Dr. Vani Dandolu, an obstetrician-gynecologist at Temple University in Philadelphia, found that obesity, increasingly common in pregnant women, raises the risks to mother and baby.

Overweight and obese pregnant women are at higher risk of Caesarean section and are less likely to breastfeed, while their children are at higher risk of high birth weight and childhood obesity. Specifically, more than half of the overweight and obese women gained excessive weight during pregnancy. Further, more than half of the obese women had a Caesarean section, almost twice the rate of women with normal body mass indexes before pregnancy.

"While public education campaigns have increased the awareness of adverse effects of smoking and alcohol during pregnancy, there is limited public awareness regarding the harmful effects of high BMI during pregnancy," Dandolu said in a statement.

The study, published in the American Journal of Perinatology, analyzed information from a sample of 7,660 women and found 18 percent of mothers were obese, 13 percent were overweight, and 16 percent were underweight. Black non-Hispanic mothers were more likely to be obese and overweight than white non-Hispanic mothers. Older women who had previously given birth were more likely to be obese than younger women who had not.