Abstract Context An increased risk of birth defects in children born to mothers with hyperthyroidism has been found, and uncertainties prevail on the role of maternal thyroid function and thyroid autoimmunity. Objective To evaluate the association between maternal thyroid function, thyroid autoantibodies, and birth defects. Methods Retrospective cohort study of 20,399 pregnant women with no known thyroid disease and their children from the Danish National Birth Cohort and the North Denmark Region Pregnancy Cohort (NDRPC). Blood samples from early pregnancy (median week 10) were assessed for maternal thyroid-stimulating hormone (TSH) and free thyroxine (fT4) in both cohorts and for thyroid peroxidase antibodies (TPO-Ab) and thyroglobulin antibodies (Tg-Ab) as well as TSH-receptor antibodies (TRAb) and thyroid stimulating immunoglobulin (TSI) in the NDRPC. Information on birth defects was retrieved from hospital diagnoses. Results Altogether 702 children (3.4%) had birth defects, and maternal median TSH (no birth defects; 1.13 mIU/L, birth defects; 1.19 mIU/L, p = 0.1) and fT4 (no birth defects; 15.5 pmol/L, birth defects; 15.7 pmol/L, p = 0.3) did not differ by outcome of birth defect. The prevalence of birth defects was similar in children born to mothers who were TPO-Ab- or Tg-Ab-positive (4.3%) or -negative (4.0%) (p = 0.6), but higher (9.5%) when the mother was positive for TRAb or TSI (p = 0.003). Conclusions In a large Danish pregnancy cohort, no evidence was found that maternal thyroid function in early pregnancy associated with a risk of birth defects. A possible link with maternal thyroid stimulating antibodies warrants further investigation.
Andersen et al. (Tue,) studied this question.