Health Library

Amniocentesis - series

Indication

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, including those who:

• Will be 35 or older when they deliver.
• Have a close relative with a disorder.
• Had a previous pregnancy or baby affected by a disorder.
• Have 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.

Procedure, part 1

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.

Procedure, part 2

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 trained hands and under ultrasound guidance, the miscarriage rate may be even lower.

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.

Results

Amniocentesis helps in detecting or ruling out Down's syndrome, which causes intellectual disability, 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 intellectual disability.

If your pregnancy is complicated by a condition such as Rh-incompatibility, your doctor can use amniocentesis to find out if your baby's lungs are developed enough to endure an early delivery. Many more diagnoses are available through 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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