Women who are overweight or obese are more likely to deliver infants who are large for their gestational age at delivery, regardless of whether they develop gestational diabetes during their pregnancy, according to a study by Kaiser Permanente published August 14 in Diabetes Care.

Among pregnant women who did not develop gestational diabetes, overweight women were 65 percent more likely, and obese women 163 percent more likely, to have overly large babies than their healthy-weight counterparts. In this study, an overly large infant was identified based on having a birth weight over the 90th percentile for its gestational age at delivery and gender. Gaining excess weight during pregnancy also contributed to having a large-for-gestational-age baby, regardless of maternal weight or whether the mother developed gestational diabetes.

This Kaiser Permanente study of nearly 10,000 pregnant women from Kaiser Permanente Southern California examined adverse outcomes among women with and without gestational diabetes, as defined by the recently established International Association of Diabetes and Pregnancy Study Groups guidelines. Overly large babies are at increased risk for birth complications and for being overweight or obese later in life.

"Unhealthy pre-pregnancy body weight, gestational diabetes and excess weight gain during pregnancy are all contributors to problems during pregnancy and at delivery," said study lead author Mary Helen Black, PhD, of Kaiser Permanente Southern California's Department of Research & Evaluation. "It's possible that a large percentage of these problems may be prevented by helping overweight or obese women lose weight before they become pregnant or control their weight gain during pregnancy. Future intervention studies are needed to substantiate this."

Researchers examined the electronic health records of 9,835 women who received prenatal care and delivered their babies at the Kaiser Permanente Southern California Downey Medical Center (formerly called Bellflower Medical Center) over a five-year period from Oct. 30, 2005 to Dec. 31, 2010. Sixty percent of these women were overweight or obese and 19 percent developed gestational diabetes.

"By losing weight to achieve a healthy weight before pregnancy and by keeping their weight gain during pregnancy within guidelines established by the Institute of Medicine, women may decrease the health risks to their unborn babies and themselves," said study co-author David A. Sacks, MD, adjunct investigator at the Department of Research & Evaluation and a retired obstetrician-gynecologist from the Kaiser Permanente Downey Medical Center. "For children of overweight and obese women, the risks include an increased likelihood of having an excessive amount of body fat and being overweight or obese themselves, which can lead to high blood pressure, heart disease and type 2 diabetes later in life."