• Rationale and Comments

    Subclinical hypothyroidism is defined as an elevated serum TSH level in the presence of a normal free T4 level and is found in 2% to 5% of otherwise healthy pregnant women. Subclinical hypothyroidism is unlikely to progress to overt hypothyroidism during pregnancy. While some authorities and organizations have recommended routine screening for all pregnant women and subsequent treatment with levothyroxine, two recent, large (>100,000 women) prospective randomized clinical trials of screening and treatment for subclinical hypothyroidism demonstrated no effect of treatment on offspring IQ at age five years. Because treatment for subclinical hypothyroidism has not resulted in a beneficial effect on outcomes, routine screening for subclinical hypothyroidism is not currently recommended. Targeted screening for women at risk for overt hypothyroidism is still appropriate.

    Sponsoring Organizations

    • Society for Maternal-Fetal Medicine


    • Randomized controlled trials


    • Endocrinologic
    • Obstetrical


    • Thyroid disease in pregnancy. Practice Bulletin No. 148. American College of Obstetricians and Gynecologists. Obstet Gynecol. 2015;125:996-1005.
    • Lazarus JH, Bestwick JP, Channon S, Paradice R, Maina A, Rees R, et al. Antenatal thyroid screening and childhood cognitive function [published erratum appears in N Engl J Med. 2012;366:1650]. N Engl J Med. 2012;366:493-501.
    • Society for Maternal-Fetal Medicine. Screening for thyroid disease during pregnancy. Contemporary OB/GYN; August 2012. https://www.smfm.org/publications/88-screening-for-thyroid-disease-in-pregnancy