Preimplantation diagnosis and other modern methods for prenatal diagnosis.

Prenatal treatment of congenital adrenal hyperplasia (CAH) has long involved prenatal treatment with dexamethasone, administered to the pregnant woman to prevent genital masculinization of an affected female fetus. Although it is unnecessary to treat unaffected or affected males because their genital development would not be disturbed, there has only been incremental progress in determining fetal gender sufficiently each to avoid treating males and unaffected females. Invasive procedures were initially necessary, with first-trimester amniocentesis at 15-20 weeks and then chorionic villus sampling (CVS) at 10-12 weeks gestation. Two approaches now allow personalized treatment of affected female fetuses prior to female genital differentiation. Only preimplantation genetic diagnosis (PGD) is available prior to clinical pregnancy. Recent technological advances have further allowed both single gene diagnosis (e.g., CAH) and aneuploidy detection concomitantly, resulting in far better pregnancy rates than heretofore possible in assisted reproduction technology.