Search the Health Library
Get the facts on diseases, conditions, tests and procedures.
I Want To...
I Want To...
Find Research Faculty
Enter the last name, specialty or keyword for your search below.
School of Medicine
Amniocentesis is a procedure performed to obtain genetic information about a developing fetus by collecting a sample of amniotic fluid — the fluid that cushions a baby in utero. The amniotic fluid contains cells that, when studied in a laboratory, can tell physicians if certain genetic conditions are present in the baby. Women usually undergo genetic counseling before having amniocentesis.
- Learn more about amniocentesis in the Johns Hopkins Health Library.
- Learn more about common tests during pregnancy in the Johns Hopkins Health Library.
Frequently Asked Questions
Why is an amniocentesis performed?
Your doctor may recommend an amniocentesis because of advanced maternal age (e.g., 35 or older), your family history, or because other prenatal screenings may have revealed a risk that the baby may have an inherited or congenital condition. Amniocentesis can also be used to test the amniotic fluid for signs of fetal infection or for a fetal protein known as alpha-fetoprotein, or AFP. AFP is used when checking for spina bifida (open spine defects).
What are the risks to my baby from an amniocentesis?
Any diagnostic procedure carries some risk. Your physicians and the genetic counselors at the Prenatal Diagnosis and Treatment Center at Johns Hopkins will explain the test and risks so you can make an informed decision about whether to proceed.
Who will perform the amniocentesis?
The procedure will be performed by an obstetrician/gynecologist and/or a maternal-fetal medicine provider. A sonographer will assist with the procedure.
When is this procedure performed?
This procedure is usually performed in or after the second trimester of pregnancy (starting at about 16 weeks gestation).
What can I expect during the amniocentesis?
Using ultrasound guidance, a thin needle is placed into the maternal abdomen and positioned within the amniotic fluid surrounding the fetus. A sample of amniotic fluid is obtained, which can then be sent for genetic testing.
Will I need to have a full bladder?
No, but sometimes a partially full bladder makes it easier to do the procedure, so we may advise you to not empty your bladder during your visit.
Where will the amniocentesis be performed?
Prior to the amniocentesis, you may have an ultrasound performed in the Prenatal Diagnosis and Treatment Center in an ultrasound suite. The amniocentesis will be performed in the same room.
What can I expect after the procedure?
You may have some mild cramping similar to menstrual cramps. This cramping may last for a few hours but should not last longer than 24 hours.
When will I get the results?
You will get the results in 10 to 14 days, in most cases, but it depends on what tests you are having.