FAQ: Amniocentesis

What is amniocentesis?

Amniocentesis is a prenatal diagnostic test that can detect significant chromosome problems, such as Down syndrome, as well as small extra or missing pieces of chromosomes, called copy number variants. It can also identify genetic diseases like cystic fibrosis, sickle cell disease and Tay-Sachs disease in at-risk fetuses. Amniocentesis is typically performed between 15 and 20 weeks of pregnancy.

Doctors, nurses and other members of the health care team at the UCSF Prenatal Diagnosis Center bring a wealth of expertise and experience, having performed more than 40,000 amniocentesis procedures over the past 25 years.

What happens during the procedure?

Your complete visit to the UCSF Prenatal Diagnosis Center will take approximately two hours. First, you will meet with a genetic counselor who will assess your pregnancy history and family history, explain options for prenatal screening and testing, and address any questions or concerns you may have.

Then, you will have an ultrasound to assess the location of the fetus and the placenta, and to evaluate fetal growth. The actual amniocentesis procedure takes about 10 minutes and is done under ultrasound guidance. A needle is inserted through the abdomen to remove a small amount of amniotic fluid. Most women do not find the procedure painful, although there may be some minor discomfort.

The cells from the fluid are then cultured and a karyotype analysis, an evaluation of the chromosomes, is performed. The amniotic fluid is also tested to determine if the fetus has a defect in the tube enclosing the brain and spinal column. The results are available in about two weeks.

Are there any risks associated with the test?

There is a small risk of miscarriage as a result of an amniocentesis The miscarriage rate for procedures performed at UCSF is less than 1 in 350.

What does a positive result mean?

If you have a positive result, this means the test found a genetic abnormality. In these instances, you will have a chance to discuss the diagnosis and your options with an obstetrical geneticist and a genetic counselor from the Prenatal Diagnosis Center, as well as your own doctor. Referrals and support information are available for all decisions.

Will my insurance cover the cost?

Most insurance plans cover amniocentesis and other prenatal tests, especially for women over 35 years of age. You may need a referral from your primary care doctor or an authorization from your health plan to ensure insurance coverage. Our office staff is available to assist you with insurance questions.


Reviewed by health care specialists at UCSF Medical Center.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.