Amniocentesis and chorionic villus sampling for prenatal diagnosis.

During pregnancy, fetal cells suitable for genetic testing can be obtained from amniotic fluid by amniocentesis (AC), placental tissue by chorionic villus sampling (CVS), or fetal blood. A major disadvantage of second trimester amniocentesis is that the results are available relatively late in pregnancy (after 16 weeks' gestation). Earlier alternatives are chorionic villus sampling (CVS) and early amniocentesis, which can be performed in the first trimester of pregnancy.