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Amniocentesis is the name of the procedure in which a thin needle is inserted into the uterus to withdraw a small amount of amniotic fluid. The fetal skin cells found in the fluid are then analyzed for chromosomal abnormalities.

Most women who are recommended for an "amnio" fall into two large categories. Either they have received an abnormal result on the AFP screening test, or they are age 35 or older. Maternal age is an important risk factor for Down's syndrome; the incidence increases as maternal age increases. Furthermore, beginning with age 35, the risk of having a child with Down's syndrome exceeds the risk of injuring the pregnancy by the procedure. Under age 35, there is a greater risk of causing injury than there is of diagnosing a problem. Because of this risk, amniocentesis is not recommended for women under 35 unless the AFP result is abnormal.

It's hard not to be nervous about having an amnio, but it's actually a short and simple procedure. The entire process takes about 60 seconds. If you're like most people, your anxiety centers around the needle; many women are intimidated by its length. It's important to remember, though, that the amount of discomfort associated with a needle is related to the thickness of the needle, not the length. A very thin needle is used in amniocentesis; this minimizes possible injury to the fetus and decreases maternal discomfort.

Your doctor generally performs the amnio, and the procedure is always guided by ultrasound. This means the ultrasonographer monitors everything that happens, and guides your doctor in the placement of the needle. The risk of injury to the fetus is therefore very small.

Before beginning the ammo, the ultrasonographer does a complete evaluation of the fetus, just as if you were having a routine ultrasound. This time, though, he or she pays special attention to the fetus's location in the uterus. The ultrasonographer looks for a large "pocket" of fluid-a space where the needle can be inserted without coming close to the fetus. Some babies are more cooperative then others. Your baby might want to play tricks; every time a pocket is found, he or she might move into it, requiring a search for another pocket.

Once the pocket of fluid is identified, the ultrasonographer tells your doctor where the needle should be placed. Then, the overlying skin is "prepped" with betadine solution to minimize the risk of infection, and the doctor inserts a long, thin needle through the abdominal wall into the amniotic sac. He or she then withdraws a small amount of amniotic fluid and removes the needle. If you want to, you can watch the entire procedure.

The amniotic fluid that has been removed is sent to a special genetics laboratory. The fetal skin cells in the amniotic fluid, which have been shed during normal growth, are encouraged to grow and divide. Geneticists analyze the cells for the presence of chromosomal abnormalities. Growing the fetal cells and analyzing them can take anywhere from ten days to two weeks.