Pregnant women who keep their weight gain within guidelines reduce the risk that the baby will be too large, a risk factor for obesity, a new study concludes.

Since babies that are large-for-gestational age are known to face higher risks of heart and metabolic complications when they grown up, researchers are interested in exploring whether encouraging healthy diet and physical activity during pregnancy helps prevent those risks.

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By tracking weight during pregnancy, women and their doctors or midwives can reduce the likelihood of having a large baby. (iStock)

In Tuesday's online issue of the Journal of Maternal Fetal and Neonatal Medicine, Zach Ferraro, a PhD candidate in human kinetics based at the Children's Hospital of Eastern Ontario (CHEO) Research Institute and his co-authors say excessive weight gain during pregnancy predicts large babies, independently of whether the mother was overweight or obese before the pregnancy.

"We're really excited about the findings of this research," Ferraro said in an interview. "It's offering an avenue of support for all pregnant women that they can optimize the outcome of their baby by simply adhering to the recommendations."

The recommendations for weight gain in pregnancy are called the Institute of Medicine's gestational weight gain guidelines, which take into account a woman’s height and weight before pregnancy.

Compared with normal weight women who met the guidelines, both overweight and obese women who exceeded the guidelines had three to six times the chance of giving birth to a large baby, the researchers found.

"Obesity begets obesity without intervention," Ferraro said of the intergenerational cycle of weight gain that seems to have more than a genetic component to it.

Guide for all pregnant women

The Institute of Medicine guidelines offer "tremendous clinical value for primary care," the researchers concluded, since women and their providers can track and monitor weight status during pregnancy to reduce the likelihood of a large baby.

Instead of stigmatizing obesity and recognizing that some pregnant women are obese and healthy, these findings advise all pregnant women to gain weight appropriately.

"Birth weight averages can be an indicator of the weight a child will carry through preschool and even into adulthood," said Dr. Kristi Adamo, a co-author of the study and co-founder of the Healthy Active Living and Obesity (HALO) Research Group at the CHEO Research Institute.

"It's critical for a mother to understand that her healthy eating and lifestyle decisions during pregnancy will impact much more than a nine-month gestation period."

The study was based on a detailed look at data from 4,321 pairs of mainly Caucasian women and babies from Ottawa and Kingston.

Nearly 58 per cent of the women exceeded the gestational weight gain guidelines.

In this study, the researchers weren't able to control for factors like socioeconomic status and educational level. They are conducting a pilot trial to try to tease apart any cause-and-effect relationship between healthy eating and exercise during pregnancy and effects on newborns and children.

The study was funded by the Ontario Ministry of Research and Innovation, the Canadian Institutes of Health Research, the Ontario Women’s Health Council, and the Heart and Stroke Foundation of Canada.