Low birth weight and preeclampsia in pregnancies complicated by hyperthyroidism.

Objective: To determine whether control of hyperthyroidism during pregnancy reduces the risk of low birth weight infants and severe preeclampsia.

Methods: Labor, delivery, and postpartum records of 181 hyperthyroid women were reviewed for maternal and fetal outcomes. Subjects were separated into three groups based on their thyroid status: controlled (n = 34), including women who were euthyroid at presentation and delivery; controlled during pregnancy (n = 90), including women who were hyperthyroid at presentation and euthyroid at delivery; and uncontrolled (n = 57), including women who were hyperthyroid at presentation and delivery.

Results: The risk of low birth weight infants was 0.74 (95% confidence interval [CI] 0.18-3.08) among controlled women, 2.36 (95% CI 1.36-4.12) among women who were controlled during pregnancy, and 9.24 (95% CI 5.47-15.6) among women who were uncontrolled during pregnancy compared to the incidence among nonhyperthyroid mothers. The risk of severe preeclampsia was significantly higher (odds ratio 4.74, 95% CI 1.14-19.7) among uncontrolled women compared with those who were controlled during their pregnancies. Elevated TSH-receptor antibody levels were not related to preeclampsia. Maternal thioamide therapy did not adversely affect neonatal outcomes.

Conclusion: Lack of control of hyperthyroidism significantly increases the risk of low birth weight infants and severe preeclampsia.