Expectant mothers can reduce the likelihood that they will gain too much weight during pregnancy by improving their diet, increasing their exercise, or using a combined diet and exercise program, according to an updated Cochrane review.

The original review published in 2012 found too little evidence to conclude that diet and exercise interventions could benefit pregnant women and their newborns, but the update includes an additional 41 randomized controlled studies published between October 2011 and November 2014, along with 24 studies from the original review.

“Moderate-intensity exercise appears to be an important part of controlling weight gain in pregnancy; however, the evidence on the risk of preterm birth is limited, and more research is needed to establish safe guidelines,” wrote Benja Muktabhant of Khon Kaen (Thailand) University and associates (Cochrane Database Syst. Rev. 2015 June 10 [ doi:10.1002/14651858.CD007145.pub3 ]).

Excessive weight gain in pregnancy is well known to increase the risk for poor maternal and neonatal outcomes, including gestational diabetes, hypertension, cesarean delivery, macrosomia, and stillbirth. But research shows that pregnant women continue to struggle to stay within recommended weight limits. In 2009, the Institute of Medicine (IOM) recommended that normal weight women with singleton pregnancies gain 25-35 pounds, while overweight women should gain 15-25 pounds. For obese women with a body mass index of 30 kg/m2 or greater, the IOM recommendation is 11-20 pounds of weight gain.

In the current review, the researchers identified a total of 65 randomized controlled trials that focused on using exercise, diet, or both to prevent excessive gestational weight gain. The 49 studies that were part of the quantitative meta-analysis included 11,444 women, but the methodologies varied greatly among the studies, and 20 studies had a moderate to high risk of bias. Further, the majority of studies included participants from high-income countries, primarily the United States, Canada, Australia, and European countries, making generalization to lower-income populations difficult to assess.

Using diet, exercise, or both reduced the risk of excessive weight gain in pregnancy by 20% based on 24 studies involving 7,096 participants. This evidence, rated high quality, found that low-glycemic-load diets, exercise with and without supervision, and combined diet and exercise programs all reduced women’s weights by similar amounts. Diet and/or exercise programs also increased the likelihood by 14% that women would have a low gestational weight gain, based on 4,422 participants in 11 studies with moderate-quality evidence.

Exercise programs included moderate exercise such as walking, dance, or aerobics.

The risk of maternal hypertension was lower in the diet and/or exercise intervention groups based on 11 studies involving 5,162 participants, but the researchers graded the evidence as low quality because of inconsistency and risk of bias concerns. The researchers found no reduced risk for preeclampsia in the 15 studies that included it as an outcome.

Similarly, the 16 studies assessing preterm birth and the 28 studies assessing risk of cesarean delivery found no difference between the intervention and control groups. However, when the researchers looked only at a combined diet and exercise intervention, they found a 13% reduction in cesarean delivery, which had borderline statistical significance.

The potential risk reduction of infant macrosomia depended on a woman’s prepregnancy weight, with only the findings for overweight or obese women, or those with or at risk for gestational diabetes, barely reaching statistical significance. Among the 27 studies with 8,598 participants that included macrosomia as an outcome, the 7% lower risk for oversized newborns just missed statistical significance. Among high-risk women, combined diet and exercise counseling reduced macrosomia risk by 15% (P = .05) with moderate-quality evidence from 3,252 participants in nine studies.

There was no difference between the two groups in risk for shoulder dystocia, neonatal hypoglycemia, hyperbilirubinemia, and birth trauma, according to the review.

The project was supported by the National Institute for Health Research in the United Kingdom, and the World Health Organization. The researchers reported having no relevant financial conflicts.