To determine whether changes in risk factors for postpartum hemorrhage (PPH) over time are associated with a rise in postpartum hemorrhage rates.

Methods
Population-based study using linked hospital discharge and birth records from New South Wales, Australia for 752,374 women giving birth, 1994–2002. Analyses include a description of trends and regression analysis of risk factors for postpartum hemorrhage and comparison of predicted and observed rates of postpartum hemorrhage over time.

Results
Increasing proportions of women aged 35 years or older, born overseas, nulliparous, having cesarean births, having inductions and/or epidurals, postterm deliveries and large babies were evident. Observed postpartum hemorrhage rates increased from 4.7 to 6.0 per 100 births (P

< 0.001) while expected rates, adjusted for covariates, remained steady (P = 0.28).

Conclusion
Increases in postpartum hemorrhage are not explained by the changing risk profile of women. It may be that changes in management and/or reporting of postpartum hemorrhage have resulted in higher postpartum hemorrhage rates.

Keywords: Postpartum hemorrhage; Epidemiology; Childbirth; Morbidity; Data linkage

_{J.B. Ford, C.L. Roberts, J.M. Simpson, J. Vaughan and C.A. Cameron
Department of Obstetrics and Gynaecology, Northern Clinical School, University of Sydney, New South Wales, Australia
School of Public Health, University of Sydney, New South Wales, Australia
Royal Prince Alfred Hospital, Camperdown, Sydney, Australia}