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AmniocentesisWhat 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 Approximately 2 tablespoons of fluid is withdrawn.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.
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. Click here to link to more information about chromosomes and chromosome abnormalities.
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fluid that is withdrawn during the amniocentesis is sent for AFP testing.
You may know that you are at higher risk of carrying a fetus with a certain
inherited genetic condition. This risk may be known because you have a family
member that has been diagnosed with a genetic condition or you and your partner
have had carrier testing. Depending on your family and medical history,
testing for a specific genetic condition may be available. It is important
to realize that not all genetic conditions can be tested for by amniocentesis
and amniocentesis does not test for all genetic conditions.
What are the limitations of the amniocentesis results? A normal result is great news and reassuring. Unfortunately a normal result does not rule out most birth defects, genetic conditions or mental retardation. What are the risks of amniocentesis? The risk of miscarriage following an amniocentesis is estimated to be less than 1 in 300; recent studies suggest that the risk of miscarriage may be lower. About 1 in 100 women will have uterine cramping, leakage of fluid or bleeding from the vagina following an amniocentesis. Most of them do well and do not have a miscarriage. Infection is very rare following an amniocentesis. What are my options? Your options will depend on how far along you are in your pregnancy. Your options will depend on how far along you are in your pregnancy. If you are in the first trimester (less than 12 weeks), you may choose to have first trimester screening, chorionic villus sampling (CVS), Integrated (first and second trimester) screening, Quad screening (second trimester screening), or amniocentesis. If you are over 13 weeks gestation your options are expanded AFP screening Quad screening, ultrasound evaluation or amniocentesis. You can decide to decline all genetic screening and testing. Click here for more information on prenatal testing options. Who should have Amniocentesis? Women at higher risk of carrying a fetus with a chromosome abnormality, genetic condition or birth defect may wish to consider having an amniocentesis procedure. Women that are very concerned about the risk of having a fetus with a chromosome abnormality may also consider having an amniocentesis. Some of the more common reasons a woman considers an amniocentesis are:
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