BSIP LAURENT / SCIENCE PHOTO LIBRARY BSIP LAURENT / SCIENCE PHOTO LIBRARY
Amniocentesis. A doctor performs an amniocentesis test on a pregnant woman. In this procedure a small amount of amniotic fluid is drawn through a needle from the amniotic sac - the membranous bag that surrounds the foetus in the uterus. An ultra- sound scanner (right) is used to work out where to puncture the womb. Foetal cells in the amniotic fluid can be screened for chromosomal or genetic disorders, such as Down's syndrome, haemophilia or cystic fibrosis. The test is usually performed at 16-18 weeks into pregnancy and no anaesthetic is required. Because of risks associated with this test, amniocentesis is only recommended for women where the chance of a foetal disorder is high.
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