Conclusion
The disparate results found in many of the studies examining the effects of exercise during pregnancy could be based on several factors. First, not all exercise is the same, and different types of exercise, intensity and duration may have different impacts on pregnancy. In addition, the highly variable definitions of exercise make comparisons between studies, exposures and results challenging. Furthermore, the women who participate in the studies are volunteers, leading to potential selection bias. The women who chose to exercise and continued exercise through pregnancy may have been inherently different from their nonexercising peers in several ways, including views on health, dietary habits, body composition and preferences about anesthesia during labor. The women who exercised may also have been more athletically inclined, making it difficult to distinguish the effects of exercise vs. physical fitness on pregnancy outcomes. The women in these studies were generally Caucasian, middle to upper class and worked outside the home. All these factors make it difficult to apply the results of the studies are needed to refine our understanding of the effects of exercise during pregnancy, to examine exercise during pregnancy in different patient populations and to elucidate the long-term outcomes for both mother and infant.
A few general conclusions can be made from the literature. From the available evidence, moderate exercise in the low-risk pregnancy appears to be safe for both the fetus and mother. There are several physiologic factors that may be protective for women who exercise during pregnancy. Although there is decreased uterine blood flow during strenuous exercise, there appears to be compensatory mechanisms, such as preferential shift of blood flow to the placenta and increased oxygen extraction. Maternal conditioning may lessen the exercise induced decrease in uterine blood flow. Also, thermoregulatory adaptations appear in early pregnancy, may confer a protective effect during fetal development and may limit thermal stress in women who continue to exercise throughout pregnancy.
The data regarding maternal and fetal outcomes is quite varied. In the low-risk pregnancy there are no apparent adverse pregnancy outcomes associated with moderate exercise-no increased risk of miscarriage, preterm labor, preterm birth or intrauterine growth restriction. There is no consistent effect on fetal weight . Exercise has been shown to improve maternal fitness and well-being but does not have a clear effect on maternal weight gain or labor outcomes.