There are well documented differences between the characteristics of labour in primigravidae and multigravidae. The present study was undertaken to determine whether the gestational age and mode of delivery of a woman's first baby influences the characteristics of labour in her next pregnancy. Information regarding previous obstetric history and subsequent obstetric performance was derived from a database of 75,974 consecutive singleton births. As a group, women with a history of one preterm vaginal delivery had labour characteristics similar to those women whose one previous pregnancy had resulted in a vaginal delivery at term. When this group were analysed by the gestation at which the previous birth had occurred, a gestation-dependent effect was seen. Women whose first birth had been at less than 28 weeks gestation behaved in a similar manner to primiparous women. On the other hand, the characteristics of labour in women whose first birth had occurred between 33 and 36 weeks gestation were similar to those of women who had had a previous vaginal delivery at term. Women whose first delivery had been by caesarean section behaved in a similar manner to primiparae. The typical differences between the characteristics of first and second labours are the result of a gradual change which appears to be related to the gestation at which the first birth occurred.