COMMENTARY

Exercise, Pregnancy, and Preterm Birth: What Advice Can We Give?

Peter Kovacs, MD, PhD

Disclosures

February 27, 2018

Exercise and Risk for Preterm Birth

Preterm birth is a major risk factor for neonatal mortality and morbidity, as well as childhood cognitive impairment and chronic diseases.[1,2] The known risk factors for preterm birth include previous preterm birth, multifetal gestation, uterine anomalies, medical problems, smoking, and high body mass index (BMI).[3]

Obesity is prevalent in the reproductive-aged population. Ideally, obesity should be addressed before pregnancy to increase the chance of successful conception and to reduce the risk for prenatal medical complications. Gestational diabetes, hypertensive complications, thromboembolism, and operative deliveries are more common among obese or overweight women.

Lifestyle changes (eg, improved diet, initiation of regular physical activity) are considered the first-line intervention for those with high BMIs. A reasonable diet and exercise program can also be continued during pregnancy. However, the association between physical activity and preterm birth has been studied by many, with conflicting results.[4] A recent systematic review[5] combined the data from cohort studies and randomized controlled trials (RCTs) to determine whether there is a link between physical activity and preterm birth.

Findings

A total of 41 studies (21 cohort studies and 20 RCTs) were included in the analysis. Key findings included the following:

  • The relative risk (RR) for preterm birth was 0.87 (95% confidence interval [CI], 0.7-1.06) with high versus low prepregnancy leisure-time activity.

  • The RR for preterm birth was 0.86 (95% CI, 0.78-0.95) with high versus low physical activity during pregnancy. In the cohort studies, the RR was 0.84 (95% CI, 0.73-0.96), whereas in the RCTs it was 0.91 (95% CI, 0.72-1.15).

  • The RR for preterm birth was 0.46 (95% CI, 0.22-1.83) with high versus low moderate physical activity and was 0.36 (95% CI, 0.04-3.09) for vigorous activity during pregnancy.

  • The RR for preterm birth with high versus low occupational physical activity was 0.67 (95% CI, 0.33-1.34), whereas it was 0.95 (95% CI, 0.63-1.42) for high versus low combined (occupational and leisure-time) activity.

The reviewers concluded that higher physical activity during pregnancy was associated with lower risk for preterm birth, and these findings support remaining active during gestation.

Viewpoint

Obesity is a risk factor not only for preterm delivery, but also for medical complications during pregnancy. Consuming a well-balanced, appropriate-calorie diet combined with regular physical exercise is an effective way to control weight. During pregnancy, many women are concerned that maintaining regular physical activity is associated with preterm delivery, and they therefore give up exercise. This may lead to more rapid weight gain and higher risk for diabetes or hypertensive complications.

Aune and colleagues[5] found that prepregnancy exercise is not associated with an increased risk for preterm delivery and that exercise during pregnancy is associated with a lower risk. In a dose/response analysis, they found that each extra 3 hours of exercise lowers the risk by 10%. Obviously, there are conditions in which exercise (especially vigorous) is not advised; these include bleeding, multifetal pregnancy, and immediate risk for preterm delivery owing to cervical shortening or rupture of membranes. However, most pregnant women can carry on exercising.

Women who exercise regularly may follow a healthier diet, be less likely to smoke, and be exposed to less stress overall. Women who are active before pregnancy may also differ from those who start to exercise during pregnancy. These differences could affect their overall risk for preterm delivery. And other confounding factors may be responsible for the observed differences. In RCTs, however, confounding factors should be equally present in all groups, and cohort studies tried to control for these factors.

The optimal duration and intensity of physical activity during pregnancy remain to be determined. Are different types of activity equally harmless, and do some activities carry risks? For now, on the basis of these findings, we can reassure pregnant women that by staying active, they do not compromise the outcome of their pregnancy.

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