The possibility of prenatal diagnosis of CAH by steroid determinations and HLA typing in amniotic fluid and the knowledge that Dexamethasone (Dexa) crosses the placental barrier induced attempts on prenatal treatment of CAH girls by giving the mothers Dexa during pregnancy. The question is when to start treatment. Androgens start to act at week 8 of gestation, but it is still under discussion whether the fetal adrenals are under hypophyseal control before week 20.We treated the mother of a severely virilized CAH girl during her second pregnancy. We gave Dexa (0.5 mg/d) from week 12 to week 15, stopped for 7 days before amniocentesis, and then continued treatment until delivery. The fetus was diagnosed to be female and homozygous for CAH. Pregnancy and delivery were uncomplicated. The treated girl was virilized to the same degree as her untreated sister; however,clitoromegaly was markedly less developed (2cm in length vs 4cm in the untreated child). Adrenal steroids were elevated slightly in umbilical vein and artery, but highly in plasma at day 5 of life.We see three possible explanations for the fact that virilization was influenced not qualitatively but only quantitatively by prenatal treatment:1. the dose of Dexa may have been too low;2. treatment may have started too late;3. the activity of the fetal adrenals possibly is not influenced by Dexa at the time when early steps of virilization take place.
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