Amniocentesis: Prenatal Genetic Testing
Amniocentesis can detect chromosome and genetic problems, including Down syndrome, as well as neural tube defects such as spina bifida.
Amniocentesis (amnio) is a prenatal test. It is used to diagnose certain health problems and birth defects, some of which are genetic, meaning they may be passed down to an unborn baby from his or her parents. If you’re at risk of having a baby with a birth defect, your doctor may recommend you get this test.
What are some reasons for having the test?
You may want to have an amnio if you have any of the following risks:
- You are 35 or older. The older you are, the higher your risk of having a baby with birth defects, such as Down syndrome.
- You have a child or previous pregnancy with a birth defect. Your doctor should offer you testing if you fall into one of these categories.
- Your screening test results were abnormal. A screening test is typically a blood test. It shows if you or your baby is likely to have a certain health condition. If abnormal results come back from the test, your provider should offer you an amnio.
- You have a family history of a genetic condition. You may want to have an amnio if you, the baby’s father or a member of your family has a genetic condition. These include cystic fibrosis, Tay-Sachs disease, spina bifida or sickle cell disease.
What happens during the test?
Your doctor first locates your baby with an ultrasound. Then he or she places a thin needle through your abdomen and uterus into the amniotic sac without hitting the baby. He or she uses the needle to take out a small amount of the cells and fluid that are around the baby in the sac.
The fluid is tested to measure the baby’s protein levels, among other qualities of the fluid. These levels might indicate certain birth defects. Test results can take up to three weeks.
What are the risks involved?
The test is not recommended during early pregnancy because it increases the risk for miscarriage. It’s best to have an amnio in the second trimester between 15 and 20 weeks of pregnancy when there is more amniotic fluid to examine. A third-trimester amnio can confirm a suspected infection in your uterus, for example. If you are at risk of a preterm birth, it can tell whether your baby’s lungs are ready without poking the baby with the needle.
An amnio is painless for some women. Others feel cramping or pressure during the procedure. One to 2 percent have cramping, spotting or leak amniotic fluid after the test. Serious complications from the test are rare. Still, the test does involve a less than 1 percent risk of miscarriage.
What happens after the test?
Usually, results show a healthy baby. If the test does detect a birth defect, talk about your options with your doctor and others providing prenatal care. There may be medications or surgery available for the baby, before or after birth. Amnio results give you knowledge and time to prepare for your baby’s birth and the care he or she will need.
Can I refuse the test?
An amnio test is a personal decision. Talking with genetic counselors, your family, your health care provider and spiritual leaders can help you decide what you want to do. You can also ask about other test options.
By Mary Small, Contributing Writer
For more information, please visit Optum's Health Library
American College of Obstetricians and Gynecologists. Genetic disorders. Accessed: July 13, 2016.
Centers for Disease Control and Prevention. Birth defects: Diagnosis. Accessed: July 13, 2016.
Womenshealth.gov. Pregnancy. Prenatal care and tests. Accessed: July 13, 2016.
March of Dimes. Prenatal care. Amniocentesis. Accessed: July 13, 2016.
Last Updated: July 13, 2016
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