Fig. 12. Time of epidural placement and rate of labor progress. ( A ) active rate constants (λ1), ( B ) latent rate constants (λ2), and ( C ) the coefficient (C) as a function of the time of neuraxial analgesia initiation. The slope is significantly different from 0 for λ1(** P < 0.01) and λ2(* P < 0.05), suggesting that patients with slower labors are given neuraxial analgesia earlier in labor .