Amniocentesis

What is amniocentesis?

Amniocentesis is a prenatal testing procedure usually performed during the second or third trimester of pregnancy. It can diagnose certain chromosomal conditions (such as Down syndrome) or genetic conditions (such as cystic fibrosis). During amniocentesis, your healthcare provider uses a thin needle to remove a small amount of amniotic fluid from the sac surrounding the fetus. This fluid sample then gets tested in a laboratory.

During pregnancy, the fetus grows inside the amniotic sac. Amniotic fluid surrounds and protects the fetus inside the amniotic sac. It also contains some of the fetus's cells. These cells contain genetic information that helps diagnose genetic conditions.

Who gets amniocentesis?

Your healthcare provider may recommend amniocentesis during pregnancy when:

• Ultrasound testing detects a fetal abnormality.
• A prenatal screening test detects an increased risk for a chromosome disorder.
• Certain genetic disorders (such as sickle cell disease or cystic fibrosis) run in your family or you test positive as a carrier of a genetic disorder.
• You’re older than 35 at the time of delivery. This is because individuals over 35 have a higher chance of having a baby with a chromosomal disorder.

What does amniocentesis test for?

An amniocentesis test can detect chromosomal, genetic disorders or congenital disabilities (sometimes called birth defects) such as:

• Down syndrome.
• Tay-Sachs disease.
• Neural tube defects such as spina bifida or anencephaly.

This test can also evaluate:

• Fetal lung development: This is helpful if you need to give birth sooner than expected to protect the health of you or the fetus.
• Rh disease: This is a potentially serious condition where you and the fetus have different blood Rh types.

Amniocentesis is sometimes used to treat polyhydramnios (when you have too much amniotic fluid). Providers use amniocentesis to remove excess fluid.

When is amniocentesis performed?

Most amniocentesis procedures happen between 15 and 20 weeks of gestation (during the second trimester of pregnancy). Having an amniocentesis earlier in pregnancy poses more risks, such as miscarriage.

In some cases, healthcare providers perform amniocentesis tests later in pregnancy. If your provider recommends this test to check fetal lung development or treat polyhydramnios, it will likely happen during the third trimester.

Can I choose not to have amniocentesis?

Yes. If your provider recommends you have an amniocentesis, they will explain why. Your provider (or a genetic counselor) will review the test’s risks and benefits. In the end, whether or not to have this test is up to you.

How should I prepare for an amniocentesis?

Your healthcare provider may provide specific instructions to you for the hours or days leading up to amniocentesis. Generally, there aren’t restrictions on diet or activity. Tell your provider what medications you’re taking so they can let you know if you should stop taking them before your test. Follow any other instructions provided to you.

If you need an amniocentesis test, it’s normal to have questions. Some questions for your provider could include:

• Why do you recommend I have amniocentesis?
• What does amniocentesis mean for the health of the fetus and me?
• What are the potential risks?
• What should I do to prepare for my test?
• When should I expect to get test results?
• Is genetic counseling available to help me?

What are the risks of amniocentesis?

Most amniocentesis procedures are safe. But amniocentesis does present small but serious risks for both you and the fetus.

Some complications of amniocentesis are:

• Cramping.
• Bleeding or leaking amniotic fluid.
• Injury or infection.
• Loss of the pregnancy.
• Premature labor.

Complications from amniocentesis are rare. In less than 1% of cases, amniocentesis leads to miscarriage or early delivery. About 2% of people have spotting or camping after amniocentesis.

Your provider can answer your questions and help you make a decision that’s best for you.

Why is there a risk of miscarriage with amniocentesis?

Miscarriage after amniocentesis is very uncommon. Possible causes could be damage to the amniotic sac or amniotic membranes, losing amniotic fluid, bleeding or infection. Discuss your risk of miscarriage with your healthcare provider before the test.

How do doctors perform amniocentesis?

Your obstetrician or perinatologist performs amniocentesis. First, you’ll lie on your back with your stomach showing. During this procedure, your healthcare provider:

• Cleans a small area on your belly with an antiseptic (to kill germs).
• Applies a special gel on your belly.
• Moves a wand-like device over the gel to capture ultrasound images of the fetus on a nearby monitor.
• Inserts a thin, hollow needle through your abdomen and uterus (into the amniotic sac but away from the fetus).
• Removes a small amount of fluid through the needle.
• Removes the needle from your abdomen.
• Monitors the fetal heartbeat and movement on the ultrasound to ensure they weren’t affected by the procedure.

