Birth defects after early pregnancy use of antithyroid drugs: A Danish nationwide study

Abstract

Introduction: Hyperthyroidism in pregnant women should be adequately treated to prevent maternal and fetal complications, but teratogenic effects of antithyroid drug (ATD) treatment have beendescribed. Evidence is still lacking in regard to the safetyandchoice ofATDin early pregnancy. Objective: Our objective was to determine to which degree the use of methimazole (MMI)/carbimazole (CMZ) and propylthiouracil (PTU) in early pregnancy is associated with an increased prevalence of birth defects. Methods: ThisDanishnationwideregister-basedcohortstudyincluded817 093childrenlive- bornfrom 1996 to 2008. Exposure groups were assigned according to maternal ATD use in early pregnancy: PTU (n=564);MMI/CMZ(n=1097);MMI/CMZand PTU (shifted in early pregnancy [n=159]); noATD(ATD use, but not in pregnancy [n = 3543]); and nonexposed (never ATD use [n = 811 730]). Multivariate logistic regression was used to estimate adjusted odds ratio (OR) with 95% confidence interval (95% CI) for diagnosis of a birth defect before 2 years of age in exposed versus nonexposed children. Results: The prevalence of birth defects was high in children exposed to ATD in early pregnancy (PTU, 8.0%; MMI/CMZ, 9.1%; MMI/CMZ and PTU, 10.1%; no ATD, 5.4%; nonexposed, 5.7%; P