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

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 for you or you’re seeking out knowledge on your own, the information, statistics and myths surrounding this prenatal diagnostic test can feel a bit overwhelming. But the good news is—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 the real breakdown around its risks.

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.

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 fetus. An amnio tests the amniotic fluid, which contains your baby’s genetic material, for chromosome 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 between the two. 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.

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 overall is an extremely personal decision. Some women elect not to pursue any prenatal testing options. For others, however, the information a prenatal test like an amnio can provide can be empowering.

While the choice is ultimately a very 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.
  • A previous pregnancy with a chromosomal or genetic abnormality.

Amniocentesis Procedure

Like any medical procedure, it’s helpful to know what to expect if you’re preparing for an amniocentesis. 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. (But 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. The needle will then be removed.

It’s normal to experience a bit of stinging as the needle enters your skin and some mild cramping as the amniotic 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. (Although you may want to lay low with sex and strenuous activity for a few days.)

Amniocentesis Risks and Complications

Amniocentesis is an invasive test and, as is the case with any invasive medical procedure, it does carry with it some risks—the primary one being miscarriage. But there are many misconceptions around the likelihood of these risks, and knowing the statistics can be a huge reassurance if you’re considering this prenatal test.

According to the American Pregnancy Association, 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 slight, 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.

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.)

Amniocentesis Results and Accuracy

The results of an amnio are usually available in about two weeks. An amnio is a diagnostic test, which means that other than in extremely rare instances, the results are always correct. This is in contrast to a screening test, such as a first trimester screen or a cell-free DNA screening, which tell you if your baby is more likely than others to have a certain condition.

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.

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