Amniotic fluid surrounds the baby during pregnancy. As the baby grows, cells from the baby are shed into this fluid. Amniocentesis is the removal of a small amount of the fluid for testing.
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Reasons for Procedure
Cells found in the fluid can be used to examine the baby's genes. The test may be done if your baby has a high risk of a birth defect. They can also show if the baby is developing as expected. Depending on your risk factors, cells in the amniotic fluid are tested for:
- Chromosome (DNA) abnormalities—missing or extra chromosomes lead to physical birth defects and/or intellectual disability such as Down syndrome
- Inherited genetic diseases—Examples include:
Later in pregnancy, an amniocentesis may be done to:
- Look for infection of the fluid
- Make sure the baby's lungs are developed enough for the baby to breathe on their own (in high-risk pregnancies that may require early delivery of the baby)
- Look for Rh-sensitization—when mother and baby have different blood types
An amniocentesis may be recommended:
- If mother is over 35 years of age at the time of delivery
If there is a family history of:
- Chromosome abnormality
- Inherited disorder
- Problems in spine and brain growth (known as a neural tube defect)—problems in spine and brain growth, such as spina bifida or anencephaly
- After abnormal results from other early screening tests for chromosomal (DNA) abnormalities or a neural tube defect
Your doctor can help you understand the pros and cons of having this test.
Problems from the procedure are rare, but all procedures have some risk. Your doctor will review potential problems, like:
- Bleeding, cramping, and leaking fluid from the vagina
- Mixing of blood if you and your baby have different blood types
- Need for repeat testing
- Harm to the fetus by the needle—rare
- Miscarriage —rare
Factors that may increase your risk of complications include:
- Maternal obesity
- Previous abdominal surgery
Be sure to discuss these risks with your doctor before the procedure.
What to Expect
You may be given a local anesthesia. This numbs a small area in the abdomen where the needle will be placed.
Description of the Procedure
An ultrasound will be used during the procedure. This will allow your doctor to see where the needle is. Your belly will be cleaned. A very thin needle will be inserted through your skin into your uterus. A few teaspoons of amniotic fluid will be removed and the needle will be pulled out. The doctor will make sure that your baby's heartbeat is normal.
How Long Will It Take?
About 45 minutes
Will It Hurt?
You may feel cramping when the needle enters your abdomen. You may also feel pressure when the fluid is withdrawn.
A test showing a healthy baby is ideal, but you will need to be prepared if the results are abnormal. If there is a disorder, further counseling can be helpful. Your doctor will work with you on options that are best for you after you know the results.
- Chromosome (DNA) abnormalities. The results are usually ready within 14 days.
- Inherited genetic diseases—Test results are usually ready in 1-5 weeks. Examples include:
Call Your Doctor
It is important to monitor your recovery. Alert your doctor to any problems. If any of the following occur, call your doctor:
- Signs of infection, including fever and chills
- Nausea or vomiting
- Pain or cramping in your lower abdomen or shoulder
- Vaginal bleeding or a leaking of fluid from the vagina
- Redness, swelling, increasing pain, excessive bleeding, or discharge from the amniocentesis site
- New, unexplained symptoms
If you think you have an emergency, call for medical help right away.
American Congress of Obstetricians and Gynecologists
American Pregnancy Association
Canadian Women's Health Network
The Society of Obstetricians and Gynaecologists of Canada
Chorionic villus sampling (CVS). American Pregnancy Association website. Available at: http://www.americanpregnancy.org/prenataltesting/cvs.html. Updated July 2015. Accessed March 14, 2015.
Hemolytic disease of the fetus and newborn (HDFN). EBSCO DynaMed Plus website. Available at:http://www.ebscohost.com/dynamed. Updated April 4, 2016. Accessed October 7, 2016.
Later childbearing. American College of Obstetricians and Gynecologists website. Available at: http://americanpregnancy.org/prenatal-testing/chorionic-villus-sampling. Updated July 2015. Accessed March 14, 2016.
Routine prenatal care. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T114252/Routine-prenatal-care. Updated June 22, 2016. Accessed October 7, 2016.
The American Congress of Obstetricians and Gynecologists, Invasive Prenatal Testing for Aneuploidy, Practice Bulletin No. 88, December 2007; Reaffirmed 2014.
Zolator AJ, et al. Update on prenatal care. Am Fam Physician. 2014 Feb1;89 (3): 199-208.
Last reviewed March 2018 by EBSCO Medical Review Board Beverly Siegal, MD, FACOG Last Updated: 3/28/2018