From Encyclopedia of Sex and Sexuality
A developing baby floats in the uterus within a sac filled with a salty amniotic fluid. At sixteen to eighteen weeks of pregnancy a small amount of this fluid can be removed by inserting a needle through the abdominal wall and into the amniotic sac. (To avoid damage to the fetus, a sonogram is employed, by means of which sound beams penetrate the uterine wall and outline the fetus, placenta, and amniotic fluid.) This procedure is called amniocentesis. Amniocentesis has certain risks to the woman, the pregnancy, and the baby. The risk of interrupting a pregnancy when amniocentesis is used is 1 in 200.
Fluid removed by the needle can be analyzed for certain chemical compounds, enzymes, chromosomes, etc., to help in the prebirth diagnosis of such conditions as mongolism, Tay-Sachs disease in Western European Jews, sickle cell anemia in blacks, B thalassemia in Greeks and Italians, A thalassemia in Southeast Asians, neural tube defects (openings in the spinal column and cranium) that result in such conditions as spina bifida and anencephaly, cystic fibrosis, hemophilia, polycystic kidney disease, and muscular dystrophy. This is just a partial list of the diseases and conditions that the medical profession can now detect in the unborn child.
Amniocentesis is most commonly performed when the mother will be over age thirty-five when her child is born. It must be noted that this is an arbitrary age, and parents may opt for this procedure at any age. Certainly, all women who have already had a chromosomal-defective child should be tested by amniocentesis, as they should if there is a parental chromosome abnormality. Before the advent of amniocentesis, these abnormalities were only detected after the baby’s birth; now these can be detected at a much earlier stage. If gross defects in the fetus are detected, an abortion is usually recommended and performed, although some parents will choose to bring the pregnancy to term and raise the child.