Hyperthyroidism complicating pregnancy: results of treatment by antithyroid drugs in 77 pregnancies.

Seventy-seven pregnancies (79 infants) complicated by hyperthyroidism were seen at three Dublin Maternity Hospitals during a 25 year period. Hyperthyroidism was diagnosed following conception in 14 pregnancies. Treatment was with carbimazole alone in 73 pregnancies, in a usual dose of 5 to 10 mg daily. The total fetal loss was 15.2 per cent with a perinatal loss of 5.1 per cent. The perinatal loss in patients treated with carbimazole alone was 4.1 per cent (excluding one death due to congenital malformation). Four infants (5.1 per cent) had goitre and 57 (85.1 per cent) of the surviving infants were above the 25th centile for gestational age. Spontaneous premature labour occurred in 7 pregnancies (9.1 per cent). There was a relative excess of infants with a birth weight less than the 25th centile, of neonatal goitre and premature labour after pregnancy in which treatment was started following conception. Hyperthyroidism complicating pregnancy can be treated effectively with antithyroid drugs given alone and in the minimal effective dose.