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What is amniocentesis?
Amniocentesis provides genetic information about the fetus -- as well as information about its health and maturity -- through the removal of a small sample of amniotic fluid. A needle is inserted through the pregnant woman’s abdominal wall, uterine wall and amniotic sac to withdraw fluid which contains cells that have been shed by the fetus. Those cells are then cultured and analyzed. Amniocentesis can be performed during either the second or third trimester, depending on the reason it is being done. Amniocentesis for genetic diagnosis is most commonly performed between 15 and 18 weeks’ gestation.
What does this procedure entail?
For several hours prior to the amniocentesis, the woman should drink plenty of fluids to ensure an adequate volume of amniotic fluid during the procedure. The test does not require a full bladder. An ultrasound prior to the procedure determines the fetal age, position of the fetus, location of the placenta, fetal heartbeat and the number of fetuses. An ultrasound transducer (a device which delivers the ultrasound scan) remains in place to guide the needle and prevent puncturing of the placenta, fetus and umbilical cord.
The woman's abdomen is washed with a sterile solution and sterile drapes are placed over the area. A local anesthetic is not commonly used since this requires an additional needle insertion. Approximately 15 to 30 ml (1 1/2 to 3 tablespoons) of amniotic fluid is withdrawn. Withdrawal of the fluid takes about two minutes, and the body replaces it within about 12 hours of the procedure. Care is taken when extracting this fluid to avoid contamination of the sample with maternal blood, which would invalidate the results.