The Effects of Aerobic Water Exercise on Pregnancy

INTRODUCTION

Significant hemodynamic changes take place during the short period of pregnancy, very often placing a major burden on the maternal cardiovascular system. Normal pregnancy is characterized by an increase in cardiac output (CO), stroke volume (SV), heart rate (HR) and blood volume, and decrease in arterial pressure and vascular resistance. Classic studies have demonstrated an increase of up to 50% in maternal CO during the second and third trimesters. These circulatory adaptations are responsible for supplying nutrients and oxygen to the placenta and the fetus.

The physiological changes that follow regular exercise improve training efficiency and performance, defining the concept of adaptation to exercise or aerobic training. Exercise causes the heart and lungs to be more efficient by increasing cardiovascular capacity or resistance. CO, SV and maximum oxygen consumption (VO2max) increase while HR and AP decrease. The importance of these effects on overall health has been recognized by the most outstanding medical and scientific groups. Therefore, regular exercise has been widely promoted and a large number of women decide to begin or continue to exercise during pregnancy.

This change in women's behavior has become a matter of concern among obstetricians and has important practical implications - is the maternal body apt to bear the hemodynamic burden of pregnancy in association with exercise stress? Studies on the effects of exercise on pregnancy are scarce and show conflicting results, probably due to differences in exercise frequency, intensity, type, duration, and gestational age at training initiation.

Aiming at standardizing exercise practice and thus promote materno-fetal health, the American College of Obstetricians and Gynecologists (ACOG) issued, in 1985, guidelines for exercise during pregnancy. In subsequent reviews, new recommendations were added, and water exercise during pregnancy was recommended.

Water exercise offers some particular benefits that include the maintenance of body temperature, control of gestational edema, and increase in diuresis. Moreover, it can be easily performed up to the end of pregnancy, which favors compliance. These advantages added to the fact that it has no adverse effect on the fetus explain the preference for this kind of exercise during pregnancy.

Considering the lack of scientific evidence of the effects of exercise during pregnancy, and the results obtained in our previous work, the purpose of this study was to assess the relationship of aerobic water exercise during the gestational periods of greater hemodynamic burden with maternal cardiovascular capacity and neonatal outcomes.

METHODS

This study is part of a project approved by the Committee of Research Ethics of the Botucatu Medical School-UNESP on May 10, 1999.

Study design: randomized clinical, without intention to treat. Study subjects: All the eligible women who volunteered to participate were sequentially enrolled and randomized to one of two groups according to a computer-generated randomization list of numbers created with Epi-Info software. Each sequential number corresponded to a sealed opaque envelope containing the information on the randomization group in order to ensure concealment. Group 1 consisted of 29 women engaged in Water Exercise, and group 2 included 31 pregnant women not participating in the program (control). Variables: the independent variable studied was the practice of water exercise. The control variables, which were assessed at baseline, included age, parity, pre-gestational body mass index (BMI), HR and MAP, smoking, sedentarism, and gestational age at baseline and at stress testing. The dependent variables regarding cardiovascular capacity and physical performance at the submaximal stress test were VO2max; SV; CO; HR and MAP, relative HR treadmill speed and scores obtained with the scale of Borg. Neonatal variables included gestational age, weight; Apgar index at minute 1 and at minute 5, and length (days) of infant's hospitalization.

Assessment of cardiovascular capacity: performed during prenatal visits at 16-20, 28-33 and 34-39 weeks. Cardiovascular capacity was evaluated by using a treadmill submaximal stress test, according to the protocol of Balke-Ware \& Bruce that requires five minutes on treadmill at fixed incline and constant individualized speed with AP and HR monitoring. Assessment of physical performance at stress testing - for this purpose, relative HR, treadmill speed and the Borg scale scores, obtained during testing, were used. A specific questionnaire was administered to all subjects in order to quantify stress perception during testing.

Data processing and analyses - given that the aim of this study was to assess the efficacy (exploratory and not intention-to-treat) of water exercise during pregnancy, our analysis included only the subjects who underwent cardiovascular assessment at the three study moments and missed no more than 2 exercise sessions/month. These data were stored in a specific database Statistical analysis was performed with SPSS software version 10.0.7. Means were compared using ANOVA followed by t-tests for independent (between groups) and dependent (within groups) samples. Data were adequately transformed when necessary. Proportions were compared by the chi-square test (X2). Statistical significance was set at 5% (p<0.005).