Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.
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.


METHODS
MEDLINE, EMBASE, Web of Sciences, Scopus, ClinicalTrial.gov, OVID, and Cochrane Library were searched from the inception of each database to April 2016.


METHODS
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.


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.


CONCLUSIONS
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.
School of Medicine and Health Sciences, D'Annunzio University of Chieti-Pescara, Chieti, Italy.
Daniele
D
Di Mascio
Department of Health Science, Division of Pediatrics, Obstetrics, and Gynecology, Careggi Hospital University of Florence, Florence, Italy.
Elena Rita
ER
Magro-Malosso
Department of Neuroscience, Reproductive Sciences, and Dentistry, School of Medicine, University of Naples Federico II, Naples, Italy.
Gabriele
G
Saccone
Division of Cardiology, Department of Medicine, Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia, PA.
Gregary D
GD
Marhefka
Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia, PA. Electronic address: vincenzo.berghella@jefferson.edu.
Vincenzo
V
Berghella
D002585:Cesarean Section / Q000706:statistics & numerical data*; D036861:Delivery, Obstetric; D016640:Diabetes, Gestational / Q000453:epidemiology; D015444:Exercise; D005260:Female; D005865:Gestational Age; D006801:Humans; D046110:Hypertension, Pregnancy-Induced / Q000453:epidemiology; D015994:Incidence; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012306:Risk
exercise during pregnancy; obstetric outcomes; physical activity; pregnancy outcomes; preterm birth; preterm delivery