Increased Aerobic Fitness In Late Pregnancy Predicts Shorter Labor In Nulliparous, But Not Multiparous, Women.

Abstract

Similar to the general population, the level of physical activity is inadequate among pregnant women. The ensuing state of over-nutrition as a consequence of physical inactivity prolongs labor and thereby the risk of several obstetrical implications including fetal asphyxia, infections and obstetrical fistulas. Well-trained women who maintain physical exercise during pregnancy have shorter labor compared to those who stop training before the end of the first trimester. Much less is known about whether aerobic fitness in a general cohort of pregnant women is related to duration of labor. PURPOSE: We wanted to investigate the effect of aerobic fitness on duration of labor among nulli- and multiparous women using two valid indicators, namely measurement of maximal oxygen uptake and calculation of anaerobic threshold. METHODS: Maximal oxygen uptake and anaerobic threshold were measured in 59 nulli- and 51 multiparous women at 36 weeks of gestation. Duration of labor was defined as the time between three cm cervical dilation with regular uterine contractions and delivery. Unpaired sample t-test, Pearson correlation test and multiple linear regression were used for statistical analysis. RESULTS: Maximal oxygen uptake was similar for both groups (mean 2.1 L/min). Labor was as expected longer (p < 0.001) in the nulliparous compared to the multiparous women: 9.3±5.0 and 4.5±2.3 hours, respectively. For nulliparous women who started labor spontaneously, duration of labor was inversely associated with maximal oxygen uptake (p=0.03). This indicates that for an increase in maximal oxygen uptake of 0.1 L/min, labor would be shortened by on average 33 minutes. In contrast, in multiparous women who started labor spontaneously, anaerobic threshold was positively associated with duration of labor (p=0.002). This indicates that an increase in anaerobic threshold of 0.1 L/min would prolong labor by on average 22 minutes. Conclusion: Increased maximal oxygen uptake is associated with shorter labor in nulliparous women who start labor spontaneously, whereas increased anaerobic threshold is associated with prolonged labor in multiparous women.