If you're nine months pregnant, you may be more than ready for labor to start and pregnancy to end. Exercise in pregnancy may have an effect on pregnancy duration and the length of labor, although there is no proof that lack of exercise will delay labor past the normal time. Some proof exists that women who exercise in pregnancy may deliver several days before women who don't exercise. Doctors often prescribe bed rest for women at risk for preterm labor, although there is no proof that it works.
Effects on Pregnancy Length
A study conducted by researchers from the University of Vermont College of Medicine and published in the December 1990 issue of the "American Journal of Obstetrics and Gynecology" found that 87 women who exercised on a regular basis in the second half of pregnancy delivered five to seven days earlier than 44 women who had previously exercised but stopped during the first trimester of pregnancy. Both groups of women delivered during the normal time range for pregnancy, at 36 weeks or later. However, an Australian study reported in the March 2002 issue of "Obstetrics and Gynecology" found that working women who exercised were more likely to need induction of labor and medication to speed up labor. The exercising women were also older, though, which has an effect on labor.
Effects on Labor Length
Women who exercised regularly had a shorter duration of labor, according to the University of Vermont Medical School researchers. The average labor length for exercisers was 264 minutes, plus or minus 149 minutes, while women who didn't exercise had an average active labor length of 38 minutes plus or minus 275 minutes if they had a vaginal delivery. But, the Australian study found the opposite -- that exercising women had longer labors and needed more medication to augment labor.
Preventing Preterm Delivery
If you're having contractions before 35 weeks, your doctor may put you on bed rest. Around 20 percent of pregnant women in the United States spend some time during the pregnancy on bed rest, according to BabyCenter. Bed rest can mean anything from normal activities with no additional exercise to complete confinement to the bed. Clinical studies on the effects of bed rest have not proved that bed rest helps to prevent preterm labor, although it may be necessary in cases of cervical incompetence, placental abruption or placenta previa or pre-eclampsia.
Most studies about exercise and labor are designed to test the effect of exercise, not the effect of lack of exercise in labor. Although exercise may cause labor to start a few days sooner, that doesn't mean that the lack of exercise delays labor. While a normal amount of exercise helps to keep you energized, improve your mood, sleep better and may enable you to get back into shape more quickly after delivery, it doesn't necessarily make pregnancy or labor easier or shorter.