Amniocentesis Test: Purpose, Risks and Accuracy
Everything You Need to Know About the Amniocentesis Test
March 1, 2019

Everything You Need to Know About the Amniocentesis Test

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Everything You Need to Know About the Amniocentesis Test.
Everything You Need to Know About the Amniocentesis Test

Making the decision to get an amniocentesis can be a big one. Whether your doctor has recommended the test or you’re seeking knowledge on your own, the information, statistics and myths surrounding this prenatal diagnostic test can feel a bit overwhelming. But they don’t have to be.

We’re walking you through the amniocentesis from start to finish: what it is and what it tests for, why you might want one, how it’s performed and what the risks are.

What is Amniocentesis?

Amniocentesis is a prenatal diagnostic test in which a needle is used to take amniotic fluid out of the uterus for testing. The American College of Obstetricians and Gynecologists (ACOG) recommends that “all pregnant people be offered both prenatal screening and prenatal diagnostic testing.”

According to ACOG, “The most common diagnostic test is amniocentesis, followed by chorionic villus sampling (CVS). Many pregnant people may choose to undergo screening initially and proceed to diagnostic testing if there is a positive screening test or abnormalities on ultrasound.”

What is the Purpose of the Amniocentesis Test?

The purpose of the amniocentesis test, also called an amnio, is to provide diagnostic information about the health of a baby. An amnio tests the amniotic fluid, which contains your baby’s genetic material, for chromosomal abnormalities such as Down Syndrome or Turner Syndrome, neural tube defects like spina bifida and genetic disorders such as cystic fibrosis, among many other things. It’s also a way to check your baby’s lung development in instances where premature birth may be imminent.

When is an Amniocentesis Performed?

Amniocentesis is most often performed between 15 weeks pregnant and 20 weeks pregnant. In certain instances, it can also be done later in the third trimester.

Amniocentesis vs. CVS Test

Amniocentesis and chorionic villus sampling (CVS) are both prenatal diagnostic tests, but there are a few major differences. An amnio tests a small sample of amniotic fluid via a needle inserted into the abdomen. CVS, however, tests a small sample of tissue from the placenta and can be performed either through the abdomen or via the vagina using a catheter.

We asked Dr. Carla Williams (MD, FACOG) to compare the risks of a CVS test versus amniocentesis. “The risks are similar,” she says. “[They’re both] an aspiration done with a needle, you can feel pain at the site, you might have some bleeding and there’s risk of rupture of membranes.”

CVS also takes place earlier in pregnancy than an amnio, usually between 10 weeks pregnant and 13 weeks pregnant.

Why is an Amniocentesis Performed?

Prenatal testing is an extremely personal decision, and some parents opt to forego prenatal testing options. For others, however, the information a prenatal test like an amnio can provide can be empowering.

Unlike screening tests, which vary in accuracy, diagnostic tests can offer more reliable information. “Really, it’s a matter of understanding what the screening test is telling you,” says Dr. Williams. “It’s not a diagnosis, it’s that you have a certain risk, and that risk will vary depending on which condition was possibly detected. There are false positives, false negatives. There are no guarantees when it comes to a screening test, and again the risk—how sensitive it is, how specific it is—is going to vary.”

And as always, if you’re unsure about something, talk to your doctor. “If you feel like you should be having a diagnostic test, that’s something your provider should be offering you,” Dr. Williams suggests.

While the choice is a personal one, there are a few risk factors that may lead your healthcare provider to recommend an amniocentesis. They include:

  • A family history of a genetic condition or a partner who is a known carrier.
  • You’re 35 or older.
  • Abnormal prenatal screening results or an abnormal ultrasound.
  • You’ve had a previous pregnancy with a chromosomal or genetic abnormality.

What to expect from an amniocentesis procedure

Like any medical procedure, with an amniocentesis, it’s helpful to know what you’re going into. The good news is an amnio is relatively quick, and most women don’t experience much discomfort.

Your healthcare provider will use an ultrasound and a needle to perform an amniocentesis. You’ll lie on your back on an exam table and will need to remain very still during the procedure. It doesn’t take very long, which makes that part a lot easier. After cleaning your abdomen with an antiseptic, the doctor will use an ultrasound to guide a thin, hollow needle through your abdomen into your uterus and remove a small amount of amniotic fluid, and then remove the needle.

It’s normal to experience a bit of stinging as the needle enters your skin and some mild cramping as the fluid is withdrawn. It’s also common to feel sore afterwards, especially around the area where the needle was inserted. The majority of women don’t experience much pain with an amnio at all. And you’ll be able to resume your normal levels of activity immediately after the procedure, though you may want to lay low with sex and strenuous activity for a few days.

What are the risks and potential complications with amniocentesis?

As is the case with any invasive medical procedure, amniocentesis does come with some risks—the primary one being miscarriage. But there are misconceptions around the likelihood of these risks, and knowing the statistics can be reassuring if you’re considering it.

According to the American Pregnancy Association (APA), the risk of miscarriage from amniocentesis ranges from 1 in 400 to 1 in 200. In facilities where amnios are performed regularly, this rate is closer to 1 in 400—a 0.25% risk. Further, a 2008-2010 study of nearly 150,000 women found that neither CVS nor amnio was associated with an increased risk of miscarriage or stillbirth.

So what does this mean? Statistically speaking, amniocentesis is an extremely safe procedure. The risk of miscarriage is very slim, and in many cases, pregnancy loss following an amnio can be attributed to other pregnancy-related and maternal factors, not from the amnio itself. Risk can be largely mitigated by the skill level of the doctor performing the procedure—so be sure to speak with your provider about their specific miscarriage rates and choose someone with a good deal of experience performing the procedure. Dr. Williams advises speaking to a Maternal Fetal Medicine (MFM) specialist to address your specific concerns, if possible.

After the procedure, “you can feel pain at the site, you might have some bleeding, and there’s risk of rupture of membranes,” says Dr. Williams. Other risks of amnio include infection, cramping or spotting, leaking amniotic fluid, passing an infection (such as HIV) or Rh problems onto your baby. (This is preventable by receiving an injection prior to the amnio if you are Rh negative.)

What can you expect from amniocentesis results?

The results of an amnio are usually available in about two weeks. If the results of your amnio are abnormal, many hospitals have genetic counselors on staff who can help you to understand your results and make the decision that’s right for you and your family. If not, you can locate one via the National Society of Genetic Counselors. Websites like Genetics Home Reference, a division of the National Institute of Health, can also be helpful in researching various genetic conditions.

If you have an amniocentesis, do something nice for yourself after the test and try to relax until you get your results.

This information is provided for educational and entertainment purposes only. We do not accept any responsibility for any liability, loss or risk, personal or otherwise, incurred as a consequence, directly or indirectly, from any information or advice contained here. Babylist may earn compensation from affiliate links in this content. Learn more about how we write Babylist content and the Babylist Health Advisory Board.