During pregnancy, the fetus gestates within the uterus, in a special pouch called the amniotic sac. The amniotic sac is filled with amniotic fluid, a colorless fluid in which the fetus floats, suspended and protected inside the mother’s body. Amniotic fluid is made of a combination of water, protein, minerals and hormones, and it acts to both nourish and protect the fetus.
Amniocentesis is a test that analyzes the composition of amniotic fluid and shed fetal cells within the fluid to determine the health of the fetus, and forecast any likely problems with the fetus and the pregnancy overall.
Before performing the test, a woman’s doctor or health care giver will need to determine the position of the fetus using an ultrasound. Once the position of the fetus is determined, the abdomen is washed and disinfected with an antibacterial agent, then an area on the surface of the abdomen is numbed using local anesthesia. After the local anesthesia takes effect, a long, hollow needle is carefully inserted into the abdomen, positioned carefully so that any movement of the fetus will not be touched by the needle. The needle is used to draw off a sample of amniotic fluid, which is then analyzed.
The analysis of amniotic fluid can identify a wide range of problems with either the pregnancy or the developing fetus. These include abnormal bleeding, infections, lack of sufficient amniotic fluid, and chemical or nutritional imbalances. The fluid can also be analyzed to test for a number of genetic, chromosomal, or birth defects and disorders, such as Down’s syndrome, spina bifida (a malformed spine), anencephaly (missing or incomplete brain), as well as many metabolic disorders. Parents can also find out the gender of the developing fetus. As early as 15 weeks of pregnancy, amniocentesis can be used to test for chromosomal or genetic disorders and birth defects. Amniocentesis is a low-risk procedure, but there is a small risk of fetal injury, and even a risk of miscarriage (0.5 percent). As a pregnancy progresses, the risk to the fetus becomes smaller.
After the test, there may be slight soreness at the site where the needle was inserted, and some women notice cramping after the procedure or some mild vaginal bleeding/leakage of fluid, but others will notice no after effects. The procedure is done on an out-patient basis, with patients returning home the same day.
Amniocentesis is usually reserved for women with specific characteristics (e.g., mothers over the age of 35) and is a successful test for ruling out a wide variety of medical problems and determining general fetal health, but patients who are concerned about particular problems – such as likelihood of specific birth defects or genetic disorders that run in their families – should speak with their doctor or a genetic counselor to determine the best way to diagnose and, if necessary, prepare themselves for special care or follow-up medical procedures.
Last updated: 06-Jun-07