The benefits of exercise during pregnancy

Historically, women were discouraged from vigorous exercise during pregnancy because of the risk of preterm birth. "The thinking was that exercise releases norepinephrine in the body, which is a chemical that can stimulate contractions of the uterus, and thus lead to preterm birth," says senior author on the study Vincenzo Berghella, M.D., Director of Maternal Fetal Medicine and Professor at the Sidney Kimmel Medical College at Thomas Jefferson University. "But numerous studies including this new meta-analysis, have since shown that exercise does not harm the baby, and can have benefits for the mom and baby."

Dr. Berghella and his co-authors pooled data from nine randomized controlled studies -- one of the strongest types studies involving human subjects -- in which pregnant women were divided into two groups. Of the 2,059 women who were included in the analysis, about half (1,022 women) exercised for 35-90 minutes 3-4 times per week for 10 weeks or up until their delivery, whereas the other half, (1,037 women) engaged in no exercise.

The researchers found that there was no significant increase in preterm birth, defined as delivery before 37 weeks, in women who exercised than in those who did not. There were, however, a few benefits. Women who exercised were more likely to deliver vaginally -- 73 percent of exercising women delivered vaginally whereas 67 percent of non-exercising women delivered vaginally. Likewise, there was a lower incidence of C-section in women who exercised during pregnancy -- 17 percent of exercising women had a C-section versus 22 percent in those who did not. There was also lower incidence of gestational diabetes, and lower rates of high blood pressure in the exercising group.

All of the women included in this analysis were carrying a single baby (not twins), had normal weight to start with, and had no health conditions that prevented them from exercising.

"The results of this analysis support current guidelines from the American Congress of Obstetricians and Gynecologists (ACOG), which sets the recommendations for our field," says Dr. Berghella. "However, there are many reasons women pull back on exercise during pregnancy -- discomfort, an increase in tiredness and feeling winded by low level exertion. This paper reinforces that exercise is good for the mom and the baby and does not hold any increased risk preterm birth."