Amniocentesis

What is an amniocentesis?

An amniocentesis, also known as an amnio, is a diagnostic test done during pregnancy to check for certain birth defects or chromosomal conditions, such as Down syndrome. Unlike screening tests, which estimate risk, the amniocentesis prenatal test provides definitive results about your baby’s genetic health.

In this outpatient test, your provider will extract a small amount of amniotic fluid containing fetal cells to send to the lab for testing. Amniotic fluid is a clear or light-yellow fluid comprised of fetal urine that surrounds and protects the baby in the uterus. When tested, its cells and other substances can give clues about your baby’s health.

Before having an amniocentesis, you may want to meet with a genetic counselor at The Ohio State University Wexner Medical Center in Columbus, Ohio. These specially trained experts will help you understand what the results might tell you about your baby, as well as how to process that information.

Why is an amniocentesis performed?

Your provider may recommend an amniocentesis to gather precise information about your baby’s health when there’s a higher risk of genetic or chromosomal abnormalities, or when earlier screenings suggest the need for further testing. For this reason, not every woman who is pregnant gets an amniocentesis.

Your provider may recommend the procedure for several reasons, including:

Abnormal prenatal genetic screening results or ultrasound abnormalities that indicate an increased risk for conditions such as Down syndrome or trisomy
Maternal age of 35 or older, when the likelihood of chromosomal abnormalities is higher
Family history of genetic disorders, or if you or your partner is a known carrier of inherited conditions
Previous pregnancy complications, such as a chromosomal abnormality or a birth defect
To diagnose a fetal infection, in specific cases

In all cases, the goal of an amniocentesis is to provide clear, reliable information so you and your care team can make informed decisions about your pregnancy and prepare for the safest possible delivery.

When is amniocentesis performed?

An amniocentesis is done any time after 15 weeks of pregnancy.

What does an amniocentesis test for?

An amniocentesis might be performed to diagnose a condition, explore potential 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.
Fluid drainage: When too much amniotic fluid builds up during pregnancy (a condition called polyhydramnios), an amniocentesis can drain the fluid.
Infection diagnosis: Occasionally, the procedure is performed to diagnose an infection in the baby and the uterus.

What conditions can an amniocentesis detect?

Doctors recommend an amniocentesis to detect a range of genetic, chromosomal and developmental conditions that affect a baby’s health and growth. The most common include:

Chromosomal abnormalities
Neural tube defects, including spina bifida and anencephaly
Inherited genetic disorders, such as cystic fibrosis, Tay-Sachs disease, sickle cell disease and muscular dystrophy
Fetal infections, such as cytomegalovirus (CMV) or toxoplasmosis
Rh incompatibility or anemia

How accurate is an amniocentesis?

Results from an amniocentesis are >99% accurate. The test may tell you if your baby has a certain condition, but it can’t tell how severe the condition is.

What’s the difference between amniocentesis and CVS?

Amniocentesis and chorionic villus sampling (CVS) are both prenatal diagnostic tests that detect genetic and chromosomal conditions. They differ in timing, technique and type of sample collected.

CVS is performed earlier in pregnancy, typically between 10 and 13 weeks, and involves taking a small sample of placental tissue. Amniocentesis is performed after 15 weeks, collecting a small amount of amniotic fluid.

Both tests are highly accurate, but CVS cannot detect certain conditions, such as neural tube defects. Your provider will recommend the most appropriate test based on your stage of pregnancy, risk factors and personal preferences.

Risks of an amniocentesis

An amniocentesis is generally a very safe procedure. However, there are some rare risks, including:

Bleeding or leaking of amniotic fluid from the 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 (between one and three out of 1,000 women experience a miscarriage after the test) this risk should still be considered. If you have a high-risk pregnancy, you and your provider will weigh having the prenatal test knowledge against the risks of an amniocentesis.

How is an amniocentesis performed?

Steps to the procedure include:

While lying down, your belly will be cleaned with an antiseptic.
Using an ultrasound, we check the position of the baby and the placenta before guiding a thin needle into the belly to withdraw a small amount of amniotic fluid. You could feel some cramping during this step. Inserting the needle won’t harm your baby. If the needle gets too close to the baby, we will try another spot.
Your baby’s heart rate is monitored during the procedure.
The fluid is sent to the lab, where we’ll examine the cell parts and other substances to check for abnormalities. Preliminary results are typically available within a few days, with final results being available two to four weeks after the procedure.

Is an amniocentesis painful?

Once the needle is placed in the amniotic fluid, the test itself is relatively painless and takes only a few minutes to complete. You’ll feel a pinch from the initial needle going through the skin and may feel some cramping as the needle enters the uterine muscle.

How long does it take to recover from an amniocentesis?

You can expect to recover from an amniocentesis within a day or two. It’s common to feel mild cramping, pressure or soreness at the needle site for several hours afterward. Your provider will usually recommend resting for 24 hours and avoiding strenuous activity, heavy lifting or sexual intercourse. You can typically resume normal activities the next day.

Contact your provider right away if you experience heavy bleeding, fluid leakage, fever or severe pain.

Results of an amniocentesis

You could receive your first preliminary results in as few as two to three days. However, it typically takes between two to four weeks to complete all the testing. Genetic counselors at the Ohio State Wexner Medical Center are 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.

Does insurance cover amniocentesis?

Most prenatal tests, including amniocentesis, are covered by insurance, but coverage can vary. Your care team or billing department can help you verify your benefits before testing.