Fig. 2. Kaplan-Meier curves for the length of labor. Arrows indicate median values of time. ( A ) Time to successful vaginal delivery. The difference in both of the median time to delivery was –34 min (95% CI, –58 to –12 min, P = 0.35). ( B ) The merged time to latent and active phase of the first stage of labor. The difference in both of the median time was –8 min (95% CI, –13 to –3 min, P = 0.84). ( C ) Time to latent phase of first stage of labor. The difference in both of the median time was –14 min (95% CI, –22 to –4 min, P = 0.67). ( D ) Time to active phase of first stage of labor. The difference in both of the median time was –19 min (95% CI, –37 to –8 min, P = 0.39). ( A to D ) Time 0 is the time of the analgesia request. ( E ) Time to the second stage of labor. The difference in the median time was –8 min (95% CI, –18 to –2 min, P = 0.92). ( F ) Time to delivery by Cesarean section. The difference in the median time was –35 min (95% CI, –55 to –20 min, P = 0.44). ( G ) Time to instrument-assisted delivery. The difference in the median time was –35 min (95% CI, –46 to –23 min, P = 0.53).