AmniocentesisDefinition: Amniocentesis is a test during pregnancy that removes a small amount of fluid from the sac around the baby to look for birth defects and chromosome problems.
Alternative Names: Culture - amniotic fluid; Culture - amniotic cells
How the test is performed: Amniocentesis is done on an outpatient basis. You do not need to stay in the hospital.
The doctor will find the exact location of the baby, usually by performing a pregnancy ultrasound .
The health care provider will clean an area of skin on the mother's belly area. A numbing medication (anesthetic) may be applied to the skin, or a local anesthetic may be injected into the skin.
The doctor inserts a long, thin needle through the abdomen and into the womb (uterus). A small amount of fluid is taken from the fluid-filled sac that surrounds the baby.
How to prepare for the test: Your bladder must be full for the ultrasound. There are no food or drink restrictions.
You may need to provide a blood sample to determine your blood type and Rh factor. You may get an injection of a medication called Rhogam if you are Rh negative.
You will need to sign a consent form before the test.
How the test will feel: If an anesthetic is used, you may feel a sharp, stinging sensation for a few seconds. When the needle enters the amniotic sac, you may feel a sharp pain lasting a few seconds.
Some women feel pressure in the lower abdomen when the fluid is pulled out. After the procedure, you may have some minor cramping.
Why the test is performed: The test can find chromosome problems such as:
Later on in a pregnancy, the test may be used to find problems such as:
This test is also sometimes done later in pregnancy to determine whether the baby's lungs are developed if there is a condition that requires early delivery.
Normal Values:
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean: Amniocentesis can be used to diagnose a large number of gene and chromosome problems in the baby. In addition, it can help:
- Determine how well the baby's lungs are developed
- Diagnose neural tube defects (such as spina bifida)
- Diagnose Rh incompatibility
DNA testing is available for many of the diseases that may be detected during amniocentesis. Ask your obstetrician or geneticist if you have a question about a specific disease.
What the risks are: Risks are minimal, but may include:
- Infection or injury to the baby
-
Miscarriage
- Leaking of amniotic fluid
- Vaginal bleeding
Special considerations: There may be alternatives to the amniocentesis. Discuss these other tests with your health care provider.
References: Simpson JL, Otaño L. Prenatal genetic diagnosis. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics:Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 7.
Druzin ML, Smith JF Jr, Gabbe SG, Reed KL. Antepartum fetal evaluation. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 11.
Cunnigham FG, Leveno KL, Bloom SL, et al . Prenatal diagnosis and fetal therapy. In: Cunnigham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 22nd ed. New York, NY; McGraw-Hill; 2005:chap 13.
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