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Amniocentesis (amniotic fluid test)

What is amniocentesis?

Amniocentesis is a test for pregnant women that looks at a sample of amniotic fluid. Amniotic fluid is a pale, yellow liquid that surrounds and protects an unborn baby throughout pregnancy. The fluid contains cells that provide important information about your unborn baby's health. The information may include whether your baby has a certain birth defect or genetic disorder.

Amniocentesis is a diagnostic test. That means it will tell you whether your baby has a specific health problem. The results are almost always correct. It's different from a screening test. Prenatal screenings tests pose no risk to you or your baby, but they don't provide a definite diagnosis. They can only show if your baby might have a health problem. If your screening tests were not normal, your provider may recommend an amniocentesis or other diagnostic test.

Other names: amniotic fluid analysis

What is it used for?

Amniocentesis is used to diagnose certain health problems in an unborn baby. These include:

  • Genetic disorders, which are often caused by changes (mutations) in certain genes. These include cystic fibrosis and Tay-Sachs disease.
  • Chromosome disorders, a type of genetic disorder caused by extra, missing, or abnormal chromosomes. The most common chromosome disorder in the United States is Down syndrome. This disorder causes intellectual disabilities and various health problems.
  • A neural tube defect, a condition that causes abnormal development of a baby's brain and/or spine

The test may also be used to check your baby's lung development. Checking lung development is important if you are at risk for giving birth early (premature delivery).

Why do I need amniocentesis?

You may want this test if you are at higher risk for having a baby with a health problem. Risk factors include:

  • Your age. Women who are age 35 or older are at higher risk of having a baby with a genetic disorder.
  • Family history of a genetic disorder or birth defect
  • Partner who is a carrier of a genetic disorder
  • Having had a baby with a genetic disorder in a previous pregnancy
  • Rh incompatibility. This condition causes a mother's immune system to attack her baby's red blood cells.

Your provider may also recommend this test if any of your prenatal screening tests were not normal.

What happens during amniocentesis?

The test is usually done between the 15th and 20th week of pregnancy. It is sometimes done later in pregnancy to check the baby's lung development or diagnose certain infections.

During the procedure:

  • You'll lie on your back on an exam table.
  • Your provider may apply a numbing medicine to your abdomen.
  • Your provider will move an ultrasound device over your abdomen. Ultrasound uses sound waves to check the position of your uterus, placenta, and baby.
  • Using the ultrasound images as a guide, your provider will insert a thin needle into your abdomen and withdraw a small amount of amniotic fluid.
  • Once the sample is removed, your provider will use the ultrasound to check your baby's heartbeat.

The procedure usually takes about 15 minutes.

Will I need to do anything to prepare for the test?

Depending on the stage of your pregnancy, you may be asked to keep a full bladder or to empty your bladder right before the procedure. In early pregnancy, a full bladder helps move the uterus into a better position for the test. In later pregnancy, an empty bladder helps make sure the uterus is well positioned for testing.

Are there any risks to the test?

You may have some mild discomfort and/or cramping during and/or after the procedure, but serious complications are rare. The procedure does have a slight risk (less than 1 percent) of causing a miscarriage.

What do the results mean?

If your results were not normal, it may mean your baby has one of the following conditions:

  • A genetic disorder
  • A neural tube birth defect
  • Rh incompatibility
  • Infection
  • Immature lung development

It may help to speak to a genetic counselor before testing and/or after you get your results. A genetic counselor is a specially trained professional in genetics and genetic testing. He or she can help you understand what your results mean.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about amniocentesis?

Amniocentesis isn't for everyone. Before you decide to get tested, think about how you'd feel and what you might do after learning the results. You should discuss your questions and concerns with your partner and your health care provider.

References

  1. ACOG: Women's Healthcare Physicians [Internet]. Washington D.C.: American College of Obstetricians and Gynecologists; c2019. Prenatal Genetic Diagnostic Tests; 2019 Jan [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.acog.org/Patients/FAQs/Prenatal-Genetic-Diagnostic-Tests
  2. ACOG: Women's Healthcare Physicians [Internet]. Washington D.C.: American College of Obstetricians and Gynecologists; c2019. The Rh Factor: How It Can Affect Your Pregnancy; 2018 Feb [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.acog.org/Patients/FAQs/The-Rh-Factor-How-It-Can-Affect-Your-Pregnancy
  3. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2020. Amniotic Fluid Analysis; [updated 2019 Nov 13; cited 2020 Mar 9]; [about 2 screens]. Available from: https://labtestsonline.org/tests/amniotic-fluid-analysis
  4. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2020. Neural Tube Defects; [updated 2019 Oct 28; cited 2020 Mar 9]; [about 2 screens]. Available from: https://labtestsonline.org/conditions/neural-tube-defects
  5. March of Dimes [Internet]. Arlington (VA): March of Dimes; c2020. Amniocentesis; [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.marchofdimes.org/pregnancy/amniocentesis.aspx
  6. March of Dimes [Internet]. Arlington (VA): March of Dimes; c2020. Amniotic Fluid; [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.marchofdimes.org/pregnancy/amniotic-fluid.aspx
  7. March of Dimes [Internet]. Arlington (VA): March of Dimes; c2020. Down Syndrome; [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.marchofdimes.org/complications/down-syndrome.aspx
  8. March of Dimes [Internet]. Arlington (VA): March of Dimes; c2020. Genetic Counseling; [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.marchofdimes.org/pregnancy/genetic-counseling.aspx
  9. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2020. Amniocentesis: Overview; 2019 Mar 8 [cited 2020 Mar 9]; [about 3 screens]. Available from: https://www.mayoclinic.org/tests-procedures/amniocentesis/about/pac-20392914
  10. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Amniocentesis: Overview; [updated 2020 Mar 9; cited 2020 Mar 9]; [about 2 screens]. Available from: https://ufhealth.org/amniocentesis
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2020. Health Encyclopedia: Amniocentesis; [cited 2020 Mar 9]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=92&contentid=p07762
  12. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Amniocentesis: How It Is Done; [updated 2019 May 29; cited 2020 Mar 9]; [about 6 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/amniocentesis/hw1810.html#hw1839
  13. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Amniocentesis: Results; [updated 2019 May 29; cited 2020 Mar 9]; [about 9 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/amniocentesis/hw1810.html#hw1858
  14. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Amniocentesis: Risks; [updated 2019 May 29; cited 2020 Mar 9]; [about 8 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/amniocentesis/hw1810.html#hw1855
  15. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Amniocentesis: Test Overview; [updated 2019 May 29; cited 2020 Mar 9]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/amniocentesis/hw1810.html
  16. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Amniocentesis: Why It Is Done; [updated 2019 May 29; cited 2020 Mar 9]; [about 4 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/amniocentesis/hw1810.html#hw1824

The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.