Pregnant woman can cut excess weight gain by 20 percent if they switch to a low glycemic index diet, a new study says.

According to researchers mothers-to-be have a 48 percent chance of adding on extra pounds if they stick to their old diet but switching to a low glycemic index diet slashes that risk by 10 percent, bringing it to 38 percent.

"Our findings show that women who switch to a low GI diet during pregnancy are 20% less likely to experience excessive weight gain," said Fionnuala McAuliffe, Professor of Obstetrics and Gynaecology at the UCD School of Medicine and Medical Science, University College Dublin, and the National Maternity Hospital, Dublin.

Pregnant women who followed regular diets gained around 30 pounds during pregnancy compared to 26 pounds when women switched to low glycemic index diets.

The study included approximately 800 pregnant women who attended the National Maternity Hospital in Dublin. Of the participants, 400 women were randomly selected to switch to a low glycemic index diet that involved whole wheat bread, brown-rice and wholegrain foods.

The pregnant women weren't asked to reduce their calorie intake. These women attended education sessions that introduced them to the benefits of healthy eating. Also, these women met a dietician at 28 weeks and 34 weeks who reminded them of the importance of eating low-glycemic foods.

All the women were weighed before and after pregnancy and researchers measured their glucose levels. "Overall the 400 women on the low GI diet during their pregnancy reported that the diet was easy to follow and to shop for, and 80% said that they followed the diet all or most of the time," added McAuliffe.

"This type of excessive weight gain during pregnancy is associated with an increased need for delivery by Caesarean section, a higher likelihood of post pregnancy weight retention, and a higher predisposition to obesity in later life," added McAuliffe.

Previous research has shown that pregnant women benefit from eating a balanced diet and moderately exercising. Foods that have low glycemic index include fats, vegetables, fruits, legumes, raw starches and proteinswhile those that have high glycemic index include refined grains, refined sugars and certain fruits that have high amounts of sugars.

The results of this study show that low-GI foods are best for keeping off excess weight during pregnancy. However, it is always better that mothers-to-be consult a doctor before beginning any new diet or exercise.

The study was published in the journal BMJ.