The current study found that there was no effect on the cardiovascular capacity of the women or on the duration of labor or the type of delivery for women practicing water aerobics regularly during pregnancy in comparison to those not practicing exercise at all. However, fewer women in the exercise group requested analgesia.
Most of the knowledge available today on the practice of physical exercise during pregnancy is based on longitudinal and, mainly, observational studies. This randomized controlled trial may contribute towards greater comprehension of the interaction between pregnancy and the practice of water aerobics, as well as the repercussions of exercise in labor and on the well-being of the newborn infant.
Cardiovascular parameters of VO2
max, cardiac output and submaximal endurance heart rate showed similar results in both groups, showing that the practice of water aerobics according to the regimen described in this study failed to have any effect on physical capacity. These results are in agreement with data published by Prevedel et al. [6
max and physical capacity (MET) increased during the second trimester of pregnancy and returned to previous values during the third for both groups, while Wolfe et al [12
] reported an increase in VO2
max with the progression of pregnancy in women who participated in a program of physical conditioning, while values remained unchanged in a group of sedentary pregnant women, but evaluations were made using ergometric bicycles. Santos et al. [13
] reported a substantially increase in submaximal exercise capacity in overweight pregnant women who were submitted to aerobic exercise sessions also in a randomized controlled trial.
The increase in resting heart rate over the course of pregnancy was an expected result and may be explained by a reduction in vagal parasympathetic control. The smaller increase in heart rate during exercise in the third trimester of pregnancy may be a result of the reduction in the response to sympathetic stimulation during pregnancy [14
The maintenance or reduction of systolic blood pressure in the second trimester and reduction of diastolic blood pressure confirm that the response of arterial blood pressure during pregnancy is related to a reduction in peripheral vascular resistance [16
]. At the second evaluation, the lower value of diastolic blood pressure during exercise may be a result of the lower response to sympathetic stimulation. The expected effect of vascular pumping caused by the balance between vasoconstriction of the non-active musculature versus vasodilatation of the active musculature may not be sufficiently adapted to overcome the present reduction in peripheral vascular resistance. This preloading reduction may consequently lead to a post-loading reduction and lower systolic blood pressure, which was probably compensated by an increase in the ventricular contractility during exercise at the beginning of pregnancy [18
]. The rise in systolic blood pressure during exercise in the third trimester showed an adequate adjustment in the pressure-volume curve at acute endurance.
These results show that the pregnant women had an adequate adaptive response to the demands of a normal pregnancy. Moreover, they were capable of compensating for greater demands such as an endurance test or the practice of regular, moderate physical activity in water despite the fact that no effect was obtained on cardiovascular conditioning during pregnancy.
The reduction in fetal heart rate with the progression of pregnancy may be directly related to the immaturity, particularly parasympathetic immaturity, of the autonomous fetal nervous system in the first half of pregnancy. The increase in FRH observed during recovery may be explained by the liberation of maternal catecholamines during physical exercise, confirmed by the increase in maternal HR [20
]. However, in the third trimester, the group that practiced water aerobics appeared to show a more adequate autonomic response than the control group. Probably this response accompanies the reduction in the maternal response to sympathetic stimulation during this period of pregnancy [15
Van Doorn et al. [21
] described an increase in FHR five minutes after maternal peak exercise. Veille et al. [22
]) reported no change in FHR during 30 minutes following moderate maternal exercise. Carpenter et al. [23
] also failed to find any significant differences in FHR at rest and 5 minutes following maternal peak exercise.
To avoid possible side effects of maternal-fetal hyperthermia, endurance tests were always carried out at the same time of the day, in the same environmental conditions and in a cool, well-ventilated room, in order to minimize the increase in skin temperature of the volunteers. The acceptable maternal skin temperature of approximately 38.9°C was respected [24
Maternal temperature increased in response to strenuous exercise and remained high in both groups until 15 minutes following the end of exercise, causing no ill effects to fetal vitality as can be seen from the response in FHR. These results are in agreement with data published by Soultanakis-Aligianni [24
] who described an increase in maternal temperature during exercise of approximately 0.7°C and 0.4°C at 20 and 32 weeks of pregnancy, respectively. This increase found in skin temperature was lower for the cases studied by Larson & Lindqvist [25
] and Lindqvist et al.[26
] and one possible explanation refers to the fact that these authors measured the core temperature instead skin temperature. The difference between skin and core temperature might be interpreted as a safety mechanism during pregnancy exercise. This would give a possible explanation to the trend towards increased skin temperature in the exercise group.
Some limitations of the current study could be pointed out. Probably the most important refers to the practical difficulty of maintaining a high compliance with the water aerobics program. Although these women had free access to the swimming pool and professional oriented sessions of water aerobics, plus the costs for transport three times per week, around one third of them discontinued the program during pregnancy due to logistic and family constraints, including job restrictions, care of children and home affairs.
The results of this study show that the regular practice of moderate water aerobics during pregnancy by low risk women who were previously sedentary is not detrimental to the health of the mother or the child. Although there was no effect on the cardiovascular capacity of the expectant mothers, on the duration of labor or the type of delivery, fewer women in the water aerobics group requested analgesia, probably because of better psycho-physical condition. Clap III [27
], who studied women that practiced physical activity and who either continued or spontaneously stopped exercising (control group) in the first trimester of pregnancy, observed similar results. This author observed a lower incidence of Cesarean sections, shorter duration of labor, a greater number of vaginal deliveries, and less need for epidural anesthesia among women who continued exercising during pregnancy. Moreover, infants born to women in the exercise group were smaller and had higher Apgar scores at the first minute.
Neonatal results from this present study confirm the wellbeing of the newborn infants born to mothers who initiated regular physical activity in water during pregnancy. Therefore this kind of exercise could be recommended to mothers willing to practice any physical activity during pregnancy [27
]. The babies had adequate weight, gestational age and vitality at birth, confirming the trend that already exists in the literature that moderate, regular physical activity has no influence on prematurity or on the weight of the newborn infant. However, the adequacy of the exercise has to be assured since the practice of physical activity that is rigorous either in its intensity, duration or frequency is associated with low neonatal birthweight [5