For a study, researchers wanted to determine the relative influence of changes in patient demographics and physician management to changes in the cesarean delivery rate in labor among nulliparous women. From 1992 to 2018, they conducted a retrospective cohort analysis of 485,451 births to nulliparous women who had labored at or after 35 weeks of gestation in Alberta, Canada. The information came from a provincial perinatal database. Cesarean delivery was the primary result. Multivariate logistic regression and population attributable risk calculation for identified risk variables were carried out.

The cesarean delivery rate grew from 12.5% in 1992 to 24% in 2018. Over the research period, the prevalence of maternal risk factors for cesarean delivery, including obesity, maternal age 35 years or older at birth, and comorbidities, rose. This, however, does not explain the rise in cesarean birth, because the frequency of cesarean delivery rose regardless of risk status. Furthermore, the population-attributable risk for each risk factor remained consistent throughout the research period. For example, the number of cesarean births attributed to this factor (the population-attributable risk) was 0.9 per 100 deliveries in 1992–1998 and 1 per 100 in 2014–2018 for mothers aged 35 or older at delivery. The proportion of cesarean births performed due to unsatisfactory fetal conditions grew from 30.1% in 1992 to 51.1% in 2018. Cesarean delivery in the second stage of labor climbed from 3.1% in 1992 to 5.9% in 2018. This was attributed to a considerable rise in cesarean delivery without a forceps trial among those who entered the second stage, from 2.5%in 1992 to 7.0% in 2018.

The observed tripling of cesarean delivery in labor among first-time moms was not caused by patient risk factors. Significant variables were an increase in the rate of cesarean delivery for unsatisfactory fetal conditions and a reduction in operational vaginal births.