Scientists have found one more reason that pregnancy and obesity can be a bad combination.
A new study in the journal Pediatrics suggests that moms who are obese or have diabetes are more likely to have a child with autism or another developmental problem.
The finding is "worrisome in light of this rather striking epidemic of obesity" in the U.S., says Irva Hertz-Picciotto from the MIND Institute at the University of California, Davis, one of the study's authors.
But it's not clear whether there's any connection between rising obesity rates and the increasing number of children diagnosed with autism, she says.
The new study looked at about 1,000 mothers. Half of them had a child with an autism spectrum disorder, while the rest had a child with a developmental delay unrelated to autism, or no developmental problem.
Researchers wanted to know whether autism was more likely if a woman was obese, diabetic or had high blood pressure during pregnancy.
"We found that if women had one of these three conditions, the increased risk for her child was about 60 percent," Hertz-Picciotto says, though the overall risk was still relatively small.
These conditions also more than doubled the chance that a child would have some other developmental delay.
Obesity was the most common risk factor, affecting more than 20 percent of mothers with an autistic child. Also, obesity increases the risk that a woman will have diabetes during pregnancy, and can also increase the risk for high blood pressure.
"Obesity really affects the mother's physiology aside from the fact that she's carrying around a lot of extra weight," Hertz-Picciotto says.
The results also suggest that both obesity and diabetes are affecting early brain development, she says.
That could be because these conditions are associated with inflammation in developing tissues, including those in the brain, she says.
Another possibility is that obesity and diabetes are reducing the nutrients reaching the fetus by reducing the body's ability to use insulin, she says.
"We're talking about a fetal brain that could be suffering from a lack of oxygen," she says.
In the U.S., about one-third of women of child-bearing age are obese, and one child in 88 now has an autism spectrum disorder, according to government statistics.
So it's clearly a good idea for women who are overweight or obese to try to slim down before becoming pregnant, Hertz-Picciotto says. But she says people shouldn't assume that any particular child developed autism because of his or her mother's weight.