Association of thyroid function during pregnancy with the risk of preeclampsia and gestational diabetes mellitus.

OBJECTIVE To estimate the association of maternal thyroid dysfunction with the risk of gestational hypertension and diabetes. Whether the association would be affected by gestational age at diagnosis and thyroid autoimmunity was further explored. METHODS A cohort study of 41647 participants was conducted. Thyroid function (i.e., thyroid-stimulating hormone (TSH) and free thyroxine (FT4)) was measured by electrochemiluminescence immunoassay. Thyroid antibody positivity (e.g., thyroperoxidase, thyroglobulin and TSH receptor antibody) was indicated if the values of these antibodies exceeded the upper targets of ther reference range. The relationship between maternal thyroid dysfunction and the risk of preeclampsia (PE) and gestational diabetes mellitus (GDM) was assessed by multivariate logistic regression. RESULTS Isolated hypothyroxinemia (defined as 5th ≤ TSH ≤ 95th percentile, FT4 95th percentile; FT4 < 5th percentile) was related to the risk of severe PE (OR, 2.59, 95% CI: 1.05-6.37). Positive for TSH receptor antibody was associated with a decline risk of GDM (OR, 0.49, 95% CI: 0.35-0.70). A marginally significant association between overt hypothyroidism detected at the first trimester and the risk of GDM was found (OR, 1.60, 95% CI: 1.00-2.83). The association of thyroid dysfunction with the risk of PE and GDM was stronger among pregnant women who were negative for autoantibodies. CONCLUSION Some types of thyroid dysfunction during pregnancy were associated with the risk of PE and GDM. The associations varied by gestational age at diagnosis and thyroid autoantibody status.