Risk factors and between-hospital variation of caesarean section in Denmark: a cohort study

OBJECTIVES The aim of this study was to estimate the effects of risk factors on elective and emergency caesarean section (CS) and to estimate the between-hospital variation of risk-adjusted CS proportions. DESIGN Historical registry-based cohort study. SETTINGS AND PARTICIPANTS The study was based on all singleton deliveries in hospital units in Denmark from January 2009 to December 2012. A total of 226 612 births by 198 590 mothers in 29 maternity units were included. PRIMARY AND SECONDARY OUTCOME MEASURES We estimated (1) OR of elective and emergency CS adjusted for several risk factors, for example, body mass index, parity, age and size of maternity unit and (2) risk-adjusted proportions of elective and emergency CS to evaluate between-hospital variation. RESULTS The CS proportion was stable at 20%-21%, but showed wide variation between units, even in adjusted models. Large units performed significantly more elective CSs than smaller units, and the risk of emergency CS was significantly reduced compared with smaller units. Many of the included risk factors were found to influence the risk of CS. The most important risk factors were breech presentation and previous CS. Four units performed more CSs and one unit fewer CSs than expected. CONCLUSION The main risk factors for elective CS were breech presentation and previous CS; for emergency CS they were breech presentation and cephalopelvic disproportion. The proportions of CS were stable during the study period. We found variation in risk-adjusted CS between hospitals in Denmark. Although exhaustive models were applied, the results indicated the presence of systematic variation between hospital units, which was unexpected in a small, well-regulated country such as Denmark.