- Objective To investigate pregnancy outcome for patients with treated hyperthyroidism. Methods A population-based study was performed comparing all singleton pregnancies of women with and women without hyperthyroidism at the Soroka University Medical Center, Be'er-Sheva, Israel, between January 1988 and January 2007. Stratified analysis, using a multiple logistic regression model, was performed to control for confounders. Results During the study period, there were 185 636 singleton deliveries in the medical center. Of these, 189 (0.1%) were from women with hyperthyroidism. Using multivariate analysis with backward elimination, the following risk factors were significantly associated with hyperthyroidism: placental abruption; cesarean delivery; and advanced maternal age. No significant differences regarding perinatal outcome were noted between the groups. Women with hyperthyroidism had significantly higher rates of cesarean delivery than did women without hyperthyroidism (20.1% vs 13.1%; P < 0.004), even after controlling for confounders. Conclusions Treated hyperthyroidism was not associated with adverse perinatal outcome. However, hyperthyroidism was found to be an independent risk factor for cesarean delivery.