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Context: Thyroid autoantibody positivity has been associated with an increased rate of obstetrical complications., Objective: We aimed to evaluate the role of thyroid autoantibodies in adverse pregnancy outcomes., Methods: This prospective study was conducted in the Endocrinology Unit of Pisa Hospital. 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. Levothyroxine (LT4) treatment was introduced when TSH was > 2.5 mIU/L in the AT group and when TSH was > 4 mIU/L in the controls. Rates of obstetrical complications in each group were measured., Results: Although the frequency of miscarriage in the 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 2 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 the 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., Conclusion: 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., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)