Objective: Caesarean delivery rates continue to rise globally the reasons for which are poorly understood. We aimed to characterize attributable factors for increasing caesarean delivery rates over a 30-year period within our health network. Design: Observational cohort study. Setting: Two hospitals (large tertiary referral hospital and metropolitan hospital) in Sydney, Australia, across two time periods: 1989-1999 and 2009-2016, between which the caesarean delivery rate increased from 19% to 30%. Participants: All women who had a caesarean delivery after 24 weeks gestation Methods: Data were analysed using multiple imputation and robust Poisson regression to estimate the changes in the caesarean delivery rate attributable to maternal and clinical factors. Main outcome measures: Caesarean delivery. Results: Fifty-six percent of the increase in the rate of caesarean delivery was attributed to changes in the distribution of maternal factors including maternal age, body mass index, parity and history of previous caesarean delivery. When changes in the obstetric management of multiple gestation, malpresentation and preterm singleton birth were considered, 66% of the increase in caesarean rate was explained. When pre-labour caesarean deliveries for maternal choice, suspected fetal compromise, previous pregnancy issues and suspected large fetus were excluded, 78% of the increase was explained. Conclusions: Most of the steep rise in the caesarean delivery rate from 19% to 30% is attributable to changes in maternal demographic and clinical factors.