A technique for testing the genetic health of a fetus by inserting a needle through the mother's abdominal wall into the uterus and extracting a small amount of the amniotic fluid, the fluid that surrounds the fetus. Sloughed-off fetal cells (fibroblasts) found in this fluid are then cultured and their DNA examined for defects. This procedure is done in the second trimester, and because of the time needed to do the culture, results aren't generally available until after the 20th week of pregnancy.