Amniocentesis

Culture - amniotic fluid; Culture - amniotic cells; Alpha-fetoprotein - amniocentesis

Amniocentesis is a test that can be done during pregnancy to look for certain problems in the developing baby. These problems include:

Birth defects
Genetic problems
Infection
Lung development

How the Test is Performed

Amniocentesis removes a small amount of fluid from the sac around the baby in the womb (uterus). It is most often done in a doctor's office or medical center. You do not need to stay in the hospital.

You will have a pregnancy ultrasound first. This helps your health care provider see where the baby is in your womb.

Numbing medicine is then rubbed onto part of your belly. Sometimes, the medicine is given through a shot in the skin on the belly area. The skin is cleaned with a disinfecting liquid.

Your provider inserts a long, thin needle through your belly and into your womb. A small amount of fluid (about 4 teaspoons or 20 milliliters) is removed from the sac surrounding the baby. In most cases, the baby is watched by ultrasound during the procedure.

The fluid is sent to a laboratory. Testing may include:

Genetic studies
Measurement of alpha-fetoprotein (AFP) levels (a substance produced in the liver of the developing baby)
Culture for infection

Results of genetic testing usually take about 2 weeks. Other test results come back in 1 to 3 days.

Sometimes amniocentesis is also used later in pregnancy to:

Diagnose infection
Check whether the baby's lungs are developed and ready for delivery
Remove excess fluid from around the baby if there is too much amniotic fluid (polyhydramnios)
Polyhydramnios
Polyhydramnios occurs when too much amniotic fluid builds up during pregnancy. It is also called amniotic fluid disorder, or hydramnios.
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How to Prepare for the Test

Your bladder may need to be full for the ultrasound. Check with your provider about this.

Before the test, blood may be taken to find out your blood type and Rh factor. You may get a shot of medicine called Rho(D) Immune Globulin (RhoGAM and other brands) if you are Rh negative.

Why the Test is Performed

Amniocentesis is usually offered to women who are at increased risk of having a child with birth defects. This includes women who:

Will be 35 or older when they give birth
Had a screening test that shows there may be a birth defect or other problem
Have had babies with birth defects in other pregnancies
Have a family history of genetic disorders

Genetic counseling is recommended before the procedure. This will allow you to:

Learn about other prenatal tests
Make an informed decision about options for prenatal diagnosis

This test:

Is a diagnostic test, not a screening test
Is most often done between 15 to 20 weeks of your pregnancy, but can be performed at any time between 15 to 40 weeks

Amniocentesis can be used to diagnose many different gene and chromosome problems in the baby, including:

Anencephaly (when the baby is missing a large portion of the brain)
Anencephaly
Anencephaly is the absence of a large part of the brain and the skull.
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Down syndrome
Rare metabolic disorders that are passed down through families
Other genetic problems, like trisomy 18 (also known as Edwards syndrome)
Infections in the amniotic fluid

Normal Results

A normal result means:

No genetic or chromosome problems found in your baby.
Bilirubin and alpha-fetoprotein levels appear normal.
No signs of infection found.

Note: Amniocentesis typically is the most accurate test for genetic conditions and malformation, although rare, a baby may still have genetic or other types of birth defects, even if amniocentesis results are normal.

What Abnormal Results Mean

An abnormal result may mean your baby has:

A gene or chromosome problem, such as Down syndrome or trisomy 18
Down syndrome
Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.

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Birth defects that involve the spine or brain, such as spina bifida
Spina bifida
Myelomeningocele is a birth defect in which the backbone and spinal canal do not close fully before birth. The condition is a type of neural tube de...
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Talk to your provider about the meaning of your specific test results. Ask your provider:

How the condition or defect may be treated during or after your pregnancy
What special needs your child may have after birth
What other options you have about maintaining or ending your pregnancy

Risks

Risks are minimal, but may include:

Infection or injury to the baby
Miscarriage
Miscarriage
A miscarriage is the spontaneous loss of a fetus before the 20th week of pregnancy. Pregnancy losses after the 20th week are called stillbirths. Mi...
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Leaking of amniotic fluid
Vaginal bleeding

Open References

References

Driscoll DA, Simpson JL. Genetic screening and diagnosis. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 10.

Dugoff L, Wapner RJ. Prenatal diagnosis of congenital disorders. In: Lockwood CJ, Copel JA, Dugoff L, et al, eds. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2023:chap 30.

Patterson DA, Andazola JJ. Amniocentesis. In: Fowler GC, eds. Pfenninger and Fowler's Procedures for Primary Care. 4th ed. Philadelphia, PA: Elsevier; 2020:chap 144.

