Amniocentesis, << `am` nee oh sehn TEE sihs, >> is a medical procedure performed during pregnancy to help determine the health and maturity of an unborn baby. It involves the withdrawal and study of a small amount of the amniotic fluid that surrounds the fetus in the mother’s uterus. With this procedure, physicians can accurately diagnose more than 150 serious disorders that may affect the fetus. Such disorders include Down syndrome and Tay-Sachs disease. Amniocentesis involves little risk to either the mother or the fetus.
Amniocentesis is usually performed either late in the fourth month of pregnancy or during the last three months. In the fourth month, its purpose is to detect genetic disorders. The physician can then immediately treat the fetus for certain diseases or plan to treat other disorders right after birth. Some parents choose to end the pregnancy if amniocentesis reveals an incurable disorder. Amniocentesis is performed during the last three months of pregnancy primarily to determine whether the fetus has reached a normal stage of development.
A physician performs amniocentesis with the aid of ultrasound (high frequency sound waves). The ultrasonic waves produce an image of the fetus on a special screen. The physician monitors the position of the fetus while inserting a long hollow needle through the mother’s abdominal wall and into the uterus. The physician then withdraws a small amount of amniotic fluid, which contains cells shed by the fetus. These cells are allowed to grow under controlled laboratory conditions for a few weeks and are then examined. Other procedures used by physicians to determine the health of a fetus are chorionic villus sampling and alpha-fetoprotein analysis (see Genetic counseling ).
