• Also Known As:
  • Amniotic Fluid Test
  • Amniotic Fluid Analysis
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Amniocentesis is the removal of a small amount of fluid from the sac that surrounds the baby during pregnancy. This fluid is known as amniotic fluid.

Amniocentesis is usually performed as a diagnostic test in which the amniotic fluid is removed and sent to a lab where it can be analyzed to evaluate the health and development of the fetus.

About the Test

Purpose of the test

There are two main uses of amniocentesis: diagnostic testing of fetal health and removing excess amniotic fluid.

Diagnosis is a way of detecting if a fetus has certain types of developmental abnormalities or health problems. These include but are not limited to:

  • Possible birth defects involving the brain or spinal cord
  • Chromosomal abnormalities such as Down Syndrome
  • Genetic disorders such as cystic fibrosis
  • Abnormal lung development
  • Fetal infection with a virus or bacteria

The second function of amniocentesis is to remove excess amniotic fluid as a therapeutic procedure. In this case, fluid is not removed for testing, and the technical name for this version of the procedure is amnioreduction.

What does the test measure?

An amniocentesis test analyzes a small sample of amniotic fluid. Different kinds of laboratory analyses may be performed depending on the specific purpose of the test.

Amniocentesis can be used to detect whether a fetus has chromosomal changes associated with conditions such as Down Syndrome. These prenatal genetic studies are the most common reason why amniocentesis is performed.

In many cases, amniocentesis also involves measuring alpha fetoprotein (AFP) and acetylcholinesterase (AChE) levels in the amniotic fluid.

AFP is a protein that is normally made by the fetus, but abnormal levels can be related to certain birth defects. AChE is an enzyme that is produced within the fetal spinal cord and brain. It is not normally detected in amniotic fluid. When it is, it may be related to an open neural tube defect, such as spina bifida.

While these are the most common tests performed after amniocentesis, other testing may be ordered to check for bacterial or viral infections or evaluate other aspects of an unborn baby’s health.

When should I have an amniocentesis performed?

Diagnostic amniocentesis is most frequently performed between the 15th and 18th week of pregnancy. It is recommended that amniocentesis be offered to all women interested in diagnostic testing, regardless of age or additional risk factors. However, It is most often performed based on the increased chance of a chromosomal abnormality either due to a mother’s age or an abnormal result from a prenatal screening test.

Prenatal screening generally involves ultrasound and/or blood tests that can detect signs of a potential problem with a baby’s health or development. When there is an abnormal finding on a prenatal screening test, the mother may be offered amniocentesis to help diagnose the cause.

Other situations in which an amniocentesis may be performed due to increased risk include:

  • Having a previous child with a genetic or chromosomal abnormality
  • Having a previous child with certain birth defects
  • When both parents are known carriers of a genetic disorder

Finding an Amniocentesis Test

How to get tested

This procedure has to be ordered by a doctor and performed by an experienced health care provider, such as a perinatologist (maternal-fetal medicine specialist) or an obstetrician/gynecologist (OB-GYN). The procedure can take place in a hospital setting or in an outpatient facility such as a doctor’s office.

Amniocentesis is not typically performed before the first 15 weeks of pregnancy due to the increased risk of being unable to obtain a sufficient sample and an increased risk for complications.

Can I take the test at home?

Amniocentesis cannot be performed at home. It has to be done by a trained medical professional in a hospital or other outpatient care facility.

How much does the test cost?

The price of amniocentesis varies based on where you get the test done and whether you have health insurance. The cost of the test may increase if you have other tests being done along with an amniocentesis.

If you want to know more about the cost of the procedure and how much your insurance covers, you can ask your doctor for an estimate. If you do not have insurance coverage, you can ask a hospital administrato about any available financial assistance programs for the uninsured

Taking an Amniocentesis Test

The sample that is required for a diagnostic amniocentesis is a small amount of amniotic fluid. The fluid is extracted by a long, thin needle that is inserted through the abdomen into the area around the fetus. Once the sample is obtained, it is sent to the lab where detailed testing can be conducted.

Before the test

Depending how many weeks you are into your pregnancy, you might be asked to either urinate or refrain from urinating before the test. At the beginning of pregnancy, a full bladder can help properly position the uterus, but an empty bladder is usually preferred later in pregnancy.

During the test

For this test, you will be asked to lie flat on an exam table. An ultrasound is used to visualize the location of the fetus, placenta, and uterus.

A numbing medication may be applied to the abdomen to reduce pain, and the skin on the belly is disinfected with an antiseptic.

A needle is inserted, and ultrasound is used to help navigate the needle through the abdomen to reach the amniotic fluid. Afterwards the needle is extracted, and ultrasound can monitor any changes in the baby’s heart rate.

This test only takes about 15 minutes and normally causes only some discomfort or cramping.

After the test

It is best to avoid any strenuous activity for the first 24 hours after the procedure. If there are no complications, you are able to resume normal activities, including exercise and sexual intercourse.

Although serious side effects are uncommon, you may experience light cramping, minor vaginal bleeding, or some amniotic fluid that leaks from the vagina.

