Characteristics of normal labor.

The length of the first and second stages of labor was evaluated in 6991 women with singleton gestations at 37-42 weeks with vertex presentation. All patients delivered spontaneously without the use of oxytocin. Four study groups were created based on parity and whether conduction anesthesia was used. The mean lengths and limits (95th percentile) for the first stage of labor, respectively, were as follows: nulliparas: no anesthesia--8.1 and 16.6 hours, conduction anesthesia--10.2 and 19.0 hours; multiparas: no anesthesia--5.7 and 12.5 hours, conduction anesthesia--7.4 and 14.9 hours. Similar data for the second stage were as follows: nulliparas: no anesthesia--54 and 132 minutes, conduction anesthesia--79 and 185 minutes; multiparas: no anesthesia--19 and 61 minutes, conduction anesthesia--45 and 131 minutes. These statistical parameters are useful for defining when a labor becomes abnormal and intervention should be considered.