Amniocentesis

What To Think About

• Normal results from amniocentesis do not guarantee that your baby will be healthy.
• Amniocentesis in early pregnancy is not done as a general screening test for birth defects because it has some risk to your baby and cannot find some common birth defects. There is a small chance (about 1 in 400) that amniocentesis may cause a miscarriage. Amniocentesis is done when the risk of a birth defect or disease is higher than the risk of the test. Amniocentesis can be done to help you prepare if your baby has a possible birth defect or to help you make a decision about ending the pregnancy if a serious problem is found. For more information about amniocentesis in early pregnancy, see:

  Should I have an amniocentesis?

• In some cases amniocentesis can be done between the 12th and 15th weeks of pregnancy, but there may be a greater risk to your baby. Talk to your doctor about the risks and benefits of an early amniocentesis.
• Amniocentesis cannot be done if the amount of amniotic fluid is very small or if the placenta is in front of your baby.
• Chorionic villus sampling (CVS) is another test that can find many fetal problems. CVS can be done earlier in pregnancy (at about 10 to 12 weeks) than amniocentesis, and results are ready sooner. It can find more than 100 genetic diseases. One study showed that CVS also has about a 1 in 400 chance of miscarriage when it is done by a highly trained provider. CVS cannot be used to find neural tube defects. For more information, see the medical test Chorionic Villus Sampling (CVS).
• Fetoscopy is a new test that allows your doctor to look at your baby using a long, thin tube put through a small cut in your belly. Samples of your baby's blood and tissue also can be collected. Fetoscopy carries a higher chance of miscarriage than amniocentesis and is not widely available. For more information, see the medical test Fetoscopy.
• Amniocentesis has a very small chance of causing bleeding that could lead to mixing your blood and your baby's. Therefore, if you have Rh-negative blood, you will be given a vaccine (RhoGAM) to prevent Rh sensitization which could harm your baby if he or she has Rh-positive blood.
• Amniotic fluid has cells that have been shed by your developing baby. The cells are checked for the number and size of chromosomes (karyotype) to see if there are any problems. For more information, see the medical test Karyotype Test.
• If Rh incompatibility is a concern, amniocentesis may be done several times throughout your pregnancy to check the possible effects of Rh sensitization on your baby.
• If you have abnormal results from amniocentesis, you should ask your doctor or a genetic counsellor for help in making decisions about the problems your baby may have and about continuing the pregnancy. It will also be helpful to understand your possible risks with future pregnancies.

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Author:	Jan Nissl, RN, BS Sydney Youngerman-Cole, RN, BSN, RNC	Last Updated: October 12, 2006
Medical Review:	Renée M. Crichlow, MD - Family Medicine Siobhan M. Dolan, MD, MPH - Reproductive Genetics Liisa Honey, MD, FRCSC - Obstetrics and Gynecology
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