With amniocentesis, a small amount of amniotic fluid is withdrawn from the amniotic sac surrounding the fetus in the uterus. Chromosome analysis is performed on the fetal cells to provide crucial information about the health of the child.
Who is offered amniocentesis?
- Women who are pregnant and will be 35 or older at delivery.
- Couples who have had a baby or a relative with a chromosome abnormality like Down syndrome, an open spine or skull defect, mental retardation, or other birth defects.
- Couples who are known or possible carriers of an inherited disorder like hemophilia, muscular dystrophy, cystic fibrosis, Tay Sachs, or thalassemia.
- Couples with an increased risk of having a baby with an open spine/open skull, Down syndrome, or other disorders based on pregnancy screening or an ultrasound exam.
- Couples who are concerned about having a baby with a chromosome abnormality.
Is amniocentesis safe?
Amniocentesis has been proven to be a very safe procedure for both mother and baby. The observed number of spontaneous abortions occurring after amniocentesis by an experienced physician is 1 in 300 to 1 in 500.
How is amniocentesis performed?
- An experienced physician performs the amniocentesis using ultrasound to carefully insert a slender needle through the mother’s abdominal wall into the amniotic sac to draw a small amount of amniotic fluid containing fetal cells. Some women feel mild cramping or pressure when the needle enters the uterus and most do not feel pain. Wear clothing over your abdomen which is easy to remove for the exam.
- Your physician will examine the fetus by ultrasound to produce images of the fetus on a monitor. This exam is safe for the fetus. It confirms the dating of your pregnancy, detects some birth defects and identifies most twins. This exam cannot detect all birth defects.
- If the test shows your fetus has a problem, the nature of the problem will be discussed with you. Prenatal diagnosis allows couples to make informed decisions and helps with the management of their pregnancy. Supportive genetic counseling is available. Please discuss any questions you may have with your physician and a counselor.
When is amniocentesis performed?
You and your physician may determine the optimal timing for your testing but is typically performed between 16-20 weeks of pregnancy.
Which tests can be performed?
Specific tests are performed depending on the reasons for testing.
- Chromosome analysis – Chromosomes in the cells of the fetus from the amniotic fluid are counted and analyzed. This prenatal test accurately detects more than 99% of chromosome abnormalities.
- Open spine and/or open skull defects – About 99% of these defects may be detected using ultrasound examination and by testing for alphafetoprotein (AFP) and acetylcholinesterase (AChE), the fetal proteins in the amniotic fluid.
- Inherited genetic disorders – Some couples may be carriers of genetic disorders for which prenatal diagnosis can be performed. Carrier testing and prenatal diagnosis are available for many disorders.
Note – Normal test results do not eliminate the possibility your baby may have birth defects and/or intellectual disability.
How are test results reported?
Most test results will be completed in 10 days. Some special genetic tests take one to three more weeks. Please inform your physician and counselor how to reach you so your tests can be quickly reported.
For information about our other prenatal services, please click here for the Center for Medical Genetics website.