Amniocentesis
What is Amniocentesis?Amniocentesis is the withdrawal of a small amount of amniotic fluid (water surrounding the fetus (unborn baby) through a woman's abdomen. Typically, the procedure is performed between 15 to 19 weeks gestation (counting from the first day of the last menstrual period). Amniocentesis tests the fetus for certain genetic conditions and birth defects. The test results are usually available in 2 weeks. Women at higher risk of carrying a fetus with a chromosome abnormality, genetic condition or birth defect may wish to consider having an amniocentesis.
How is amniocentesis performed?
Before the amniocentesis, an ultrasound exam is performed to look at the fetus, uterus, placenta and amniotic fluid. The procedure consists of placing a very thin needle through your abdomen into the amniotic fluid while watching with ultrasound. Approximately 2 tablespoons of fluid is withdrawn. Some women say the procedure does not hurt, while others say they feel pressure or cramping during the procedure.
What tests can be performed on amniotic fluid?
Different tests can be performed on amniotic fluid depending on your family and medical history. It is important to realize that amniocentesis does not test for all genetic conditions or birth defects.
- Testing for chromosome abnormalities
- Testing for birth defects
Amniotic fluid contains cells from the fetus; therefore, it has the same genetic information as the fetus. Amniocentesis detects over 99% of all chromosome abnormalities. Test results are usually available within 2 weeks.
A limited number of birth defects (e.g. open neural tube defects, abdominal wall defects) can be detected by amniocentesis. These birth defects are associated with an increased level of alpha-fetoprotein (AFP) in the amniotic fluid. Ultrasound may also show these birth defects. Some of the amniotic fluid that is withdrawn during the amniocentesis is sent for AFP testing.
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