Prenatal dexamethasone treatment of fetuses at risk for congenital adrenal hyperplasia: benefits and concerns.

Virilization due to congenital adrenal hyperplasia (CAH) can effectively be prevented or diminished by prenatal dexamethasone given to the mother. This treatment, which should only be considered in families with a previous child with a virilizing form of the disease, has to start already at 6-7 weeks of gestation. Thus, the treatment has to be given 'blindly' to all mothers at risk until the diagnosis of an affected female can be ascertained by analysis of DNA from a chorionic villous biopsy, which cannot be performed until the 10th week. Since CAH is inherited as an autosomal recessive disease and only affected girls benefit from the treatment, seven out of eight fetuses are treated unnecessarily. This makes it especially important to monitor possible side effects. Adverse effects on brain and kidneys have been shown in animals exposed to large doses of dexamethasone during the second trimester. Too few follow-up human studies are reported to date to allow definite conclusions on possible side effects in man. Therefore, treatment should be done within controlled clinical studies.