Amniocentesis is the procedure for obtaining a small amount of amniotic fluid, which surrounds a developing baby during pregnancy to regulate temperature and provide protection from injuries. The clear, pale yellow-tinged fluid contains enzymes, proteins, hormones, and a variety of other substances including cells from the growing baby. The cells floating in the amniotic fluid contain genetic information. Collecting the fluid and cells with amniocentesis lets medical professionals diagnose chromosomal disorders and other potential health risks to the mother or baby.
A maternal serum -- or blood -- screening test is done before amniocentesis. Women using blood-thinning medications may need to stop taking them before the procedure and should follow any other doctors' instructions. A blood test determines blood type and Rh status (positive or negative). Amniocentesis to check for genetic abnormalities is usually done between the 15th and 20th week of pregnancy. If a woman is pregnant with twins or triplets, the doctor will perform amniocentesis for each baby inside of individual amniotic sacs. Identical twins share a single amniotic sac.
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