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Amniocentesis

Often referred to as an "amnio," this test is usually done between 15 and 21 weeks. With an accuracy rate as high as 99 percent, an amniocentesis can detect Down syndrome, other chromosomal disorders, and genetic glitches, including Tay-Sachs disease, cystic fibrosis, and sickle-cell anemia. It's generally offered to women over 35 because that's the age at which the risk of chromosomal abnormalities is approximately equal to the risk of the procedure. However, new data show the risk of miscarriage after amniocentesis is much lower.

How it's done. This is one of those tests that's scary in principle, but in fact it doesn't hurt much and usually has few side effects. Some women fear an amniocentesis because it involves a larger-than-life needle inserted into the abdomen. They may worry about the pain of the needle or be concerned that the procedure might harm their baby or cause pregnancy complications. Still others are anxious about the small risk of miscarriage associated with amniocentesis. Most of the time, these fears are unfounded, and your provider will recommend an amniocentesis when the benefits of having the test outweigh the risks.

There are no restrictions on what you can eat or drink beforehand. You'll lie on your back on a table while the practitioner does an ultrasound to determine the position of the baby. Next she will clean off an area on your belly with antiseptic solution. Many doctors do not use anesthetic because the numbing medicine is sometimes worse than the quick, thin amniocentesis needle.

Your provider will insert a long, hollow needle through your abdomen into the uterus and amniotic sac to draw a sample of amniotic fluid. You probably won't feel anything other than the pinprick, followed by a tugging or pushing sensation of the actual amniocentesis needle. Your amniotic fluid contains free-floating fetal cells that can be grown in a laboratory; at the lab, technicians will extract chromosomes or genes from these cells and analyze them for various abnormalities. It generally takes about 2 weeks to get the results of this analysis. The amount of amniotic fluid that is removed is generally replenished within the next 24 hours.

Risks. Because the ultrasound allows the technician to see the position of your baby, the chances of your baby being harmed by the needle are minuscule. The main negative side effect of an amniocentesis is miscarriage, but that happens to fewer than 1 in 200 women who have this test. In addition, about 1 percent of women experience bleeding, cramping, or leaking fluid from the vagina after the procedure. These symptoms usually resolve on their own. Therefore, the overall risk of an amniocentesis to you and your baby is low.

Originally published in You & Your Baby: Pregnancy.

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