Materials and methods
We analysed all women delivering at EH, both at Box Hill Hospital (BHH) and Angliss Hospital (AH), between the 1st of July 2014 and the 30th of June 2019. Births included live births and still births of at least 400 grams birthweight or at least 20 weeks of gestation. Both BHH and AH are teaching hospitals with supervision and support from senior clinicians 24 hours and with theatre availability. According to the capability framework for Victorian maternities 12 BHH is a level 5 hospital with 2500 deliveries per year and AH is a level 4 hospital with 2200 deliveries per year.
Data for all mothers and babies was collected retrospectively using the Birthing Outcomes System (BOS), developed by Management Consultants and Technology Services, in which information is routinely collected for all women presenting to EH. BOS is a clinical information management system integrating pregnancy and perinatal data which is widely used in Victorian maternity services. Data in BOS was reviewed and extracted following EH protocols (available on request). Data extracted included all the variables needed to classify women into one of the ten Robson groups. When additional information was required for clarifications full medical records were reviewed.
To assess the quality and the coverage of our data, the obtained BOS data was cross-referenced with the national birth registry to make sure there were no missing cases. Additionally, as per the Robson implementation manual 9 we compared the number of CS and women in our data with the number of CS and women who delivered in the hospital and lastly, we assessed the size and the CS rate of group 9 looking for misclassified cases.
As per the recommended Robson approach, the overall CS rate (percentage of women delivered by CS), the size of each group, the CS rate per group, and the absolute and relative contribution of each group to the overall CS rate were calculated. We used linear regression to analyse the trend of CS rate over time at BHH an, AH individually and EH as whole. Additionally, we compared the trend between BHH and AH. A chi square test was used to determine the differences between hospitals in each of the Robson groups. Data were analysed in STATA 16.
This study was considered by the Office of Research and Ethics at EH (reference QA19/097) and was deemed to have met the criteria for an Audit or Quality Assurance activity, therefore as per the National Health and Medical Research Council there was no requirement for Human Research Ethics review.