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 to the general population. Certainly more 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.