Exercise During Pregnancy
A Critical Appraisal of The Literature
Stephanie N. Morris,M.D., and Natasha R. Johnson,M.D.
To Review the effects of exercise during pregnancy on fetal and maternal outcomes , a selective literature search was performed using MEDLINE , the Cochrane Database and bibliographies from relevant articles to identify additional references. The data on exercise during pregnancy are limited but suggest that moderate exercise during a low-risk pregnancy does not lead to adverse outcomes for the fetus or mother ant improves overall maternal fitness and well-being. The data examining the impact of exercise on labor outcomes, maternal weight gein and fetal weight are conflicting. Moderate exercise in the low-risk pregnancy improves maternal Well-being and does not seem to have adverse effects on the fetal or maternal outcome. However,further studies are needed. (J Reprod Med 2005;50:181-188)
Keywords:exercise,physical;pregnancy outcomes;pregnancy.
As the health benefits of exercise are increasingly recognized, more women are participating in regular physical activity. Approximately one-fourth of U.S. women participate in an exercise program;many want to continue during pregnancy. Although there are potential health benefits for women who exerxise during pregnancy , a major concern for both patients and providers is whethes exercise during pregnancy is associated with adverse fetal or maternal outcomes. The purpose of this article is to selectively review the clinically relevant literature examining the risks and benefits of exercise during pregnancy using an evidence-based approach.
The American College of Obstetricians and Gynecologists (ACOG) has revised its recommendations over the past 50 years, reflecting changing attitudes regarding exercise during pregnancy. In the 1950s, activity during pregnancy was limited to walking 1 mile per day , divided into multiple sessions, In 1985 ACOG suggested that 15-20 minutes of exercise limited to 3 days a week was safe in the uncomplicated pregnancy. By 1994 the recommendations were more open ended, stating that women could continue mild to moderate exercise if they had an already-established exercise program, A significant change occurred in 2002, when ACOG announced that moderate exercise 30 minutes or more per day , on most, if not all, day of the week,
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.
Was recommended for women with low-risk pregnancies. That bulletin also stated that previously sedentary women could start a new exercise program during pregnancy. These recommendations reiterate the most recent guidelines of the Centers for Disease Control and Prevention outlining the protective benefits of exercise in nonpregnant people
When evaluathing the literature, it is important to keep in mind that studies done on women who exercise during pregnancy were limited and problematic in several respective. First,although some studies were prospective,with large numbers of patients,most were observational,with only a few randomized trials. Second, not all exercise is the same; the type, intensity, duration and frequency of exercise differ between studies and are all important variables in determining the effects of exercise on the woman and her fetus. Furthermore, the control groups used in the studies are inconsisitent and range from women who have never exercised,to women who exercised before pregnancy but did not continue to exercised during pregnancy , to women who continued to exercise during pregnancy but to a lesser extent than the study population. This makes comparisons between studies challenging.
There are several sources of potential bias in the literature regarding exercise during pregnancy. Mose of the studies relied on self-reported exercise leadind to possible inaccuracy and reporting bias. Participation in these studies was voluntary;those who chose to participate in the study or to exercise during their pregnancy may have been inherently different from thrir nonexercising peers in several ways, including view on health, welless and dietary habits. This could lead to significant selection bias. In addition, the demographics of the women participating in these studies (mostly Caucisian women working outside the home , well educated and middle to upper socioeconomic class) make it difficult to generalize the results of these studies to the general population. Last, adverse out comes are rare, so large studies whit adequate power are needed to detect significant differences in outcomes. For these reasons, caution must be used when comparing results of different studies and when using study results to counsel individual patients.
Physiology of Exercise During Pregnancy
There are many Physiology changes During Pregnancy that affect the exercising gravida.
Beginning in the firse trimester of pregnancy,there is an increase in blood volume, plasma volume and red blood cell mass there is also is increase in cardiac output due to an increase in heart rate and stroke volume.5 There changes are seen as early as 5 weeks gestation, and by 12 weeks the rise in cardiac output is about 35% above pre- Pregnancy levels , accounting for 75% of the total increase in cardiac output seen during Pregnancy . Similar to normal Pregnancy cardiovascular changes, regular exercise also leads to an increase in cardiac output and blood wolume.6
The physiologic changer seen in women who exercise during pregnancy appear to be amplified. When comparing women who exercise before pregnancy , there is an additional 40% incardiac output in women who continue exercising in pregnancy when compared with women who do not. There is a similar effect seen with blood volume , which expands by an additional 20% in women who continue to exercise during pregnancy.