Amniocentesis - illustration
Amniocentesis is used to determine the health of an unborn baby. Amniotic fluid contains cells that are normally shed from the fetus. Samples of these cells are obtained by withdrawing some amniotic fluid. The chromosome analysis of these cells can be performed to determine abnormalities. In addition, the cells may be cultured and analyzed for enzymes, or for other materials that may indicate genetically transmitted diseases. Other studies can be done directly on the amniotic fluid including measurement of alpha-fetoprotein.
Amniocentesis
illustration
Amniocentesis - illustration
In amniocentesis a hollow needle is inserted into the mother's abdomen into the uterus, and amniotic fluid is drawn for analysis.
Amniocentesis
illustration
Amniocentesis - series - Indication
Presentation

<strong>Amniocentesis - series - Indication</strong><p>When you are about 15 weeks pregnant, your doctor may offer amniocentesis. Amniocentesis is a test that detects or rules out certain inherited disorders in a fetus. It also assesses lung maturity to see if the fetus can endure an early delivery. You can also find out the baby's sex. Doctors generally offer amniocentesis to women with an increased risk of having a baby with particular disorders. The procedure may be offered to women who will be 35 or older when they deliver, have a close relative with a disorder, or had a previous pregnancy or baby affected by a disorder. It may also be offered if a woman has test results (such as a high or low alpha-fetoprotein count) that may indicate an abnormality. Doctors also offer amniocentesis to women with pregnancy complications, such as Rh-incompatibility, that necessitate early delivery. There are blood tests and ultrasound tests that can be done earlier in the pregnancy which may avoid the need for amniocentesis at times.</p>

<strong>Procedure, part 1</strong><p>Amniocentesis is done in an examination room, either with or without local anesthesia. It typically takes just a few minutes, during which you must lie very still. A technician locates your fetus with an ultrasound. Using the ultrasound for guidance, your doctor carefully inserts a long, but thin, hollow needle through your abdomen and into the amniotic sac. You should receive Rh immune globulin (RHIG) at the time of amniocentesis if you are an Rh-negative unsensitized patient.</p>

<strong>Procedure, part 2</strong><p>The doctor then extracts about four teaspoons of amniotic fluid. This fluid contains fetal cells that a technician grows in a lab and analyzes. Test results are generally available in two to three weeks. Doctors recommend you rest and avoid physical strain (such as lifting) after amniocentesis. If you experience any complications after the procedure, including abdominal cramping, leakage of fluid, vaginal bleeding, or signs of infection, call your doctor immediately. There is between a 0.25% and 0.50% risk of miscarriage and a very slight risk of uterine infection (less than .001%) after amniocentesis. In most cases, your test results will be available within two weeks. Your doctor will explain the results to you and, if a problem is diagnosed, give you information about ending the pregnancy or how best to care for your baby after birth.</p>

<strong>Results</strong><p>Amniocentesis helps in detecting or ruling out Downs syndrome, which causes mental retardation, congenital heart defects, and physical characteristics such as skin folds near the eyes. Amniocentesis also detects neural tube defects such as spina bifida. Babies born with spina bifida have a backbone that did not close properly. Serious complications of spina bifida can include leg paralysis, bladder and kidney defects, brain swelling (hydrocephalus), and mental retardation. If your pregnancy is complicated by a condition such as Rh-incombatibility, your doctor can use amniocentesis to find out if your babys lungs are developed enough to endure an early delivery. Many more diagnoses are available through amniocentesis.</p>

Amniocentesis - illustration
Amniocentesis is used to determine the health of an unborn baby. Amniotic fluid contains cells that are normally shed from the fetus. Samples of these cells are obtained by withdrawing some amniotic fluid. The chromosome analysis of these cells can be performed to determine abnormalities. In addition, the cells may be cultured and analyzed for enzymes, or for other materials that may indicate genetically transmitted diseases. Other studies can be done directly on the amniotic fluid including measurement of alpha-fetoprotein.
Amniocentesis
illustration
Amniocentesis - illustration
In amniocentesis a hollow needle is inserted into the mother's abdomen into the uterus, and amniotic fluid is drawn for analysis.
Amniocentesis
illustration
Amniocentesis - series - Indication
Presentation

Self Care

Tests for Amniocentesis

Amniocentesis

Review Date: 8/23/2023

Reviewed By: LaQuita Martinez, MD, Department of Obstetrics and Gynecology, Emory Johns Creek Hospital, Alpharetta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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Health Library

Amniocentesis

How the Test is Performed

Pregnancy ultrasound

Polyhydramnios

How to Prepare for the Test

Blood type

Why the Test is Performed

Anencephaly

Normal Results

What Abnormal Results Mean

Down syndrome

Spina bifida

Risks