Duration of labour with spontaneous onset.

Among 2242 women with spontaneous onset of labour, the median duration of labour for those delivered vaginally was 8 1/4 hours in para 0, 5 1/2 hours in para 1 and 4 3/4 hours in para 2+ mothers. In the parity groups 0, 1 and 2+ 90% had delivered within 16 1/4 hours, 10 1/2 hours and 10 3/4 hours, respectively, while 10% of para 0 labours lasted less than 4 hours, 10% of para 1 labours less than 2 1/4 hours and finally 10% of para 2+ labours less than 2 hours. In the first stage of labour the latent phase (cervical dilatation less than 4 cm), was nearly 2.5 times as long as the active phase (cervical dilatation 4-10 cm). The second stage (cervical dilatation 10 cm-birth) had a median duration of 16 min in para 0 and approximately 10 min in para 1+ mothers. The length of the latent and active phases and the second stage for para 1+ mothers was 60-70% of that of para 0 mothers. In individual mothers there were weak correlations between the length of the phases and stages. For example, the length of the latent phase appeared to be a relatively poor predictor of the length of the active phase of labour. However, selection bias may have weakened these correlations somewhat.