Background
Preterm birth is the major cause of perinatal mortality in the United States. In the
past, pregnant women have been recommended to not exercise because of presumed risks
of preterm birth. Physical activity has been theoretically related to preterm birth
because it increases the release of catecholamines, especially norepinephrine, which
might stimulate myometrial activity. Conversely, exercise may reduce the risk of preterm
birth by other mechanisms such as decreased oxidative stress or improved placenta
vascularization. Therefore, the safety of exercise regarding preterm birth and its
effects on gestational age at delivery remain controversial.
Objective
The objective of the study was to evaluate the effects of exercise during pregnancy
on the risk of preterm birth.
Data Sources
MEDLINE, EMBASE, Web of Sciences, Scopus, ClinicalTrial.gov, OVID, and Cochrane Library were searched from the inception of each database to
April 2016.
Study Design
Selection criteria included only randomized clinical trials of pregnant women randomized
before 23 weeks to an aerobic exercise regimen or not. Types of participants included
women of normal weight with uncomplicated, singleton pregnancies without any obstetric
contraindication to physical activity. The summary measures were reported as relative
risk or as mean difference with 95% confidence intervals. The primary outcome was
the incidence of preterm birth <37 weeks.
Tabulation, Integration, and Results
Of the 2059 women included in the meta-analysis, 1022 (49.6%) were randomized to the
exercise group and 1037 (50.4%) to the control group. Aerobic exercise lasted about
35–90 minutes 3–4 times per week. Women who were randomized to aerobic exercise had
a similar incidence of preterm birth of <37 weeks (4.5% vs 4.4%; relative risk, 1.01,
95% confidence interval, 0.68–1.50) and a similar mean gestational age at delivery
(mean difference, 0.05 week, 95% confidence interval, –0.07 to 0.17) compared with
controls. Women in the exercise group had a significantly higher incidence of vaginal
delivery (73.6% vs 67.5%; relative risk, 1.09, 95% confidence interval, 1.04–1.15)
and a significantly lower incidence of cesarean delivery (17.9% vs 22%; relative risk,
0.82, 95% confidence interval, 0.69–0.97) compared with controls. The incidence of
operative vaginal delivery (12.9% vs 16.5%; relative risk, 0.78, 95% confidence interval,
0.61–1.01) was similar in both groups. Women in the exercise group had a significantly
lower incidence of gestational diabetes mellitus (2.9% vs 5.6%; relative risk, 0.51,
95% confidence interval, 0.31-0.82) and a significantly lower incidence of hypertensive
disorders (1.0% vs 5.6%; relative risk, 0.21, 95% confidence interval, 0.09-0.45)
compared with controls. No differences in low birthweight (5.2% vs 4.7%; relative
risk, 1.11, 95% confidence interval, 0.72–1.73) and mean birthweight (mean difference,
–10.46 g, 95% confidence interval, –47.10 to 26.21) between the exercise group and
controls were found.
Conclusion
Aerobic exercise for 35–90 minutes 3–4 times per week during pregnancy can be safely
performed by normal-weight women with singleton, uncomplicated gestations because
this is not associated with an increased risk of preterm birth or with a reduction
in mean gestational age at delivery. Exercise was associated with a significantly
higher incidence of vaginal delivery and a significantly lower incidence of cesarean
delivery, with a significantly lower incidence of gestational diabetes mellitus and
hypertensive disorders and therefore should be encouraged.
Key words
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Article info
Publication history
Published online: June 16, 2016
Accepted:
June 7,
2016
Received in revised form:
June 1,
2016
Received:
May 9,
2016
Footnotes
The authors report no conflict of interest.
Identification
Copyright
© 2016 Published by Elsevier Inc.
