Variation in caesarean delivery rates

Rising rates of delivery by caesarean section are a cause of concern worldwide. Wide variation has been noted between countries—for example, caesarean delivery rates are 15% in the Netherlands but 38% in Italy.1 More than twofold differences in primary caesarean delivery rates have also been reported across regions in Canada,2 and between hospital delivery units in the United States and Australia.3 4 Although there is no consensus concerning the optimal caesarean delivery rate, it is clear that poor access to emergency obstetric care, and hence poor access to caesarean delivery, can harm both mother and infant.5 Conversely, high rates of operative delivery may result in poorer maternal and infant outcomes for the current or subsequent births.6 7 Variations in caesarean delivery rates have been attributed to differences in the characteristics of women giving birth. In the linked study (doi:10.1136/bmj.c5065), Bragg and colleagues assess whether the variation in unadjusted caesarean section rates between NHS trusts in England can be explained by maternal characteristics and clinical risk factors[f1].8

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BSIP, Boucharlat/Science Photo Library

Previous studies have shown that women are more likely to be delivered by caesarean section if they are in their first pregnancy; older; have previously delivered by caesarean section; have a breech presentation; deliver preterm; or have other complications of pregnancy or medical problems, including diabetes, hypertensive disorders of pregnancy, or obesity.9 10 However, comparisons of rates of caesarean delivery often fail to take these factors into account, with rates not adjusted for population differences in these characteristics. Bragg and colleagues show significant variation in the rates of caesarean delivery among NHS trusts in England, after adjustment for several of these factors.8 Although they were unable to investigate some potential explanations—including maternal obesity, indication for caesarean section, gestational age at delivery, and models of care—persisting differences in these factors are unlikely to account for the greater than twofold difference in caesarean delivery rates that they calculated—adjusted rates varied between 15% and 32% among the units investigated.

Other suggested reasons for variation in caesarean delivery rates include contrasting medico-legal environments, private compared with public healthcare systems, differences in delivery volumes, and differences in the training of junior obstetricians. These factors are unlikely to explain variation between units within the relatively uniform climate of NHS hospitals in England. Although maternal choice has also been cited as a potential reason for increases in rates of caesarean delivery, there is little evidence to suggest that this accounts for much variation in caesarean rates between hospitals. Variation is most probably related to differences in thresholds for intervention at institutional and practitioner levels and variations in the preferred models of care.

This research indicates, at a minimum, the need for more informed surveillance of caesarean sections at a hospital, regional, and national level. Several approaches could achieve this. Perhaps the most straightforward approach is the use of the “standard primipara,” whereby units collect specific data on a defined group of low risk women only. The “standard primipara” is a 20-34 year old woman, who is giving birth for the first time, free of obstetric and specific medical complications, and has a singleton term pregnancy with a non-small for gestational age infant in a cephalic presentation. Comparison of intervention rates in this group of women effectively controls for differences in population or case mix between units, and it has been used to show the impact of guidelines on intrapartum care.11 An extension of this approach is to divide women into 10 population subgroups according to specific combinations of distinct characteristics: parity, multiple pregnancy, fetal presentation, type of labour onset, gestation, and previous caesarean delivery. This approach allows comparison of caesarean delivery rates within comparable population subgroups, but it also allows units to establish the contribution to the total caesarean delivery rate made by women in each cohort,12 and hence to target approaches to reduce the total rate. Both of these approaches require specific data collection. Enhancement of routine data to improve the monitoring of obstetric care remains an option, but it is unlikely that compliance with evidence based practice can ever be monitored this way.

It is now 10 years since the national sentinel caesarean section audit in the UK, which examined practice in detail,10 and yet wide variation still exists. Unwarranted variation in clinical practice has been cited as an indication of a poor quality service.

Bragg and colleagues’ study provides the impetus for ongoing work to investigate and tackle the reasons for regional and subregional variations in caesarean section practice. As with the original audit, women and their families, clinicians, planners, policy makers, and hospitals would benefit from a more detailed examination of variations in caesarean delivery practice and the generation of the high quality evidence needed to inform practice guidelines. High quality population based observational studies can provide robust evidence where randomised controlled trials are not possible or unethical, and such studies should be encouraged. There is no place for poor guidelines based on poor evidence.