Benefits from exercise during pregnancy

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Women who exercise during pregnancy are less likely to have a C-section and have no greater risk of preterm birth, found a Thomas Jefferson University meta-analysis.

Researchers collected and re-examined clinical trial data on exercise during pregnancy and whether it plays a role in preterm birth, and found that exercise is safe and does not increase the risk of preterm birth. In addition, women who exercised were less likely to have a C-section than those who did not.

Historically, women were discouraged from vigorous exercise during pregnancy because of the risk of preterm birth. “The thinking was that exercise releases norepinephrine in the body, which is a chemical that can stimulate contractions of the uterus, and thus lead to preterm birth,” says senior author on the study Dr Vincenzo Berghella, director of maternal foetal medicine and professor at the Sidney Kimmel Medical College at Thomas Jefferson University. “But numerous studies including this new meta-analysis, have since shown that exercise does not harm the baby, and can have benefits for the mom and baby.”

Berghella and his co-authors pooled data from nine randomised controlled studies – one of the strongest types studies involving human subjects – in which pregnant women were divided into two groups. Of the 2,059 women who were included in the analysis, about half (1,022 women) exercised for 35-90 minutes 3-4 times per week for 10 weeks or up until their delivery, whereas the other half, (1,037 women) engaged in no exercise.

The researchers found that there was no significant increase in preterm birth, defined as delivery before 37 weeks, in women who exercised than in those who did not. There were, however, a few benefits. Women who exercised were more likely to deliver vaginally – 73% of exercising women delivered vaginally whereas 67% of non-exercising women delivered vaginally. Likewise, there was a lower incidence of C-section in women who exercised during pregnancy – 17% of exercising women had a C-section versus 22% in those who did not. There was also lower incidence of gestational diabetes and lower rates of high blood pressure in the exercising group.

All of the women included in this analysis were carrying a single baby (not twins), had normal weight to start with, and had no health conditions that prevented them from exercising.

“The results of this analysis support current guidelines from the American Congress of Obstetricians and Gynaecologists (ACOG), which sets the recommendations for our field,” says Berghella. “However, there are many reasons women pull back on exercise during pregnancy – discomfort, an increase in tiredness and feeling winded by low level exertion. This paper reinforces that exercise is good for the mom and the baby and does not hold any increased risk preterm birth.”.

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 mainly 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 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 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.

Daniele Di Mascio, Elena Rita Magro-Malosso, Gabriele Saccone, Gregary D Marhefka, Vincenzo Berghella

Thomas Jefferson University material
American Journal of Obstetrics & Gynaecology abstract

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