Maternal Use of Drugs for Thyroid Disease and Infant Congenital Malformations
Use of thyroxine substitution at hypothyroidism seems not to be associated with any major teratogenic risk—the effects which have been found seem to be explained by concomitant drug use.
Use of propylthiouracil at hyperthyroidism is probably not associated with a major malformation risk. Suggested effects on specific, mainly less severe, malformations are based on low numbers and different studies identified different malformations in excess. Probably propylthiouracil has a low if any teratogenic potential, and it may be the drug of choice in early pregnancy. Methimazole and related drugs are linked to a specific constellation of malformations, notably scalp defects, choanal atresia, esophageal atresia, and omphalocele. The risk for these malformations is much increased, resulting in an about doubling of the risk of any major malformation. If possible, this drug should be avoided in early pregnancy. If it has been used, prenatal diagnosis may at least be able to identify omphalocele early enough to permit an interruption of pregnancy.
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