Amniocentesis

What is amniocentesis?

Amniocentesis is a test that diagnoses certain congenital disorders and genetic conditions in a fetus before birth. During amniocentesis, your healthcare provider uses a thin needle to remove a small amount of amniotic fluid from the amniotic sac. This fluid sample is sent to a lab for testing.

The test usually happens between 15 and 20 weeks of pregnancy (during the second trimester). In some cases, it happens in the third trimester.

Your healthcare provider may recommend amniocentesis when:

• An ultrasound detects signs of a congenital (present at birth) condition 
• A prenatal screening test detects an increased risk for a chromosome disorder
• You test positive as a carrier for a genetic condition

Amniocentesis is completely optional. If your provider recommends you have the test, they’ll explain why. They can also discuss the benefits and risks with you.

What genetic disorders can it detect?

An amniocentesis test can detect:

• Cystic fibrosis
• Down syndrome
• Duchenne muscular dystrophy
• Edwards syndrome
• Klinefelter syndrome
• Neural tube defects, such as spina bifida or anencephaly
• Patau syndrome
• Sickle cell disease
• Spinal muscular atrophy (SMA)
• Tay-Sachs disease
• Turner syndrome

This test can also check:

• Fetal lung development. Substances in amniotic fluid can tell your provider if the lungs are mature enough for early delivery. You may need an early delivery if you have pregnancy complications.
• Rh incompatibility. Amniocentesis can tell your provider how severe Rh incompatibility is.

Amniocentesis is also a treatment for polyhydramnios (when you have too much amniotic fluid). Providers use it to remove some of the excess amniotic fluid.

How does amniocentesis work?

Amniocentesis can tell your pregnancy care provider if your baby will be born with a congenital or genetic disorder. Amniotic fluid contains some of the fetus’s cells. These cells contain genetic material that providers can test for certain conditions. During amniocentesis, your healthcare provider inserts a thin needle through your belly and into your uterus to get the fluid. 

How should I prepare for the test?

There usually isn’t anything special you have to do to prepare. Tell your provider what medications you’re taking so they can let you know if you should stop taking them.

It’s normal to have questions about the test. Some questions for your provider could include:

• Why do you recommend I have amniocentesis?
• What are the potential risks?
• What can I expect while I’m having the test?
• When should I expect to get test results?
• Is genetic counseling available to help me?

What should I expect during the test?

A perinatologist usually performs amniocentesis. First, you’ll lie back on an exam table with your belly showing. Then, they’ll:

1. Clean a small area of your belly with an antiseptic (to kill germs).
2. Put a special gel on your belly.
3. Move a wand-like device over the gel to take images of the fetus on a nearby monitor.
4. Insert a thin, hollow needle through your belly and uterus (into the amniotic sac but away from the fetus).
5. Remove a small amount of fluid through the needle.
6. Remove the needle from your belly.
7. Monitor the fetal heartbeat and movement on the ultrasound.

After the procedure, your healthcare provider sends the sample to a lab. The lab separates the fetal cells from the amniotic fluid. The cells grow for several days in the lab. Then, they test the cells for genetic conditions or neural tube defects.

How long does it take?

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

Does it hurt?

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

What are the risks of the test?

Amniocentesis is safe, but there are some risks. Some possible complications are:

• Severe cramping
• Bleeding or leaking amniotic fluid
• Injury or infection
• Preterm labor
• Miscarriage

Complications from amniocentesis are rare. About 1 or 2 in 100 women have spotting or cramping after amniocentesis. In about 1 in 1,000 cases, amniocentesis leads to miscarriage. Talk to your pregnancy care provider about the risks and benefits of the test.

How accurate is amniocentesis?

It’s about 99% accurate. But it can’t tell you how severe the condition is, only that the fetus has the condition.

What should I expect after amniocentesis?

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

When will I get my results?

The time it takes to receive your results will depend on what conditions they’re testing for. You may hear from your provider as soon as three or four days after your test. Some test results may take two weeks or longer.

What do the results mean?

If your results are normal, it means there weren’t any signs of the conditions the test looked for.

If amniocentesis shows that the fetus has a condition, your healthcare provider can explain what that means. Genetic counseling may be available to help you understand what your options are moving forward and what you can expect.

You may also see a neonatologist. They can discuss specific treatments, surgeries or medications you may need. They can also talk about what kind of care your baby needs during the first days, months or years of life.

When should I call my healthcare provider?

After an amniocentesis, call your provider if you have:

• Fever or chills
• Vaginal bleeding (anything more than light spotting)
• Vaginal discharge or leaking fluid
• Moderate to severe abdominal pain (anything worse than mild cramps)
• Swelling or redness where your provider inserted the needle