Amniocentesis

Who Gets the Test?

Your doctor may suggest amniocentesis if you're at a higher risk of some birth defects. Many things can put you at higher risk, such as your age, family history, or an abnormal genetic screening result. You may also need amniocentesis if you have signs of an infection or if you may deliver early. Unlike blood testing, which only shows whether you are at risk, amniocentesis is used to make a diagnosis.

What the Test Does

The doctor takes a sample of the amniotic fluid that surrounds your baby in your womb. Then a lab tests the sample, checking your baby's chromosomes. Those lab tests can include the karyotype test, the FISH test, and microarray analysis.

Testing can help rule out some birth defects, such as Down syndrome, spina bifida, cystic fibrosis, and many others. Doctors also use amniocentesis to check for infections. And, if you're delivering early, amniocentesis can show if your baby's lungs are strong enough to breathe after birth.

Amniocentesis is an invasive procedure. It does pose a small risk of miscarriage or other complications. Talk about the pros and cons with your doctor.

How the Test Is Done

First, the doctor uses ultrasound to locate your baby and pockets of amniotic fluid. Then, the doctor inserts a small needle into your belly to take a sample of amniotic fluid, taking care to keep the needle away from your floating baby. Getting the sample takes about 10 minutes. The test shouldn't hurt, but you will feel some pressure.

What to Know About Test Results

You'll get the results in a few weeks. Amniocentesis is about 99% accurate. If your baby does have a problem, you'll meet with a counselor to talk about your options. Doctors can sometimes treat certain birth defects, such as spina bifida, while your baby is still in the womb. Knowing about an issue can also help by increasing monitoring during the pregnancy and help you and your doctor to prepare.

How Often the Test Is Done During Your Pregnancy

Usually just once, if at all -- at about 15 to 20 weeks. If you have complications or are likely to give birth early, you may need it in your third trimester.

Tests Similar to This One

CVS, karyotype test, FISH test, microarray analysis

WebMD Medical Reference Reviewed by Trina Pagano, MD on May 21, 2016

Sources

SOURCES:

American Academy of Pediatrics healthychildren.org: "Detecting Genetic Abnormalities."

UCSF Medical Center: FAQ: "Amniocentesis."

Ohio State Wexner Medical Center: "Amniocentesis."

Childrens Hospital Boston: "Karyotype, extended banding, fluorescent in situ hybridization (FISH.)"

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