Subclinical Hypothyroidism and Thyroid Autoimmunity Are Not Associated With Fecundity, Pregnancy Loss, or Live Birth

Context: Prior studies examining associations between subclinical hypothyroidism and antithyroid antibodies with early pregnancy loss and live birth suggest mixed results and time to pregnancy (TTP) has not been studied in this patient population. Objective: This study sought to examine associations of prepregnancy TSH concentrations and thyroid autoimmunity with TTP, pregnancy loss, and live birth among women with proven fecundity and a history of pregnancy loss. Design and Setting: This was a prospective cohort study from a large, randomized controlled trial that took place at four medical centers in the United States. Patients or Other Participants: Healthy women, ages 18-40 y, who were actively attempting to conceive and had one or two prior pregnancy losses and no history of infertility were eligible for the study. Intervention: There were no interventions. Main Outcome Measure: TTP, pregnancy loss, and live birth. Results: Women with TSH >= 2.5 mIU/L did not have an increased risk of pregnancy loss (risk ratio, 1.07; 95% confidence interval [CI], 0.81-1.41) or a decrease in live birth rate (risk ratio, 0.97; 95% CI, 0.88-1.07) or TTP (fecundability odds ratio, 1.09; 95% CI, 0.90-1.31) compared with women with TSH <2.5 mIU/L after adjustment for age and body mass index. Similar findings were observed for women with thyroid autoimmunity and after additional adjustment for treatment assignment. Conclusions: Among healthy fecund women with a history pregnancy loss, TSH levels >= 2.5 mIU/L or the presence of antithyroid antibodies were not associated with fecundity, pregnancy loss, or live birth. Thus, women with subclinical hypothyroidism or thyroid autoimmunity can be reassured that their chances of conceiving and achieving a live birth are likely unaffected by marginal thyroid dysfunction.