Thyroid Function Rather Than Thyroid Antibodies Affects Pregnancy and Perinatal Outcomes: Results of a Prospective Study.

Abstract

CONTEXT Thyroid autoantibodies-positivity has been associated with an increased rate of obstetrical complications. OBJECTIVE To evaluate the role of thyroid autoantibodies in adverse pregnancy outcomes. DESIGN This was a prospective study. SETTING The study was conducted in the Endocrinology Unit of Pisa Hospital. PATIENTS A total of 975 pregnant women were studied from 2012 to 2021; 572 (59%) were diagnosed with autoimmune thyroid (AT) diseases; 403 (41%) served as controls. INTERVENTION Levothyroxine (LT(4)) treatment was introduced when TSH was > 2.5 mIU/L in AT group and when TSH was > 4 mIU/L in the controls. MAIN OUTCOME MEASURES Rates of obstetrical complications in each group were measured. RESULTS Although the frequency of miscarriage in AT group was greater (4.8%) than in the controls (2.9%), no significant differences were detected (P = 0.181). There were no differences between the two groups concerning the other pregnancy complications, and no association with the titer of thyroid antibodies was observed. The frequency of congenital malformations was greater in AT group than in the controls (P = 0.019), but no correlation with major congenital malformations was detected (P = 0.872). Given that thyroid hormone concentrations were strictly controlled in our population, we documented a tendency (not significant) toward an increase in miscarriage and preterm birth among women with TSH > 4 mIU/L. CONCLUSIONS If thyroid function is adequately controlled, the presence and titer of thyroid autoantibodies does not negatively influence gestation. Although not significant, suboptimal thyroid hormone status seems to affect pregnancy outcomes more than thyroid autoimmunity.