Maternal aerobic exercise during pregnancy may affect the experience of labor for the mother or fetus. Forty-four women who had given birth in the preceding 7 months responded to questions about their exercise habits during pregnancy. Using an exercise prescription formula, respondents were dichotomized into exercise or nonexercise groups. Maternal exercise was associated with a significant decrease in the duration of the second stage of labor (27 minutes vs 59 minutes, p = 0.04) and a reduction in the incidence of obstetric complications (8 vs 19, p = 0.058). The groups showed no significant differences in the number of weeks gestation, duration of the first or third stage of labor, birth weight, birth length, or neonatal Apgar scores at one and five minutes.