We investigated whether thyroid autoantibody status influences pregnancy outcomes in euthyroid women, by comparing abnormal pregnancy outcome rates between those who tested positive for thyroid autoantibodies (Ab+) and those who tested autoantibody-negative (Ab-). Euthyroid pregnant women (n=7,641) underwent tests for serum thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb). The subjects were divided into 4 groups according to thyroid antibody status: TPOAb-/TgAb- (92.9%); TPOAb+/TgAb- (3.2%); TPOAb-/TgAb+ (2.0%); and TPOAb+/TgAb+ (1.9%). The incidence rates of the following abnormal pregnancy outcomes were compared among the 4 groups and analyzed by Fisher's exact test: gestational diabetes, gestational hypertension, placenta previa, placental abruption, premature rupture of fetal membrane (PROM), intrauterine growth restriction, fetal distress, fetal anomalies, stillbirth, preterm birth, and low birth weight. Among the 4 groups, there were no significant differences in age, gestational age, or in the incidence rates of abnormal pregnancy outcomes, except for PROM and low birth weight. The highest incidence rates for PROM and low birth weight were in the TPOAb-/TgAb+ and TPOAb+/TgAb+ subjects, respectively. TgAb positivity and TPOAb positivity were associated with PROM and low birth weight, respectively. Underlying factors that govern the association between thyroid autoantibodies and PROM and low birth weight require further investigation.