A randomized comparative trial of the efficacy and safety of exercise during pregnancy: Design and methods

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Abstract

Use of an exercise intervention for high-risk and vulnerable populations, such as pregnant women at risk for gestational hypertension or preeclampsia, requires special consideration. A comparative trial testing the effects of two types of physical exercises – stretching (a comparator) and walking (a testing intervention) – for sedentary pregnant women at risk for preeclampsia — is presented in this paper. The study was designed to reduce post-randomization bias and dropout rates from both groups, and closely to monitor safety of subjects. The strengths of the study design and methods include use of a run-in phase; use of a stretching exercise as a comparator; multiple ways to measure daily physical activities and the exercise intervention; and tailored support to remove barriers to exercise for subjects.

The intervention consists of 40 min of walking at moderate intensity (i.e., 55–69% of maximum heart rate and rating of perceived exhaustion 12–13) five times a week from 18 weeks gestation until birth. The comparator exercise consists of 40 min of stretching exercise without increasing heart rate to more than 10% of resting heart rate, five times a week from 18 weeks gestation until birth. The primary outcome is the incidence of preeclampsia. Secondary outcomes include the physiologic effects of the intervention and birth outcomes.

Introduction

Exercise studies can be grouped into two categories: single bout of exercise tests in laboratory settings (whether a test is repeated or not), and exercise intervention studies in communities. The first asks people to exercise at a certain intensity and duration in order to measure detailed physiological changes and sometimes psychological changes. The latter observes adherence to an exercise regimen and uses relatively rough measures of the intensity and duration of exercise. The goal of such studies often is to observe exercise-related behavior modification. When the goal of a study is to observe the effects of exercise on pregnancy outcomes at home, this approach needs to be modified because gestational length may influence exercise effects. More detailed monitoring of the safety of exercise is also needed in pregnancy. Thus exercise interventions for high-risk pregnancies require special considerations. Currently the author and her research team are conducting a randomized comparative trial examining the effect of regular exercise among pregnant women at risk for preeclampsia.

A disorder of human pregnancy in which the normal hemodynamic response to pregnancy is compromised, preeclampsia is a leading cause of maternal morbidity (2–10% of all pregnancies) and mortality and is associated with a significant increase in perinatal mortality [1], [2], [3], [4]. A woman who experienced preeclampsia in a previous pregnancy is 1.6 times more likely to develop preeclampsia again than a woman without such history [5]. Preeclampsia is diagnosed primarily by the onset of hypertension and proteinuria in the latter half of gestation. Other manifestations of preeclampsia include generalized vasoconstriction, increased vasoactivity, reduced perfusion to organs, and platelet activation [6], [7]. Both the etiology and pathophysiology of preeclampsia are poorly understood. Currently, there are no conclusive preventive treatments available.

The purposes are to determine whether moderate intensity exercise during pregnancy reduces the incidence of preeclampsia and to assess the process (involving oxidative stress and the antioxidant process) hypothesized to explain the relationship between the effect of exercise and pathophysiologic progress of preeclampsia.

Section snippets

Aims

The following specific aims guided the trial design:

  • 1.

    To determine whether regular exercise during pregnancy reduces the incidence of preeclampsia.

  • 2.

    To determine whether regular exercise enhances the antioxidant process and reduces susceptibility to oxidative stress among pregnant women.

  • 3.

    To assess the associations among antioxidant activity, lipid peroxidation, and susceptibility to oxidative stress.

  • 4.

    To determine whether anioxidant activity and susceptibility to oxidative stress at various points in

Methods and design

This randomized trial compares moderate intensity exercise, repeated regularly during pregnancy, to a traditionally recommended maternal stretching exercise in women who have developed preeclampsia in a previous pregnancy and thus at high risk. Fig. 1 shows the overall design. Subjects are recruited before 14 weeks gestation, followed by a run-in period of 4 weeks. Those who succeed in scheduled weekly visits in the run-in phase are randomized to walking or stretching exercise. Both groups

Preliminary results

As of March 2006, 322 pregnant women had been referred by nurses at prenatal clinics or by themselves (Fig. 2). Of the 322 potential subjects, 217 (67%) were excluded for one reason or another, 11 are pending, 94 (29%) never communicated other than at the clinics, and 94 (29%) were randomized. Of the 217 women excluded, 191 (88%) did not get as far as consent. Seventy-two percent of them refused to participate and the rest appeared ineligible. Twenty-six women consented but left before being

Discussion

Use of regular exercise, walking in this case, as a preventive intervention for high-risk pregnant women is a new idea and it therefore required careful assessment of effectiveness and safety in our design. The design embodies a 4-week run-in period prior to randomization, a stretching exercise as the comparator, and the use of subjective and objective measures of daily physical activities throughout pregnancy. Additionally, interventions are tailored to individual supports based on

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  • Cited by (17)

    • Associations between maternal physical activity and fitness during pregnancy and infant birthweight

      2018, Preventive Medicine Reports
      Citation Excerpt :

      All participants wore Polar S810 heart rate monitors and wristwatch devices to validate their adherence to the walking or stretching programs. Further details on the intervention and comparative groups can be found elsewhere (Yeo, 2006). For the purposes of this study, the data were collapsed across both groups and group allocation was controlled for in the analyses.

    • Diagnosis, evaluation, and management of the hypertensive disorders of pregnancy

      2014, Pregnancy Hypertension
      Citation Excerpt :

      Among sedentary women with prior preeclampsia specifically, walking vs. stretching exercise did not alter pregnancy outcomes [276]. There is one ongoing RCT of moderate intensity exercise in women with prior preeclampsia [277]. RCT evidence is lacking for workload or stress reduction to prevent preeclampsia.

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