role in ensuring both maternal and baby’s health. This comprehensive guide will walk you through everything you need to know about thyroid function tests, their significance, and what you can do to maintain optimal thyroid health during this special time.

Why Thyroid Health Matters in Pregnancy

The thyroid gland plays a pivotal role in regulating metabolism, energy levels, and overall hormonal balance. During pregnancy, these functions become even more critical as the thyroid helps support fetal development and maintain maternal health. Unchecked thyroid dysfunction can lead to complications, making it essential to monitor thyroid function closely.

Understanding Thyroid Function Tests

Thyroid function tests involve several blood tests that assess the levels of thyroid hormones and related indicators. These tests include Thyroid-Stimulating Hormone (TSH), Free T4 (FT4), Total and Free T3 (FT3). Additionally, thyroid antibody tests may be conducted to check for autoimmune thyroid disorders.

The Importance of TSH Levels

TSH is the primary screening test for thyroid function. It measures how much thyroid-stimulating hormone is in your blood. During pregnancy, TSH levels are crucial for diagnosing both hypothyroidism and hyperthyroidism.

Reference Ranges for TSH During Pregnancy

In early pregnancy, TSH levels tend to be lower because of the influence of Human Chorionic Gonadotropin (hCG). Here are the trimester-specific TSH reference ranges:

First Trimester: 0.1-2.5 mIU/L
Second Trimester: 0.2-3.0 mIU/L
Third Trimester: 0.3-3.0 mIU/L

The Role of Free T4 and Total T4

Free T4 (FT4) is not reliable during pregnancy, so Total T4 (TT4) is measured often instead. TT4 levels increase by approximately 50% by the 16th week of pregnancy and remain elevated until delivery. This adaptation helps meet the increased metabolic demands of pregnancy.

FT3 in Pregnancy

FT3 or Total T3 (TT3) is usually measured only if there are abnormalities in TSH and T4 levels.

Who Should Get Tested?

Universal screening for thyroid dysfunction during pregnancy is not recommended. Instead, testing is advised for pregnant women who are at risk based on certain criteria:

Age over 30 years
More than two prior pregnancies
Current twin pregnancy
History of pregnancy loss, preterm delivery, or infertility
Type 1 diabetes or other autoimmune disorders
Morbid obesity (≥40kg/m2)
Personal or family history of thyroid disease
Known positive thyroid antibodies or presence of a goiter
Current use of levothyroxine

Managing Hypothyroidism

Diagnosing Hypothyroidism

Hypothyroidism is diagnosed when TSH levels are elevated and T4 levels are low. There are two types:

Subclinical Hypothyroidism: Elevated TSH but normal T4
Overt Hypothyroidism: Elevated TSH and low T4

Treatment Guidelines

For new onset subclinical hypothyroidism, monitoring or treatment with levothyroxine (LT4) may be recommended. Overt hypothyroidism requires immediate LT4 treatment to achieve a TSH level of ≤2.5 mIU/L in the first trimester and ≤3 mIU/L in subsequent trimesters. Regular thyroid function tests every 4-6 weeks help monitor and adjust the dosage.

Pre-existing Thyroid Disease

Women with pre-existing thyroid disease should have their thyroid function tested early in pregnancy, typically around 5-7 weeks gestation. Increased LT4 dosage may be necessary, with TSH levels monitored every 4-6 weeks.

Addressing Hyperthyroidism

Diagnosing Hyperthyroidism

Hyperthyroidism during pregnancy is often related to Graves’ disease. Diagnosis involves checking TSH, TT4, and Thyroid Receptor Antibodies (TRAb).

Managing Hyperthyroidism

Mild cases may only require monitoring, while more severe cases should be referred to a specialist for further management. Gestational transient thyrotoxicosis (GTT) may occur due to hCG effects and often resolves during pregnancy or after the first trimester.

Thyroid Antibodies During Pregnancy

Testing for thyroid antibodies (anti-TG or anti-TPO) is generally not recommended unless there is a history of infertility, pregnancy loss, or autoimmune thyroid disease. Positive antibodies indicate a higher risk of hypothyroidism and pregnancy loss.

Monitoring Positive Antibodies

Pregnant women with positive antibodies should be monitored for thyroid disease every 4-6 weeks. There is some evidence that LT4 treatment may reduce the risk of pregnancy loss in euthyroid women with positive antibodies, but this is not yet standard practice.

Take Away

Understanding and monitoring thyroid function during pregnancy is essential for the health of both mother and baby. If you fit any of the criteria for testing, it’s important to speak with a healthcare provider. For personalized thyroid health consultation, book an appointment with our naturopathic doctors at NMD Wellness of Scottsdale today.

By staying informed and proactive, you can ensure a healthier pregnancy and better outcomes for you and your baby.

Naturopathic Endocrinology - NMD Wellness of Scottsdale