Amniocentesis involves inserting a needle into the abdomen to remove a small amount of the amniotic fluid surrounding the fetus. The fluid is then tested to diagnose or rule out a variety of birth defects such as Down syndrome, inherited genetic disorders, and neural tube defects. Because ultrasound is used during an amniocentesis, it can also detect some other types of birth defects, such as cleft palate and heart defects. The procedure is usually performed in the second trimester, between the 15th and 20th week of pregnancy.
Although you may still hear that the risk of miscarriage is between 1/200 and 1/400, those statistics were based on research done in the 1970s, when doctors didn’t have the latest ultrasound technology to help them guide the needle safely. The most recent study, which included 35,000 women at 15 hospitals around the country, found that the miscarriage risk associated with amniocentesis was only 1/1600.
In fact, women who chose to have the test were no more likely to have a miscarriage than women who decided not to have the test. Why? Pregnant women advised to consider amniocentesis are at a higher risk of having a baby with a genetic abnormality—either because they are 35 or older, they’ve have had positive results of a genetic screening test, or they have a family history of a genetic disease. Since most miscarriages occur spontaneously as the result of a chromosomal abnormality, women who are at higher risk but decide not to have an amniocentesis are still more likely to have a miscarriage, according to the authors of the study, led by Keith Eddleman, M.D., the Director of Obstetrics at Icahn School of Medicine at Mount Sinai, in New York City,
It’s normal for women to experience mild menstrual-like cramping during and after the procedure. Doctors generally say that women have about a 1/200 chance of having any sort of complication—including vaginal spotting or bleeding, leakage of amniotic fluid, severe cramping, fever, or infection. However, these usually resolve on their own, and there is no more than a 1/500 to 1/1000 chance that one of these could result in miscarriage, according to Dr. Eddleman.