Thyroid dysfunction and autoantibodies in early pregnancy are associated with increased risk of gestational diabetes and adverse birth outcomes

Context: Maternal thyroid dysfunction, especially in early pregnancy, may lead to pregnancy complications and adverse birth outcomes. Few population-based prospective studies have evaluated these effects and results are discrepant. Objective: We examined the association of thyroid function and autoimmunity in early pregnancy with adverse pregnancy and birth outcomes. Setting and Participants: The study used data from the prospective mother-child cohort "Rhea" study in Crete, Greece. A total of 1170 women with singleton pregnancies participated in this analysis. Maternal serum samples in the first trimester of pregnancy were tested for thyroidhormones (TSH, free T₄, and free T₃) and thyroid antibodies (thyroid peroxidase antibody and thyroglobulin antibody). Multivariable log-Poisson regression models were used adjusting for confounders. Main Outcome Measures: Outcomes included gestational diabetes, gestational hypertension/preeclampsia, cesarean section, preterm delivery, low birth weight, and small-for-gestational-age neonates. Results: The combination of high TSH and thyroid autoimmunity in early pregnancy was associated with a 4-fold increased risk for gestational diabetes [relative risk (RR) 4.3, 95% confidence interval (CI) 2.1- 8.9)] and a 3-fold increased risk for low birth weight neonates (RR 3.1,95%CI 1.2- 8.0) after adjustment for several confounders. Women positive for thyroid antibodies without elevated TSH levels in early pregnancy were at high risk for spontaneous preterm delivery (RR 1.7, 95% CI 1.1-2.8), whereas the combined effect of high TSH and positive thyroid antibodies did not show an association with preterm birth. Conclusions: High TSH levels and thyroid autoimmunity in early pregnancy may detrimentally affect pregnancy and birth outcomes.