Duration of the second stage of labor.

The second stage of labor, defined as the time from full dilatation of the external os to delivery of the child, was recorded during a three-month period in 635 labors with vaginal delivery. The median duration in labors of spontaneous onset was 31.3 minutes in para 0 mothers, 14.3 minutes in para 1 mothers and 11.7 minutes in para 2 + mothers. In induced labors the second stage had approximately the same length as in labors with spontaneous onset. The time distribution showed that the second stage in para 0 mothers had a plateau in the 17.5--37.5 minute range, whereas para 1 + mothers had a sharper peak at 7.5 minutes. Forty and 45 minutes respectively seemed to be limits beyond which only very few second stages of labor lasted. Operative delivery terminated 18 per cent of para 0 labors and 6 per cent of the para 1 + labors entering the second stage. The operative interventions seemed to appear in two clusters for each parity group. It appeared that fetal asphyxia requiring intervention was discovered before 40 minutes of the second stage in para 0 and before 30 minutes in para 1 + mothers. Later operative termination was more often performed to relieve fatigued mothers.