Birthing a normal-sized baby naturally is more likely to occur for women who exercise during their pregnancies, according to a new study.

"We found that women who exercised had a 31 percent reduction in the risk of having a large baby without changing the risk of having a small baby or an earlier baby," says lead researcher Margie Davenport, an assistant professor in the Faculty of Physical Education and Recreation at the University of Alberta in Canada.

What's more, the risk of needing a Caesarean section was reduced by 20 percent for women who had exercised during pregnancy, the study concludes.

The study, which was published in the journal Obstetrics & Gynecology, has important implications because mounting evidence suggests babies born large tend to be heavier throughout their lives.

The research team conducted a meta-analysis, analyzing 28 studies that included data on 5,322 pregnancies.

All of the studies compared women on supervised prenatal exercise programs to those who received standard care.

For participants in all studies who were given supervised exercise interventions, they completed at least one session every two weeks during pregnancy.

Studies involving only pelvic floor exercise interventions were excluded from the meta analysis.

The Center for Disease Control has earmarked a normal birth weight as being between 5.5 lbs. (2.49 kg) and 8.8 lbs. (3.99 kg).

Babies born too big are at a greater risk of autism, according to a 2013 study conducted in the UK.

Mounting evidence suggests birth weight could be an indicator of body mass index over the course of a lifetime.

Even if the mother is not obese, a high birth weight could mean the baby will grow into an overweight or obese child and possibly stay that way into adulthood, according to a study from the University of North Carolina in the US.