If you experience any of the following symptoms you should call your provider immediately:

  • Continuous bleeding or leakage of amniotic fluid from the vagina
  • Severe cramping that continues for more than a few hours
  • A temperature higher than 100.4 degrees Fahrenheit or 38 degrees Celsius

Complications are uncommon but can occur after amniocentesis. It is normal to have a small amount of amniotic fluid leakage, but large amounts of lost fluid can increase the risk for infection, preterm delivery, and other complications. In the past, patients were informed about a small risk of miscarriage, but recent studies indicate that this risk is extremely low and may not even be different from women who do not have an amniocentesis.

Amniocentesis Test Results

Receiving test results

For prenatal genetic tests the fetal cells must first be grown in the laboratory, meaning some results may be available within 7 days following the procedure, while other tests may take 2-3 weeks. Results for tests that are run on the fluid itself are typically available in less than 7 days. Ask your doctor about a realistic time frame for receiving your specific test results.

Amniocentesis test results will be given to you by a health care provider. For genetic tests, the results may be provided by a genetic counselor.

Interpreting test results

The reporting and interpretation of an amniocentesis test can depend on why the test was conducted. The doctor who ordered the test is in the best position to explain the results.

For prenatal chromosome analysis, the results are usually reported as “normal” or “abnormal” (with the specific abnormality being defined). For specific genetic disorders, test results may be reported as normal/negative or abnormal/positive. In some cases, additional testing may be requested to further clarify the results. It is important to remember that while amniocentesis can detect a variety of fetal chromosomal abnormalities and specific genetic disorders when there is a family history or known increased risk, it does not comprehensively check for all types of genetic changes or birth defects.

For testing performed on the amniotic fluid itself, such as AFP, AcHE, or viral antibodies to check for an infection, these results also are typically reported as positive (an abnormality was found) or negative (no abnormality was found).

Because there can be different types of amniocentesis tests, it is important to review the test results with a trained health care provider such as an OB-GYN, perinatologist, or prenatal genetic counselor, who can discuss why the test was performed and the significance of the results in your specific situation.

Are test results accurate?

Amniocentesis is a high-accuracy test that is generally considered to be the most reliable method of detecting certain types of abnormalities in an unborn baby. However, no test is perfect.

Do I need follow-up tests?

In many cases, amniocentesis is a diagnostic test that does not require further follow-up testing. However, in some situations, a repeat amniocentesis, additional blood tests, or other tests may be suggested in order to confirm a diagnosis or obtain more information about abnormalities detected during amniocentesis testing.

Questions for your doctor about amniocentesis test results

When going over amniocentesis test results with the doctor, the following questions may be helpful:

  • Did the test detect any genetic or chromosomal abnormalities?
  • If so, what type of abnormality is present?
  • What do the results mean for the fetus’s health and development?
  • Do you recommend that we talk to a genetic counselor?
  • Do I need any follow-up testing?

Related Tests

Amniocentesis vs. chorionic villus sampling

Amniocentesis and chorionic villus sampling (CVS) are both methods of detecting certain fetal abnormalities during pregnancy, but there are several notable differences between these tests.

Chorionic villus sampling is usually performed at 10 to 12 weeks of pregnancy, while amniocentesis is normally done after 15 weeks. Amniocentesis uses amniotic fluid as the sample for testing, while CVS uses a sample of tissue taken from the placenta.

One advantage of CVS is that it can identify certain genetic and chromosomal abnormalities earlier in the pregnancy. However, unlike amniocentesis, CVS does not measure AFP, AChE, or other substances that can detect spinal cord or brain defects.

Both procedures are performed with an ultrasound-guided needle. In amniocentesis, the needle is generally inserted through the abdominal wall. In chorionic villus sampling, the needle can be inserted through the abdominal wall or the cervix.

Sources

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American College of Obstetricians and Gynecologists. Amniocentesis. Updated March 2021. Accessed September 15, 2021. https://www.acog.org/womens-health/faqs/amniocentesis

Centers for Disease Control and Prevention. Birth defects during pregnancy: Prenatal testing. Updated October 27, 2020. Accessed September 15, 2021. https://www.cdc.gov/ncbddd/birthdefects/diagnosis.html

Dungan JS. Prenatal diagnostic testing. Merck Manual Consumer Version. Updated December 2019. Accessed September 15, 2021. https://www.merckmanuals.com/home/women-s-health-issues/detection-of-genetic-disorders/prenatal-diagnostic-testing

Dungan JS. Genetic evaluation. Merck Manuals Professional Version. Updated October 2019. Accessed September 15, 2021. https://www.merckmanuals.com/professional/gynecology-and-obstetrics/prenatal-genetic-counseling-and-evaluation/genetic-evaluation

Ghidini A. Diagnostic amniocentesis. In: Wilkins-Haug L, Levine D, eds. UpToDate. Updated September 2, 2021. Accessed September 15, 2021. https://www.uptodate.com/contents/diagnostic-amniocentesis

Ghidini, A. Patient education: Amniocentesis (beyond the basics). In: Lockwood CJ, ed. UpToDate. Updated September 2 2021. Accessed  October 14, 2021. https://www.uptodate.com/contents/amniocentesis-the-basics

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Jummaat F, Ahmad S, Mohamed Ismail NA. 5-Year review on amniocentesis and its maternal fetal complications. Horm Mol Biol Clin Investig. 2019;40(2):/j/hmbci.2019.40.issue-2/hmbci-2019-0006/hmbci-2019-0006.xml. Published 2019 Sep 20. doi:10.1515/hmbci-2019-0006

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