The number of babies born with Down syndrome rose by nearly
one-third from 1979 to 2003, a new study has found, likely because women are
waiting longer to have children.
Down syndrome went from affecting nine babies per 10,000 lives births in 1979 to 11.8 in 2003, according to the analysis, conducted by researchers at the Centers for Disease Control and Prevention and published in this month's Pediatrics.
The conventional wisdom is that as prenatal screening increases, the number of babies born with Down syndrome would fall as more couples choose to terminate pregnancies. The new numbers challenge this notion, though one Chicago pediatrician warned against reading too much into them.
Dr. Peter J. Smith, director of the developmental and behavioral pediatric program at the University of Chicago Medical Center, says changes in the way Down syndrome is reported could contribute to the increase.
"What we do know is that we're much better at counting people than we were in the 1970s," he says. Though Down syndrome seems like a straightforward diagnosis, like most people with disabilities, cases have been historically undercounted and hard to track.
There is no national registry for people with Down syndrome and genetic testing does not have to be reported.
"Whether there is a true increase or not, that's the million-dollar question," he says. "There's still a lot we don't know."
But recent demographic trends may hold the key.
Women over 35 are five times more likely to have babies with Down syndrome, and women over 35 are having a lot more kids than they were just a few decades ago. In 1990, 8.8 percent of new mothers were 35 or older, according to the CDC's National Vital Statistics System; in 2006, that number was 14.3 percent.
Scientists theorize that older uteruses may be less picky about which eggs get fertilized or that, sensing that this may be the last pregnancy, work harder to carry those pregnancies to term.
Gov. Sarah Palin gave birth to son Trig, who has Down syndrome, at age 44, when the chances of having a child with the condition is 1 in 35, according to the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
Smith says "political considerations" related to funding could influence how doctors and families of people with Down syndrome report the condition. With better prenatal genetic testing, many experts had predicted that rates would fall, potentially drying up funding for research and services.
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