Prenatal diagnosis encompasses such procedures as amniocentesis, chorion biopsy, ultrasound, fetoscopy, and analysis of maternal blood.
Amniocentesis is the transabdominal puncture of the uterus and the amniotic sac. A hollow needle is inserted into the amniotic sac under ultrasound, which helps to avoid the placenta. Fluid from the amniotic sac as well as amniotic cells (amniocytes) are withdrawn. The extracted material can be used for analysis of chromosomes with PCR and FISH, diagnosis of inborn errors of metabolism, measurement of alpha-fetoproteins (neural tube defects) and phopholipids (surfactant, evaluation of the maturity of the lungs).
Chorionic villus sampling (CVS) can be performed by means of transcervical puncture of the chorion villi during the embryonic and early fetal periods. During later pregnancy, the puncture also can be performed transabdominally. This biopsy can be carried out between weeks 7-11 of pregnancy. Unlike in amniocentesis, cell cultures are not needed and so the result can be obtained immediately.