#Grand Rounds

Does Physical Activity During Pregnancy Reduce Risk for Preterm Birth?

BACKGROUND AND PURPOSE:

Data is inconsistent regarding physical activity and risk of preterm birth and may be limited due to small sample size
Aune et al. (BJOG, 2017) sought to elucidate the link between physical activity and risk of preterm birth
Of particular interest was ‘dose-response’ and comparing total, leisure-time an occupational physical activity

Systematic review and dose-response meta-analysis
Studies were prospective cohort, case-cohort, nested case-control (within a cohort) or randomized study design
Data was extracted by one reviewer and checked by a second
Preterm defined as <37 weeks and was consistent across studies

20 randomized trials and 21 cohort studies were included
When comparing leisure-time high versus low activity
- Physical activity before pregnancy: Non-significant relative risk (RR) 0.87 (95% CI, 0.70–1.06)
- Early pregnancy physical activity: Significant RR 0.86 (95% CI, 0.78–0.95)
The summary RR for increment in leisure-time activity was
- 0.90 (95% CI, 0.85–0.95) for a 3 hour increment
- 0.84 (95% CI, 0.76-0.91) for a 5 hour increment
Total physical activity (leisure-time plus occupational) during pregnancy
- No significant association
Occupational physical activity during pregnancy
- No significant association
Walking during pregnancy
- No significant association
Bicycling during pregnancy
- No significant association
There was a nonlinear association between physical activity and preterm birth (P_nonlinearity< 0.0001), with the lowest risk observed at 2–4 hours (15-16% reduction) per week of activity but no additional benefit after that amount of time per week
- Limited data points at higher levels of activity
- Previous studies have documented benefit up to 5-7 hours per week in reducing risk for preeclampsia, gestational diabetes and type 2 diabetes

Higher leisure-time physical activity during pregnancy was associated with a 14% decrease in RR of preterm birth
A 3-hour per week increase in leisure-time physical activity during pregnancy reduced risk by a 10% for preterm birth
Leisure-time physical activity before pregnancy, and total, moderate or vigorous physical activity (including bicycling, walking and occupational physical activity) during pregnancy, were not significantly associated with reduced risk for preterm birth, but likely due to small sample size
While further studies are needed, authors suggest that these results should reinforce recommendations for women to stay active during pregnancy on most if not all days of the week

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