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Amniocentesis (amniotic fluid test)
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Amniocentesis (amniotic fluid test)

Amniocentesis is a diagnostic test performed during pregnancy to identify genetic disorders, birth defects, and other health conditions in an unborn baby.

What is amniocentesis?

Amniocentesis is a test done during pregnancy where a sample of amniotic fluid is taken from your abdomen. It is used to diagnose certain genetic disorders, birth defects, and other conditions in your unborn baby. The test is usually performed between weeks 15 and 20 of pregnancy.

Your baby grows in an amniotic sac inside your uterus, which is filled with amniotic fluid. This clear or pale yellow liquid surrounds and protects your baby, aids in development, and helps maintain the baby's temperature. The fluid contains cells that provide important information about your baby's health.

As a diagnostic test, amniocentesis provides accurate results regarding whether your baby has a specific health problem. This differs from prenatal screening tests, which carry no risks but only indicate if a baby might have a health problem rather than providing a definitive diagnosis.

What is it used for?

Amniocentesis is commonly used to identify:

  • Genetic and chromosomal disorders, including:
    • Down syndrome: Causes delays in physical and mental development.
    • Cystic fibrosis: A disease of the mucus and sweat glands that can lead to breathing and digestive problems.
    • Sickle cell disease: A group of red blood cell disorders that can cause anemia.
    • Tay-Sachs disease: A rare disease that destroys nerve cells and causes mental and physical problems.
  • Neural tube defects: Severe birth defects of the brain and/or spine, such as spina bifida and anencephaly.

The test may also be used to check lung development if there is a risk of premature birth, or to diagnose infections or illnesses in the baby.

Why do I need amniocentesis?

Amniocentesis is a choice, often recommended if you are at a higher risk of having a baby with a health problem. Risk factors include:

  • Being age 35 or older.
  • Receiving abnormal results from a prenatal screening test.
  • A family history of a genetic disorder or neural tube defect.
  • You or your partner are known carriers of a genetic disorder.
  • You or your partner have a child with a genetic disorder or birth defect.

What happens during amniocentesis?

During the procedure:

  • You will lie on your back on an exam table.
  • A provider applies gel to your belly and uses an ultrasound transducer to locate the baby and placenta.
  • After cleaning your belly, the provider inserts a thin needle to withdraw a small amount of amniotic fluid.
  • The baby's heartbeat is checked via ultrasound following the sample collection.
  • The sample is sent to a lab, with results taking from a few days to a few weeks.

The procedure typically takes about 15 minutes. Afterward, you may be advised to avoid exercise or sexual activity for a day or two.

Risks and Preparation

Preparation: In early pregnancy, you may be asked to keep a full bladder to help position the uterus. In later pregnancy, you will need an empty bladder.

Risks: You may experience mild stinging, pressure, or cramping. Potential side effects include mild discomfort, vaginal bleeding, or minor fluid leakage. There is a very slight risk (less than 1 percent) of miscarriage. Contact your provider if you experience severe cramping, fever, or ongoing leakage or bleeding.

What do the results mean?

  • Normal (negative) results: It is very unlikely your baby has the disorder tested, though this does not guarantee the absence of all health problems.
  • Abnormal (positive) results: It is very likely your baby has the disorder tested.

Your provider will explain the results, and you may wish to consult a genetic counselor to better understand the findings.

Frequently Asked Questions

Unlike some other medical procedures, you are generally allowed to eat and drink normally before an amniocentesis. However, you should avoid taking aspirin or other blood-thinning medications for a few days prior to the procedure unless directed by your doctor, as these can increase the risk of bleeding. Always confirm specific preparation instructions with your provider, as protocols can vary slightly by clinic.
Results typically take one to two weeks for chromosomal analysis (like karyotyping) and up to three to four weeks for more detailed genetic testing. A "normal" result means the specific conditions tested for were not detected in the amniotic fluid cells. An "abnormal" result indicates a deviation from the expected genetic or biochemical profile, which may confirm a diagnosis or require further follow-up testing to clarify the findings. It is important to note that a normal result does not rule out all possible birth defects, only those specifically screened for.
Standard amniocentesis usually tests for common chromosomal abnormalities like Down syndrome and specific genetic conditions if requested. If you have a known family history of a rare genetic disorder, you must inform your provider before the procedure so that specific targeted genetic testing can be added to the panel. Without this prior notification, the lab may only perform standard screening, which might miss the specific familial condition.
You should contact your healthcare provider right away if you experience any of the following: vaginal bleeding, fluid leakage from the vagina (which could indicate a rupture of the amniotic sac), uterine contractions or cramping that does not subside with rest, fever, or chills. While mild discomfort or spotting is common, these specific symptoms can signal complications such as infection or premature labor.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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