Screening for hypothyroidism in pregnancy?

From the Guidelines

Screening for hypothyroidism should be performed in pregnant women with a history of thyroid dysfunction, family history of thyroid disease, symptoms of hypothyroidism, presence of goiter, autoimmune disorders, or history of head or neck radiation, as recommended by the American Association of Clinical Endocrinologists 1. The recommended screening test is measurement of thyroid-stimulating hormone (TSH) levels.

Key Points to Consider:

• The target TSH level during pregnancy is 0.1-2.5 mIU/L in the first trimester, and 0.2-3.0 mIU/L in the second and third trimesters.
• If TSH is elevated, free T4 levels should be checked.
• If both TSH is elevated and free T4 is low, treatment with levothyroxine should be initiated, with a starting dose typically of 1.0-2.0 mcg/kg/day, and adjustments made every 4-6 weeks based on TSH levels, as recommended by the JAMA study 1.
• Early detection and treatment of hypothyroidism in pregnancy is crucial because maternal thyroid hormones are essential for fetal brain development, especially in the first trimester, and untreated hypothyroidism can lead to adverse outcomes such as miscarriage, preterm birth, and impaired cognitive development in the child.

Additional Considerations:

• The American College of Obstetricians and Gynecologists recommends that physicians be aware of the symptoms and risk factors for postpartum thyroid dysfunction and evaluate patients when indicated 1.
• The American Academy of Family Physicians recommends against routine thyroid screening in asymptomatic patients younger than age 60 years, but notes that screening may be appropriate in high-risk or symptomatic individuals 1.
• The evidence for universal screening of all pregnant women is not sufficient to recommend for or against it, as stated in the JAMA study 1.

From the FDA Drug Label

For pregnant patients with pre-existing hypothyroidism, measure serum TSH and free-T4 as soon as pregnancy is confirmed and, at minimum, during each trimester of pregnancy. In pregnant patients with primary hypothyroidism, maintain serum TSH in the trimester-specific reference range The FDA recommends screening for hypothyroidism in pregnancy by measuring serum TSH and free-T4 as soon as pregnancy is confirmed and at least once per trimester. The goal is to maintain serum TSH within the trimester-specific reference range 2.

From the Research

Screening for Hypothyroidism in Pregnancy

• The prevalence of hypothyroidism in pregnancy is approximately 0.3-0.5% for manifest hypothyroidism and 4-17% for subclinical hypothyroidism 3
• Screening for thyroid dysfunction in pregnancy is crucial as hypothyroidism can lead to reduced neonatal and child neuropsychological development and maternal obstetric complications 4
• The case-finding approach of screening high-risk women is currently preferred in most countries, but numerous studies have shown that one-third to one-half of women with thyroid disorders escape this approach 3

Universal Screening vs. Targeted Screening

• Universal screening has been shown to detect two-times more thyroid disorders in early pregnancy than targeted high-risk case finding 5
• A study found that over half (55%) of pregnant women with abnormalities suggestive of autoimmune thyroiditis and/or hypothyroidism would be missed if only those with high-risk criteria were examined 5
• Another study found that hypothyroidism risk factors were present in 53.6% of patients, while in 46.4% there were none, indicating the necessity of carrying out screening tests in all pregnant women 6

Laboratory Diagnosis and Treatment

• Laboratory diagnosis of thyroid dysfunction during pregnancy is based upon serum TSH concentration, and results of multiple international studies point toward creation of trimester-specific reference intervals for TSH in pregnancy 3
• Screening for thyroid disorders in pregnancy should include assessment of both TSH and TPOAb, regardless of the screening approach 3
• Treatment of hypothyroidism in pregnancy typically involves levothyroxine intervention, and the target of thyroid function tests that responders aimed to achieve with l-T(4) was inconsistent among clinicians 7

Clinical Practice Variations

• A European survey found wide variation in clinical practice relating to the treatment and screening of hypothyroidism during pregnancy, including timing of screening, tests used, and criteria for starting treatment and monitoring 7
• Only 42% of responders or their institutions screened all pregnant women for thyroid dysfunction, while 43% performed targeted screening of only the high-risk group, and 17% did not carry out systemic screening 7