Mom's excess pounds key in newborn weight

For at least some moms-to-be, it's extra body fat - and not blood sugar levels - that may be key to their risk of having a big baby, a study published Tuesday suggests.

Researchers found that among 472 pregnant women they followed, those who were heavy before pregnancy or gained too many pregnancy pounds were more likely to have a "large-for-gestational-age" baby.

That meant having a newborn who topped 8 pounds, 13 ounces. Babies that large are more likely to cause birth injuries in the mom or to require a cesarean section.

Experts have long known that women who have gestational (pregnancy-related) diabetes are at increased risk of having a big baby. And the baby's weight is largely blamed on those mothers' high blood sugar levels.

The new findings suggest that for women without gestational diabetes, it's a mom's excess pounds that really matter in her baby's birth size, said lead researcher Dr. Ravi Retnakaran of Mount Sinai Hospital in Toronto.

"If we want to reduce the risk of having a big baby," he told Reuters Health, "the real gain would be in targeting the mother's weight."

Nearly half of pregnant women in the U.S. may start their pregnancies already overweight or obese. Recent research has found, though, that about half a percent, or 50 out of every 1,000 pregnant women, will develop gestational diabetes.

The new findings, which appear in the Canadian Medical Association Journal, come at a time when experts are debating whether they should lower the "threshold" blood sugar level for diagnosing gestational diabetes.

Canada has yet to adopt that approach. In the U.S., the American Diabetes Association has endorsed the proposal, but the American College of Obstetricians and Gynecologists is holding off on a decision: it's awaiting results from a conference to be held on the issue in October by the National Institutes of Health.

If the new criteria were adopted, Retnakaran said, about one-fifth of pregnant women in Canada would be "labeled" as having gestational diabetes - more than double the current rate.

But based on the current findings, he said, that label would not do those women any good - because it's weight, not moderately elevated blood sugar levels, that seems to be the "big predictor" of a big baby.

Dr. Edmond A. Ryan, a diabetes researcher at the University of Alberta in Canada, agreed.

For women who do not meet the traditional criteria for gestational diabetes, "obesity itself is actually more important than glucose (blood sugar)," said Ryan, who wrote an editorial published with the study.

So helping women manage their weight - ideally before pregnancy - is the key, according to Ryan. On the other hand, giving women the label of gestational diabetes could do more harm than good.