Amniocentesis: MedlinePlus Medical Encyclopedia

P Amniocentesis is a test that can be done during pregnancy to look for these problems in the developing baby:
- Birth defects
- Genetic problems
- Infection
- Lung development 

T How the Test is Performed
P 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.
P You will have a pregnancy ultrasound first. This helps your health care provider see where the baby is in your womb.
P 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.
P Your health care 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.
P 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
P Results of genetic testing usually take about 2 weeks. Other test results come back in 1 to 3 days.
P 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)

T How to Prepare for the Test
P Your bladder must be full for the ultrasound.
P 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.

T Why the Test is Performed
P 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
P 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
P This test:
- Is a diagnostic test, not a screening test
- Is greater than 99% accurate for diagnosing Down syndrome
- Is most often done between 15 and 20 weeks
P 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)
- Down syndrome
- Rare metabolic disorders that are passed down through families
- Other genetic problems, like trisomy 18

T Normal Results
P A normal result means:
- No genetic or chromosome problems were found in your baby.
- Bilirubin and alpha-fetoprotein levels appear normal.
P Note: Even with normal amniocentesis results, a baby may still have genetic or other types of birth defects.

T What Abnormal Results Mean
P An abnormal result may mean your baby has:
- A gene or chromosome problem, such as Down syndrome 
- Birth defects that involve the spine or brain, such as spina bifida
P Talk to your health care 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

T Risks
P Risks are minimal, but may include:
- Infection or injury to the baby
- Miscarriage
- Leaking of amniotic fluid
- Vaginal bleeding

T Alternative Names
P Culture - amniotic fluid; Culture - amniotic cells; Alpha-fetoprotein - amniocentesis

T Images
- Amniocentesis
- Amniocentesis
- Amniocentesis - series

T References
P Simpson JL, Holzgreve W, Driscoll DA. Genetic counseling and genetic screening. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2012:chap 10.
P Simpson JL, Richards DA, Otao L, Driscoll DA. Prenatal genetic diagnosis. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2012:chap 11.

T Review Date 9/26/2015
P Updated by: Daniel N. Sacks MD, FACOG, obstetrics & gynecology in private practice, West Palm Beach, FL. Review Provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

