What is an amniocentesis test?
Amniocentesis is a prenatal testing procedure usually performed during the second or third trimester of pregnancy. During amniocentesis, your provider uses a thin needle to remove a small amount of amniotic fluid from the sac surrounding your unborn baby.
This fluid sample then gets tested in a laboratory. Amniocentesis can diagnose certain genetic conditions (such as Down syndrome). It also flags other potential issues that could affect your baby’s health.
What is amniotic fluid?
During pregnancy, an unborn baby grows and develops inside the amniotic sac. Some people call the amniotic sac the “bag of waters.” Amniotic fluid surrounds and protects your baby inside the amniotic sac.
Amniotic fluid looks a lot like water. This fluid also contains some of your baby’s cells. Babies shed these cells as they grow. These cells provide genetic information and other details that can offer clues about your baby’s health before birth.
Who gets an amniocentesis test?
Your provider may recommend amniocentesis during pregnancy when:
- Ultrasound testing detects a fetal abnormality.
- A prenatal screening test detects an increased risk for a chromosome abnormality.
- Certain genetic disorders (such as sickle cell disease or cystic fibrosis) run in your family.
- Moms-to-be are 35 or older at the time of delivery. A mother of higher age increases the overall risk your baby could have a genetic disorder.
What can an amniocentesis test detect?
An amniocentesis test can detect:
- Genetic disorders, such as Down syndrome or Tay-Sachs disease.
- Birth differences (sometimes called birth defects), such as spina bifida.
This test can also evaluate:
- Your baby’s lung development, should you need to give birth sooner than expected to protect the health of you or your baby.
- Other health concerns, such as Rh disease, a potentially serious condition where you and your baby have different blood types.
In some cases, an amniocentesis acts as a treatment, such as for polyhydramnios. Providers may perform this procedure to remove extra amniotic fluid. Having too much amniotic fluid may affect your baby’s growth.
When is amniocentesis performed?
Most amniocentesis procedures happen between 15 and 20 weeks gestation (during the second trimester of pregnancy). Having an amniocentesis earlier in pregnancy poses more risks, such as miscarriage.
In some cases, providers perform amniocentesis tests later in pregnancy. If your provider recommends this test to check your baby’s lung development or treat polyhydramnios, it will likely happen during the third trimester.
Can I choose not to have an amniocentesis?
Yes. If your provider recommends you have an amniocentesis, they will explain why. Your provider (or a genetic counselor) will go over the test’s potential benefits and risks. In the end, whether or not to have this test is up to you.
How should I prepare for an amniocentesis?
Follow any instructions your healthcare provider gives you. Make sure your healthcare provider has an accurate and full list of medications you take and any allergies you have.
Your healthcare provider may ask whether your blood type is Rh negative or positive. If needed, your provider will take steps to safeguard against potential issues that can happen when you have a different blood type than your baby.
Your healthcare provider may instruct you to drink a lot of water or go to the bathroom right before your test. Depending on when you have your test, a full or empty bladder can make it easier for providers to safely perform this test.
How is an amniocentesis procedure performed?
For an amniocentesis, you 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 your baby 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 your baby’s 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 for analysis in a laboratory.
How long does an amniocentesis take?
An amniocentesis procedure may take around 20 minutes from start to finish. But the actual sampling process (when the needle is inside your uterus) takes only a minute or two.
Is an amniocentesis painful?
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 after the procedure.
How accurate is an amniocentesis?
The accuracy of amniocentesis approaches 100%. 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.
Risks / Benefits
Does amniocentesis have risks?
Most amniocentesis procedures are performed safely. But amniocentesis does present small but serious risks for both you and your baby.
In less than 1% of cases, amniocentesis leads to miscarriage (loss of pregnancy) or early delivery. Other risks include an injury or infection that could affect the health of you or your baby. These complications rarely happen.
Your provider can answer questions you have and help you make a decision that’s best for you and your baby.
Recovery and Outlook
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. Avoid any activity that takes a lot of physical effort, such as exercise or sex. You should feel ready to get back to your regular routine one or two days after the procedure.
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 two or three days after your test. Some test results may take two weeks or longer.
You can expect a phone call from a genetic counselor. This trained professional will review your results and help you understand what they mean for you and your baby.
When to Call the Doctor
When should I call my healthcare provider?
After an amniocentesis, call your doctor if you develop:
- Vaginal bleeding.
- Vaginal discharge or leakage of fluid.
- Moderate to severe abdominal pain (anything worse than mild cramps).
What should I ask my healthcare provider?
If you need an amniocentesis test, you may want to ask your provider:
- Why do you recommend I have amniocentesis?
- What does amniocentesis mean for the health of my baby and I?
- What are the potential risks?
- What should I do to prepare for my test?
- When should I expect to get test results?
Healthcare providers perform amniocentesis tests for different reasons. Providers typically recommend amniocentesis when they believe the potential benefits of testing outweigh the small but real risks to you and your baby. This test can provide valuable information about your baby’s health. But you get to make the final decision on whether having an amniocentesis test is right for you and your baby. There is no wrong answer.