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Procedure: Amniocentesis

Description and Purpose

Also called amniotic fluid analysis , amniocentesis involves extracting a sample of fluid that fills the amniotic sac surrounding the baby, using ultrasound as a guide. The cells shed from the baby's skin and digestive tract found in the extracted sample are then cultured (grown in the laboratory), analysed and the results interpreted .
There are various reasons for such an analysis.

Preparation and Procedure

The test is usually performed between the 15th and 20th weeks of pregnancy. Ultrasound is often used to locate the placenta and make sure that there is sufficient amniotic fluid to extract a sample. A local anaesthetic may be applied to the stomach and while the mother lies on her back, a thin needle is inserted through the abdominal wall, and about a tablespoon of fluid is removed.
This procedure carries the risk of a miscarriage rate of 0.5% - 2%, injury to the foetus or placenta (very rare), bleeding, and infection. The risk is lowest when amniocentesis is performed at 14-16 weeks. A doctor should be contacted immediately if you experience abdominal cramps, vaginal bleeding, leakage of clear fluid from your vagina, unusual behaviour of the foetus, or anything else unusual.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. The Yale University School of Medicine Patient's Guide to Medical Tests, Barry L. Zaret M.D., Senior Editor, published by Houghton Mifflin. Online:

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Contact Last modified: Oct 20 2004