Variation in Treatment Practices for Subclinical Hypothyroidism in Pregnancy: US National Assessment

Context: Although thyroid hormone replacement may improve outcomes in pregnant women with subclinical hypothyroidism (SCH), the extent to which they receive treatment is unknown. Objective: To describe levothyroxine (LT₄) treatment practices for pregnant women with SCH. Design: Retrospective cohort study. Setting: Large US administrative claims database. Participants: Pregnant women with SCH defined by untreated TSH 2.5 to 10 mIU/L. Main Outcome Measure: Initiation of LT₄ as a function of treating clinician specialty (endocrinology, obstetrics/gynecology, primary care, or other), baseline TSH, patient clinical and demographic factors, and US region. Results: We identified 7990 pregnant women with SCH; only 1214 (15.2%) received LT₄. Treatment was more likely in patients with higher TSH, obesity, recurrent pregnancy loss, thyroid disease, and cared for by endocrinologists. Proportion of treated women increased over time; LT₄ treatment was twice as likely in 2014 as in 2010. Women in Northeast and West US were more likely to receive LT₄ compared with other regions. Asian women were more likely, whereas Hispanic women were less likely, to receive LT₄ compared with white women. Endocrinologists started LT₄ at lower TSH thresholds than other specialties, and treated women who were more likely to have had recurrent pregnancy loss and thyroid disease than women treated by other clinicians. Conclusions: We found large variation in the prescription of LT₄ to pregnant women with SCH, although most treatment-eligible women remained untreated. Therapy initiation is associated with geographic, clinician, and patient characteristics. This evidence can inform quality improvement efforts to optimize care for pregnant women with SCH.