After the procedure, your healthcare provider sends the amniotic fluid sample to a lab. The lab separates the fetal cells from the amniotic fluid then analyzes the cells. The cells grow for several days in the lab before being tested for genetic conditions or neural tube defects. You should have complete test results in about two weeks.

How long does an amniocentesis take?

An amniocentesis procedure may take around 30 minutes from start to finish. But the actual sampling process (when the needle is inside your uterus) takes only a minute or two.

How painful is amniocentesis?

You may be uncomfortable or feel a sting when your healthcare provider inserts the needle through your skin. You may also have minor menstrual-like cramping during the procedure. Cramps can last for a few hours afterward.

How accurate is an amniocentesis test?

The accuracy of amniocentesis is about 99% in detecting abnormalities. However, it doesn’t measure the severity of the condition.

In some cases, certain factors (such as not collecting enough fluid during the test) may mean the lab can’t analyze the amniotic fluid as expected. This is not common.

Can amniocentesis cause autism?

No, there aren’t any studies that link autism spectrum disorder to amniocentesis.

When will I receive the amniocentesis results?

The time it takes to receive your results will depend on what tests the lab needs to conduct on the amniotic fluid. You may hear some information from your provider as soon as three or four days after your test. Some test results may take two weeks or longer. Genetic counseling may be available to help you understand what the results mean for your pregnancy and what your options are moving forward.

What do the results of an amniocentesis test mean?

If amniocentesis shows that the fetus has a specific health condition, your healthcare provider may refer you to a neonatologist. Remember, amniocentesis doesn’t tell you the severity of the condition, only that a condition is present. Based on the diagnosis, a neonatologist can discuss specific treatments, surgeries, or medications. You may want to discuss what kind of care your baby needs during the first days, months or years of its life.

Can I resume my usual activities after an amniocentesis test?

After an amniocentesis test, you should go home and relax for the rest of the day. You can take acetaminophen for discomfort. Avoid any activity that takes a lot of physical effort, like exercise or sex. You should feel ready to get back to your routine one or two days after the procedure.

When should I call my healthcare provider?

After an amniocentesis, call your provider if you develop:

• Fever.
• Vaginal bleeding.
• Vaginal discharge or leakage of fluid.
• Moderate to severe abdominal pain (anything worse than mild cramps).
• Swelling or redness where your provider inserted the needle.

Is amniocentesis worth the risk?

Only you can determine if amniocentesis is worth the risk. Like most medical procedures, there is a small chance of complications. Your risk of complications depends on several factors. Talk with your healthcare provider about the risk amniocentesis poses to your pregnancy.

Having amniocentesis may help you:

• Determine the best treatment for your child as early as possible.
• Begin planning for a child with special needs.
• Prepare for any lifestyle changes or modifications to your home.
• Identify support groups and resources.

Some people decide against amniocentesis because the test results have no bearing on their decision about the pregnancy, or they don’t want to take any risks in harming the fetus.

What is the cost of an amniocentesis test?

The cost of amniocentesis varies and is dependent on whether or not you have health insurance. Talk to your insurance provider before the test to make sure you understand the out-of-pocket costs and what they are willing to cover. If you don’t have insurance or your plan doesn’t cover amniocentesis, you’ll have to pay for it yourself.

What’s the difference between amniocentesis and chorionic villus sampling?

Chorionic villus sampling (CVS) is another test to diagnose genetic conditions during pregnancy. CVS testing takes a small sample of cells from the placenta (the organ that supplies the fetus with food and oxygen). A CVS is performed earlier in pregnancy, at 10 to 13 weeks. Amniocentesis happens after 15 weeks. Additionally, amniocentesis can test for neural tube defects, but CVS can’t detect these conditions.

Is there a less invasive test available?

Cell-free fetal DNA testing (using the pregnant woman’s blood) can detect some chromosomal abnormalities such as Down syndrome. However, genetic conditions such as cystic fibrosis can’t be diagnosed through this blood test. Amniocentesis is still the gold standard for the diagnosis of chromosomal and genetic disorders.