Prenatal diagnosis of genetic diseases.

The prenatal diagnosis of genetic disorders has become one of the most important tools in medical genetics and has changed the face of genetic counseling. Over 100 inherited metabolic diseases, all chromosomal abnormalities and a number of major congenital malformations can already be diagnosed at relatively early stages of fetal development. Various techniques at different stages of pregnancy are presently available. The earliest procedure, using chorionic villus biopsies, can be performed at approximately 8 weeks of gestation; however, the safety and efficacy of this method are not clear. Amniocentesis is performed at 16 weeks of gestation, and analyses of amniotic fluid and amniocytes are still the most commonly used diagnostic procedures to detect genetic disorders in the fetus. Moreover, real-time ultrasonography and fetoscopy permit the detection of a large number of fetal structural abnormalities in the second trimester of pregnancy through fetal blood samples, fetal skin biopsies, and observation of the fetal external anatomy.