An amniocentesis, also known as an amnio, is a test done during pregnancy to diagnose certain birth defects or chromosomal conditions, such as Down syndrome.
During the outpatient test, a small amount of amniotic fluid — a clear or light-yellow fluid that surrounds the baby in the uterus and protects it — is extracted from the mother and then sent to the lab for testing. Amniotic fluid has cells and other substances that can give clues about the baby’s health.
While the prenatal test can offer an important glimpse into your baby’s well-being, women with high-risk pregnancies, along with their physicians, must weigh having that knowledge against the risks of an amniocentesis — and be prepared for the results it may provide.
Why is an amniocentesis performed?
Not every woman who is pregnant will experience an amniocentesis.
Generally done between 15 and 20 weeks of pregnancy, an amnio might be recommended by your doctor if you’re older than 35, have a family history of genetic disorders or your first-trimester screenings flagged that your baby might have an increased risk of birth defects.
An amniocentesis might be performed to diagnose a condition, explore issues or treat a problem. These reasons include:
- Genetic testing – An amniocentesis can diagnose chromosomal disorders, like Down syndrome or genetic diseases carried by parents, such as cystic fibrosis. It can also look at neural tube defects.
- Lung maturity – The test, when done later in pregnancy, allows experts to look at amniotic fluid to determine if a baby’s lungs are mature enough for birth.
- Fluid drainage – When too much amniotic fluid builds up during pregnancy — a condition called polyhydramnios — it might be drained through this procedure.
- Infection diagnosis – Occasionally, the procedure is done to diagnose an infection in the baby as well as the mother’s uterus.
Risks of an amniocentesis
There are risks associated with an amniocentesis to consider when choosing whether to have the test or not, including:
- Bleeding or leaking of amniotic fluid from needle-puncture site or the vagina
- Infection of the uterus
- Preterm labor
- Miscarriage
While it’s very rare for an amniocentesis to cause a miscarriage — only about 3 out of 1,000 women experience a miscarriage after the test — this risk should still be considered.
What to expect when having an amniocentesis
Before having an amniocentesis, you may want to talk with a genetic counselor at The Ohio State University Wexner Medical Center. Here in Columbus, Ohio, we have special training to help you understand what the results might tell you about your baby as well as how to handle that information.
The test itself is relatively painless and takes only about 15 minutes.
Laying down, your belly will be cleaned with an antiseptic and then you’ll be administered a numbing agent via an injection. You might feel a sting. Using an ultrasound, we check the position of the baby and the placenta and guide a thin needle into the belly to withdraw 2 tablespoons of amniotic fluid. You could feel some cramping during this step.
Inserting the needle will not harm the baby. If the needle gets too close to the baby, we will try another spot. The baby’s heart rate, blood pressure and other vitals are monitored the entire time. Finally, the fluid goes to the lab where we’ll look at the cell parts and other substances to check for abnormalities.
Results of an amniocentesis
You could receive your results in as few as three to four days; however, it could take up to two weeks.
Genetic counseling may be made available to help you understand the results and your options moving forward.
Depending on the results, our Maternal Fetal Medicine experts will continue to monitor your pregnancy closely and discuss any surgeries, treatments or medicines available.
Our Services
Small pieces of genetic material (DNA) from the pregnancy are in a mother’s blood and are tested to check if a baby is at higher risk for Down syndrome and other genetic chromosomal conditions. This is a screening test and does not give a definite answer. Further testing may be done if cell‐free DNA screening indicates a pregnancy is at high risk.
This ultrasound is provided in partnership with Nationwide Children’s Hospital. It’s performed here are Ohio State and read by a pediatric cardiologist. If a heart defect is found, the pediatric cardiologist will determine its significance and whether the defect will affect your baby prior to birth, will require immediate transfer after birth to Nationwide Children’s or will require heart surgery after birth.
During this test, you’ll count how long it takes your baby to make eight to 10 movements – a kick, flutter, burp, included – in the third trimester. Generally, this should take about an hour. If your baby isn’t moving this much, it might be worth further testing.
You’ll be screened for this during the 36thor 37th week of pregnancy. This test involves swabbing the vagina and rectum and if you test positive, you’ll receive IV antibiotics during labor to prevent infection for the baby.
An abnormal finding during the first trimester can help detect chromosomal abnormalities, heart defects and other genetic syndromes.
Administered during 15 and 22 weeks of pregnancy, this will screen for conditions such as spina bifida, anencephaly, abdominal wall defects and chromosome changes. If results indicate a high risk of these disorders further tests will be performed.