Trends in mode of delivery during 1984-2003: can they be explained by pregnancy and delivery complications?

OBJECTIVES: To describe trends in mode of delivery, to identify significant factors which affected mode of delivery, and to describe how these factors and their impact have changed over time.

DESIGN: Total population birth cohort.

SETTING: Western Australia 1984-2003.

PARTICIPANTS: The analysis was restricted to all singleton infants delivered at 37-42 weeks of gestation with a cephalic presentation (n = 432,327).

METHODS: Logistic regression analyses were undertaken to estimate significant independent risk factors separately for elective and emergency caesarean sections compared with vaginal delivery (spontaneous and instrumental), adjusting for potential confounding variables.

MAIN OUTCOME MEASURES: Trends in mode of delivery, demographic factors, and pregnancy and delivery complications. Estimated likelihood of elective caesarean section compared with vaginal delivery and emergency caesarean section compared with vaginal delivery.

RESULTS: Between 1984-88 and 1999-2003, the likelihood of women having an elective caesarean section increased by a factor of 2.35 times (95% CI 2.28-2.42) and the likelihood of an emergency caesarean section increased 1.89 times (95% CI 1.83-1.96). These caesarean section rate increases remained even after adjustment for their strong associations with many sociodemographic factors, obstetric risk factors, and obstetric complications. Rates of caesarean section were higher in older mothers, especially those older than 40 years of age (elective caesarean section, OR 5.42 [95% CI 4.88-6.01]; emergency caesarean section, OR 2.67 [95% CI 2.39-2.97]), and in nulliparous women (elective caesarean section, OR 1.54 [95% CI 1.47-1.61]; emergency caesarean section, OR 3.61 [95% CI 3.47-3.76]).

CONCLUSIONS: Our data show significant changes in mode of delivery in Western Australia from 1984-2003, with an increasing trend in both elective and emergency caesarean section rates that do not appear to be explained by increased risk or indication.