The effects of gestational transient thyrotoxicosis on the perinatal outcomes: a case-control study.

Purpose: To study the effects of gestational transient thyrotoxicosis (GTT) on pregnancy outcomes.

Methods: This case-control study retrospectively analyzed 7976 women with singleton pregnancies whose thyroid function was measured before 16 weeks of gestation and who delivered at ≥22 weeks of pregnancy. GTT was defined as hyperthyroidism (free thyroxine [FT4] level: ≥95th percentile) in the early pregnancy, which normalized in mid-pregnancy without thyroid-stimulating hormone receptor antibodies.