According to a new study, a woman’s weight before and during the pregnancy matters more than glucose level in predicting baby’s size. Being overweight or obese before and during pregnancy is the most reliable predictor of a woman’s risk of giving birth to a large baby, which can increase the chances of cesarean section and other complications during delivery.

The Canadian study of 472 women found that raised levels of blood glucose (sugar) and fats had little effect on the risk of having a big baby. A large baby is defined as a newborn whose weight is in the 90th percentile or above on Canadian fetal growth charts, or more than 8.8 pounds.

The findings support the importance of encouraging a healthy weight in young women as a way to reduce the risk of having a large baby. The study appeared online in CMAJ, the journal of the Canadian Medical Association.

Obstetricians typically focus on managing glucose levels in pregnant women with diabetes, to reduce their risk of having large babies. Recent studies have found a link between glucose levels in pregnant women even without gestational diabetes and the risk of having a larger baby.

The proposed new criteria from the International Association of Diabetes in Pregnancy Study Groups suggest a lower glucose level cutoff for diagnosing gestational diabetes to help identify women who may be at risk for having a large baby. However, the findings of this new study show that glucose levels are not a significant independent predictor of having a large baby.