A new study this week linking motherhood obesity to childhood autism tells a seemingly horrible tale: pregnant women who are obese are 67 percent more likely to have a child who suffers from the disorder than her non-obese counterpart. It's the kind of statistic that people latch on to, and dozens of stories in the media highlighted the stat.
But what can we actually make of such a figure? 67 percent sounds like a big deal. You're well on your way to doubling your risk, it seems. But without context, it's hard to gauge how much maternal obesity matters relative to the host of author autism risk facts.
While the 67 percent figure is "non-trivial," according to Dr. William Eaton, a professor of mental health at Johns Hopkins University, maternal obesity isn't exactly considered a leading risk factor. There are others that raise the risk for childhood autism by roughly the same amount, and still others that cause it to skyrocket.
For example, when a baby comes out of the womb feet-first, "a breech birth," the child's risk for autism increases about 63 percent. Babies with an Apgar score -- an indicator, from one to ten, of a child's relative health five minutes after birth -- of less than seven are about 89 percent more likely to be autistic, Eaton said.
"There are some studies about autism which have much stronger risk factors," Eaton added, "with hazard ratios like two or three or four," that is to say, a 200 or 300 or even 400 percent increase in risk.
Some of these more serious risk factors are simply out of our control. A child born before 35 weeks carries two and a half times the risk for autism. Family mental history can also play a role. If someone in your family suffers from psychosis or a mood disorder, the risk for childhood autism increases two to three times.
So, maternal obesity may be a risk factor for autism, but it's important to remember that it's only one among many and not even the strongest link.
And, Eaton said, separating out obesity, itself, from other linked disorders is a challenge in itself. "Just to show you how complicated things are, obese women could have a higher rate of mood disorder," he said. "And we wouldn't know if it was the mood disorder doing the work or the obesity."