National Rates of Uterine Rupture are not Associated with Rates of Previous Caesarean Delivery: Results from the Nordic Obstetric Surveillance Study

Background: Previous caesarean delivery and intended mode of delivery after caesarean are well-known individual risk factors for uterine rupture. We examined if different national rates of uterine rupture are associated with differences in national rates of previous caesarean delivery and intended mode of delivery after a previous caesarean delivery. Methods: This study is an ecological study based on data from a retrospective cohort in the Nordic countries. Data on uterine rupture were collected prospectively in each country as part of the Nordic obstetric surveillance study and included 91% of all Nordic deliveries. Information on the comparison population was retrieved from the national medical birth registers. Incidence rate ratios by previous caesarean delivery and intended mode of delivery after caesarean were modelled using Poisson regression. Results: The incidence of uterine rupture was 7.8/10 000 in Finland and 4.6/10 000 in Denmark. Rates of caesarean (21.3%) and previous caesarean deliveries (11.5%) were highest in Denmark, while the rate of intended vaginal delivery after caesarean was highest in Finland (72%). National rates of uterine rupture were not associated with the population rates of previous caesarean but increased by 35% per 1% increase in the population rate of intended vaginal delivery and in the subpopulation of women with previous caesarean delivery by 4% per 1% increase in the rate of intended vaginal delivery. Conclusion: National rates of uterine rupture were not associated with national rates of previous caesarean, but increased with rates of intended vaginal delivery after caesarean.