Amniocentesis removes a small amount of fluid from the sac that surrounds the baby in the womb (uterus). It is usually done in a doctor's office or medical center. You do not need to stay in the hospital.
You will probably have a pregnancy ultrasound first. This helps your health care provider find out exactly where the baby is in your womb.
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.
The health care provider inserts a long, thin needle through your belly and into the womb. A small amount of fluid (about 4 teaspoons) is removed from the sac surrounding the baby.
The fluid is sent to a laboratory, where:
Genetic studies are done.
Levels of alpha-fetoprotein are measured.
Other tests may be done.
Results are usually back within 2 weeks.
How to Prepare for the Test
Your bladder must be full for the ultrasound.
Before the test, blood may be taken to determine your blood type and Rh factor. You may get a shot of medicine called RhoGAM if you are Rh negative.
How the Test Will Feel
Amniocentesis is most often offered to women at increased risk for bearing a child with birth defects. This includes women who:
Will be 35 or older when they give birth.
Had a screening test result that indicates a possible birth defect or other problem.
Have had babies with birth defects in previous pregnancies.
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.
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.
A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously reviewed by Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine (9/13/2011)