Heavy moms, heavy newborns

It appears that women who begin their pregnancies overweight or gain too much during pregnancy put themselves and their newborns at greater risk for adverse health effects, according to a newly published study in the Canadian Medical Association Journal. In addition to having a higher risk of metabolic problems, a large newborn (meaning well over 8 lbs.) is more likely to cause birth injuries in the mother or to require a Cesarean section.

The study's findings are important, given that half of women who become pregnant in the U.S. may already be overweight or obese. Furthermore, the findings come at a time when experts are debating the link between gestational diabetes and high birth weight.

The conventional belief is that women with gestational diabetes elevated blood sugar levels during pregnancy but not otherwise are more likely to have a large baby, a result that has been blamed on their high blood sugar levels. Yet the current study, led by Dr. Ravi Retnakaran of Mount Sinai Hospital in Toronto, challenges this belief. After following 472 pregnant women, Dr. Retnakaran's research team found that those who were overweight before pregnancy, or who gained too much weight while pregnant, were more likely to have a "large-for-gestational-age" baby one that topped 8 pounds, 13 ounces. While the researchers found no clear link between elevated blood sugar and a heavy baby, there was a distinct correlation between the mother's weight and her baby's birth size. For every one-point increase in pre-pregnancy body mass index (BMI), a woman's odds of delivering a large baby rose by 16 percent. Similarly, for every kilogram a woman gained during pregnancy, her odds of having an oversized baby rose by 12 percent.

The findings may influence the conventional view of the relationship between gestational diabetes and high birth weight. If excess weight, as opposed to gestational diabetes, is indeed a better predictor of a high birth weight, acceptance of this finding could eliminate possibly unnecessary diabetes treatment for women who would otherwise be considered diabetic according to the new diagnostic criteria.

Of course, the best time to reduce one's weight to a healthful level is before pregnancy, experts say. Normal-weight women should expect to gain 25 to 30 pounds during pregnancy, but heavier women should gain much less.

Weight management on the part of the mother is also likely to be beneficial to the health of her child. There's some evidence that, later in life, oversized newborns face an increased risk for obesity, diabetes, and metabolic syndrome. As ACSH's Dr. Ruth Kava notes, "This study reinforces much previous data that indicate that maternal gestational weight gain and obesity are very important factors for not only infant size, but also for generational passage of obesity."