Monitoring operative delivery trends provides the opportunity to consider whether changes are in a direction that will achieve the best outcomes for mothers and their infants. The aims of this study were to identify trends in and predictors of operative delivery (forceps, vacuum or caesarean) among women who have labour; and to determine trends in the operative methods used. The study was based on 616 303 live, singleton, term births delivered between 1990 and 1997 in New South Wales, Australia. There was no change in the annual percentage of women who experienced labour and 20% had an operative birth during labour. The vacuum to forceps ratio declined from 1 : 6 in 1990 to 1 : 1 in 1997. Among women with labour, caesareans increased from 6.4% to 7.8%. For primiparae, the factors predictive of operative delivery (epidural analgesia, age > 34 years, induced or augmented labour and private care) did not change over time. A predictive model for multiparae did not have adequate fit, indicating the importance of data on prior birth history. Studies of trends in operative deliveries are most useful and consistent with decision making when interventions before the onset of labour and during labour are analysed separately. Furthermore, the vacuum:forceps ratio provides a useful tool for comparative analyses.