Type of axial analgesia does not influence time to vaginal delivery in a Proportional Hazards Model

Objective To create a Proportional Hazards Model of prospective factors associated with time-to-vaginal-delivery (TTVD). Methods We analyzed a group of 144 women undergoing childbirth who received one out of two possible axial analgesia techniques, to find-out factors associated with TTVD. The patients were randomly assigned to receive either a levobupivacaine labor epidural (bolus concentration 0.25 % or less; infusion concentration 0.125 % or less) or a combined spinal–epidural procedure (morphine 0.20 mg, fentanyl 25 µg and hyperbaric bupivacaine 2.5 mg as spinal components) for labor analgesia. The factors initially chosen were: mother age, height and weight, parity, gestational age, newborn weight, type of labor, analgesic procedure, levobupivacaine and fentanyl doses, Bromage scale, pain Numeric Rating Scale, and a satisfaction interview. Cesarean section was the censored variable in our model. A systematic multivariate Cox regression was performed. Results Our Final Model stated that nulliparous women had 2.5 times more chances of having longer TTVD than primiparous (p < 0.001, CI 1.76–3.8), and 3.4 times more (p = 0.015, CI 1.27–9.25) than multiparous. Women with oxytocin-augmented labor had 2.05 times more chances (p = 0.001, CI 1.31–3.22) of having longer TTVD than patients without oxytocin. An induced partum had 3.8 times more chances (p < 0.001, CI 2.09–6.8) of having longer TTVD compared to a spontaneous partum. Conclusion Parity, labor augmentation, induction of labor and fetal weight determine TTVD; axial analgesia-related factors do not contribute to the model.