Amniocentesis is a diagnostic test that checks for genetic birth defects like Down syndrome and trisomy 18. Usually done between 16 and 18 weeks, the procedure involves inserting a needle through your belly to remove some amniotic fluid (which has the same genetic makeup as your baby) to be tested in a lab. Amnios are usually offered to women 35 or older (because your chances of genetic problems increase with age) and to women who've had a previous pregnancy where there was a genetic defect, who have a family history of certain conditions, or who have already had an abnormal test result from a CVS (chorionic villus sampling), nuchal translucency ultrasound, or multiple marker screening.
The biggest risk associated with having an amnio is miscarriage, but with recent advances in testing procedures, this is much lower than experts used to believe -- as little as one in 500. Many doctors feel that, for some couples, the benefits of having vital, conclusive information about their baby's health outweighs this risk. Most often amnio results provide precious peace of mind, but in the rare situation that there's a problem, they can also give the parents of a baby with special needs time to plan and become educated about caring for their child emotionally and financially.
Deciding whether or not to have the test raises some difficult questions. For example, if you discovered that your baby had Down syndrome, would you choose to not continue with the pregnancy? It can be difficult to wrap your head around these tough decisions, and if you're unsure, seeing a genetic counselor with your partner can help you weigh the pros and cons and decide what's best for your family. If you're concerned about the invasiveness of the test, talk to your doctor about what other tests, like a nuchal ultrasound or multiple marker screening, have revealed. That may give you enough information to decide whether further testing may be needed.