Is Down Up?

Here's something surprising that you may have missed: The number of children born with Down syndrome appears to be increasing.

A study published in the December issue of the journal Pediatrics concludes, "From 1979 through 2003, the prevalence of Down Syndrome at birth increased by 31% from 9.0 to 11.8 per 10,000 live births in 10 U.S. regions."

As NPR notes here, this goes against conventional expectations that prenatal screening would lead to a steep drop in the Down Syndrome population, as more parents opt to abort babies who test positive. While the study provides few details, author Adolfo Correa suggests the increase is a result of women waiting longer to have children. The likelihood of a Down Syndrome birth increases by a factor of five in mothers over 35. (Presumably it also increases the likelihood that a woman will decide to go ahead with the pregnancy anyway, in the belief that she won't get another chance.) The study says the increase "paralleled the increasing proportion of births to older mothers."

Interestingly, in a report just a few weeks earlier, Children's Hospital Boston pediatric geneticist Brian Skotko was quoted as saying there had been a 15 percent decrease in Down Syndrome births between 1989 and 2005. I'm not sure what data set he was drawing from, but Skotko also claimed that in the absence of prenatal screening we would have seen a 34% increase in DS births over that time period—remarkably close to the increase claimed by Correa.

So if an estimated 92% of all women who get a positive Down Syndrome result choose to terminate their pregnancies, how is the number of births increasing? It's tempting to say there are just more stubborn Sarah Palins out there than generally understood—and there is no shortage of moms who seize on the Pediatrics findings to speak out for their own decision to accept the "gift." The good news is that Americans with Down Syndrome, like all Americans, are living longer, healthier, fuller lives.

But it does raise some interesting questions about just how well we can predict any future patterns in human evolution. On the one hand you have a bunch of quacks insisting it's mathematically inevitable that redheads will become extinct around the time Al Gore's sea level rises by one full astronomical unit. On the other hand, you have a case where the means and motive for selection are available to everybody, and yet the trend is moving in the opposite direction from what the smart money predicted. Either futurists aren't listening to Jeff Goldblum or people are less predictable than advertised.

Of course the real question about folks with Down Syndrome remains: Are they happier than you and me? Devo investigates: