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Mom's weight, not blood sugar levels, may lead to birth of large baby

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(CBS News) A mother's weight before and during pregnancy may be more of an indicator that she will give birth to a big baby than her blood glucose levels, new research reveals.

According to the study, slightly high blood glucose levels -- not enough to diagnose the mother with gestational diabetes according to Canadian standards -- had no association with having a larger bundle of joy once weight was taken into an account.

The new study, published in the May 22 issue of the Canadian Medical Association Journal, contradicts some current thoughts on why babies are born overweight. Many experts believe that gestational diabetes is the most common cause of macrosomia, the name for when a fetus is "abnormally large" and weighs 8 pounds, 13 ounces or more at birth, according to the NYU Langone Medical Center. For the purposes of the study, a large baby was defined as one who placed in the 90th percentile for his or her race, size and weight according to gestational age.

The ADA recently lowered its blood sugar level threshold for gestational diabetes because it said previous standards only accounted for women's risk of developing diabetes in the future and didn't include risks to the mother or baby, including a overly heavy birth weight, according to Science Daily. According to a Feb. 2010 report in Diabetes Care - a journal of the American Diabetes Association - mothers who had gestational diabetes according to the lower standards had a 50 percent chance of having an overweight baby. They estimate that 18 percent of expecting mothers have disease according to the lower threshold.

However, the U.S. and Canada have not adopted the ADA's levels yet, and the American College of Obstetricians and Gynecologists is holding off on their decision until a conference in October 2012 on the issue, according to Reuters. The World Health Organization (WHO) is also debating whether to accept the new regulations.

Researchers analyzed data on 472 pregnant women. Out of the group, 368 had normal glucose levels and 104 had slightly elevated glucose levels or gestational impaired glucose tolerance.

Sixty-eight of the infants born to these women were large for their gestational age at delivery. The mothers who were overweight before they got pregnant or gained excess weight during pregnancy were 12 to 16 percent more likely to have large babies. The subject's glucose levels and levels of fatty acids in the blood did not seem to factor. The study did not rule out that gestational diabetes may cause the birth of a large baby because none of the people tested had gestational diabetes.

"Lowering the criteria (for gestational diabetes) might not be targeting the appropriate problem," study author Dr. Ravi Retnakaran, a diabetes researcher at Mount Sinai Hospital in Ontario, told MyHealthNewsDaily.

"The rate of obesity has increased so much that maybe glucose levels aren't as big a factor as they once were," he added.

Having a large baby, otherwise known as macrosomia, comes with its share of risks. For the mother, there's an increased risk of perineal tearing and blood loss, according to Medscape. More than likely, mothers will have to undergo a cesarean delivery. The baby may get stuck behind the pubic bone -- otherwise known as shoulder dystocia -- a serious yet rare situation. In that case, doctors may have to break the baby's collarbone or clavicle to get it out, which should eventually heal.