Thyroid-stimulating hormone, anti-thyroid antibodies, and pregnancy outcomes.

BACKGROUND: Overt thyroid dysfunction has been associated with adverse obstetric outcomes. However, less is known regarding subclinical hypothyroidism or thyroid autoimmunity and their relationship to pregnancy complications. OBJECTIVE: The purpose of this study was to examine the association between prepregnancy anti-thyroid antibodies and subclinical hypothyroidism and preterm delivery, gestational diabetes mellitus, and preeclampsia. STUDY DESIGN: We conducted a secondary analysis of a prospective cohort of 18- to 40-year-old women with 1-2 previous pregnancy losses (n=1193) who participated in a multicenter randomized, placebo-controlled trial of low-dose aspirin. Prepregnancy levels of thyroid-stimulating hormone, free thyroxine, thyroglobulin antibody, and thyroid peroxidase antibody were measured. Relative risks and 95% confidence intervals were estimated with the use of generalized linear models with adjustment for age and body mass index. RESULTS: Among women with an ongoing pregnancy of >20 weeks estimated gestational age, there was no association between prepregnancy thyroid-stimulating hormone level (>2.5 vs ≤2.5 mIU/L) and preterm delivery (adjusted relative risk, 0.77; 95% confidence interval, 0.40-1.47), gestational diabetes mellitus (adjusted relative risk, 1.28; 95% confidence interval, 0.54-3.04), or preeclampsia (adjusted relative risk, 1.20; 95% confidence interval, 0.71-2.04). Similarly, among women with thyroid antibodies, there was no increase in the likelihood of preterm delivery (relative risk, 1.26; 95% confidence interval, 0.65-2.45), gestational diabetes mellitus (relative risk, 1.33; 95% confidence interval, 0.51-3.49), or preeclampsia (relative risk, 1.02; 95% confidence interval, 0.54-1.92), compared with women without these antibodies. CONCLUSION: Among women with 1-2 previous pregnancy losses, subclinical hypothyroidism and thyroid autoimmunity were not associated with an increased risk of preterm delivery, gestational diabetes mellitus, or preeclampsia. These data support current recommendations that low-risk asymptomatic women should not be screened routinely for thyroid dysfunction or autoimmunity.