Amnio: A Definitive Diagnosis
Performed between weeks 15 and 20, amniocentesis can conclusively diagnose neural-tube defects, Down syndrome and a host of other chromosomal defects. The procedure involves inserting a thin needle through the woman’s abdomen and into the amniotic sac to withdraw a sample of fluid.
Because it carries a very slight (1 in 200) risk of procedure-related miscarriage, doctors usually don’t perform amniocentesis unless risk factors or a patient’s age warrant it. (Because of their increased risk of having a baby with chromosomal defects, pregnant women age 35 and older are routinely referred for amniocentesis.) The results of an amnio usually take 10 to 14 days. Thus, in many cases, a patient’s mind can be put to ease by as early as 20 weeks.
“The hardest part is the waiting,” says Scott Copabianco, M.D., an obstetrician-gynecologist in Mission Viejo, Calif. “I know; I’ve been there.” His wife had a positive AFP test followed by amniocentesis with both of their children, who are now perfectly healthy 8- and 10-year-olds. He says the reason her numbers were high is still a mystery.
But Copabianco’s experience, both professional and personal, helps him reassure his patients that the vast majority of the time, everything is just fine.
The chances of having a false-positive alphafetoprotein (AFP) test increase with age: from 2.9 percent at 25 to 14 percent at 35 and to 40 percent at 40.