In the comparative obstetric mobile epidural trial (COMET), the rate of instrumental vaginal delivery (IVD) was reduced among nulliparous women with 2 mobile epidural analgesic techniques, combined spinal epidural (CSE) or low-dose infusion (LDI), in comparison with the high-dose epidural technique. There was no loss of efficacy in pain relief with either mobile procedure. It is unclear whether maternal ambulation (women walking or adopting upright postures) during labor is causally related to a reduction in IVD or an increased likelihood of spontaneous vaginal delivery. The few randomized controlled trials have examined the effect of continuous epidural pain relief on maternal mobility in labor and not necessarily on labor outcome. This randomized trial investigated the effect of 2 mobile epidural techniques, CSE and LDI, on maternal motor power and ambulation as a predefined secondary outcome of the COMET trial in nulliparous women during labor. The 1054 study subjects were randomly allocated to 1 of 3 groups. The control group (n = 353) received high-dose epidural analgesia and was compared with the CSE group (n = 351) and the LDI group (n = 350). The mode of delivery (spontaneous vaginal delivery, IVD, or cesarean section) was the predefined study outcome. To determine the level of ambulation achieved by the study subjects after epidural insertion during first and second stages of labor, motor function was assessed hourly using modified Breen's Bromage power scores, until delivery.
Compared to the control group, normal leg power was maintained throughout labor in significantly more women in the CSA and LDI groups (P < 0.01 for each hour). A greater proportion of women in the CSA group than in the LDI group maintained normal leg power during labor (P < 0.01 for each hour). However, there was no association between the level of ambulation and the delivery method. These findings do not support the assertion that a greater level of ambulation after epidural insertion during labor has a beneficial effect on the mode of delivery.