The prevalence of maternal hyperthyroidism due to Graves’ disease in pregnancy varies from 0.1% to 2.7%. The prevalence of subsequent, transient neonatal Graves’ disease is uncertain, varying from 1.5% to 20% in some studies.

Foetal thyroid development is in progress by week 7 gestation, thyroid hormone synthesis begins in weeks 10-12 and the thyroid is functionally mature by week 25. The causal antibodies in Graves’ disease, thyroid stimulating hormone (TSH) receptor antibodies (TRAb) freely cross the placenta, particularly in the second half of pregnancy thus putting the developing foetus at risk of hyperthyroidism.

Infants with hyperthyroidism may present in utero, usually in the 3rd trimester with signs that include tachycardia, heart failure with non-immune hydrops, IUGR, preterm birth and craniosynostosis.