Health: Is Amnio Right For You?

During Audrey Fosse's first two pregnancies, at ages 30 and 33, early screening tests revealed she had higher-than-average odds of delivering a baby with Down syndrome. Both times, her obstetrician recommended she have amniocentesis, a diagnostic test that determines if a woman is carrying a baby with a chromosomal abnormality. But the test has an often-cited miscarriage rate of one in 200. "It was a little bit scary because you did know there were risks involved," says Fosse. "But we wanted the reassurance that everything was okay--or, if it wasn't okay, that we would be prepared for that." Her results were normal, and she delivered healthy children.

It turns out Fosse was ahead of her time in using more than just her age to help her decide whether to get amnio 15 weeks or so into her pregnancy. A paper in the November issue of the Journal of Obstetrics and Gynecology, part of a major National Institutes of Health-funded study on pregnancy screening, reports that the risk of miscarriage from the $1,200 procedure, in which a doctor inserts a needle into the uterus through the skin of the belly to extract a sample of amniotic fluid, may be as low as one in 1,600. "The loss rate is way, way, way less than we thought it was," says Dr. Gary Hankins, chair of the American College of Obstetricians and Gynecologists' obstetrics-practice committee. (The study did not look at chorionic villus sampling, the other definitive test for Down syndrome.)

For three decades, 35 has been the magic age at which doctors counseled pregnant women to consider amniocentesis. Now, "that number is outdated," says Mount Sinai School of Medicine's Dr. Keith Eddleman, the study's lead author. The logic behind the guidelines: only at 35 did a woman's risk of delivering a baby with a chromosomal abnormality (one in 192) seem to outweigh her risk of having a miscarriage from amnio. If you apply that thinking to the new study results, even a 20-year-old, whose risk of delivering a baby with Down syndrome is just one in 1,667, might consider the procedure. Not many doctors would recommend that, citing cost and believing the miscarriage risk lies somewhere between one in 200 and the latest figures. "Most people would agree that that's probably an overoptimistic number," says Columbia University Medical Center's Dr. Ronald Wapner. "However, I do believe that amnios are much safer than the one-in-200 risk that we have given patients."

So, who should undertake amnio now? A woman who wants a decisive result. "Some women say, 'No matter how low the risk of Down syndrome, I want to have an amnio'," says Dr. Allan Nadel of Massachusetts General Hospital. Bear in mind that miscarriage rates vary among practitioners. "Ask the person how frequently they perform the test. I would look for someone who does 50 or more a year," says the University of Chicago's Dr. Marion Verp. For Fosse, it was the right choice.