Risk of severe maternal morbidity associated with cesarean delivery and the role of maternal age: a population-based propensity score analysis

BACKGROUND: Short-term maternal complications of cesarean delivery remain uncertain because of confounding by indication. Our objective was to assess whether cesarean delivery is associated with severe acute intra- or postpartum maternal morbidity compared with vaginal delivery, overall and according to the timing of the cesarean.

METHODS: We performed a case–control analysis using data from EPIMOMS, a prospective population-based study of deliveries at 22 gestation weeks or later from 6 regions of France in 2012–2013. Cases of intra- or postpartum severe acute maternal morbidity that were not a result of a condition present before delivery were compared with controls randomly selected in a 1/50 ratio. Associations between delivery modes and severe acute maternal morbidity were estimated in a propensity score–matched sample.

RESULTS: Among 182 300 deliveries, we identified 1444 cases and 3464 controls. The proportion of cesarean delivery was significantly higher among cases than controls (36.0% v. 18.2%). In the propensity score–matched analysis, cesarean deliveries were significantly associated with a higher risk of severe acute maternal morbidity (adjusted odds ratio [OR] 1.8, 95% confidence interval [CI] 1.5–2.2). This association increased with maternal age and was particularly marked for women aged 35 years or older (adjusted OR 2.9, 95% CI 1.9–4.4). This increased risk was significant for cesarean deliveries during labour in women of all age groups and for those before labour only in women aged 35 years or older (adjusted OR 5.1, 95% CI 2.3–11.0).

INTERPRETATION: Cesarean delivery is associated with a higher risk of severe acute maternal morbidity than vaginal delivery, particularly in women aged 35 years and older. Clinical decisions regarding delivery mode should account for this excess risk accordingly.

Cesarean delivery is a useful intervention for mothers and newborns in many situations. Nonetheless, its rates have soared over the past 20 years in most developed countries, where more than 1 out of 5 women deliver by cesarean.1 The range of indications for cesarean delivery appears to have broadened considerably, with more cesarean deliveries likely to be performed for questionable medical indications.2–7 This increase requires evaluation of its potential adverse consequences on maternal and neonatal health.

The long-term obstetric risks associated with the presence of a scarred uterus in future pregnancies are well recognized, primarily uterine rupture and abnormal placentation.8–13 Conversely, conclusions about the comparative short-term maternal risks of cesarean and vaginal delivery remain unclear. A randomized controlled trial among women with no medical indication for cesarean delivery is, at best, ethically questionable. Observational studies can provide relevant information to address this, but their conclusions are likely to be limited owing to confounding by indication. That is, the fact that maternal morbidity may be a result of the condition indicating or justifying the cesarean delivery rather than to the surgical procedure itself can produce an apparent association between cesarean delivery and maternal morbidity.

Earlier studies of the association between maternal mortality and mode of delivery have shown a higher risk of maternal mortality associated with cesarean versus vaginal deliveries.14,15 These studies, however, were limited by their retrospective design, the rarity of maternal deaths and insufficient consideration of this confounding by indication. Over the past 10 years, numerous observational studies have reported discordant results about the association between cesarean and severe maternal morbidity, and their conclusions too are limited by several methodological flaws: insufficient control for confounding by indication, inappropriate definition of severe acute maternal morbidity, retrospective designs limiting quality and availability of data, non–population-based designs restricting the generalizability of results and failure to differentiate between cesarean delivery before or during labour.16–20

One of the aims of the EPIMOMS prospective population-based study, which was specifically designed to study severe acute maternal morbidity, was to explore its association with cesarean delivery. Our objective here is to test for — and if it exists, quantify — the association between intra- or postpartum severe acute maternal morbidity and cesarean versus vaginal delivery, overall and according to the timing of cesarean delivery, before or during labour. This analysis focused especially on controlling confounding by indication, first by careful selection of the women analyzed, excluding situations at high risk of confounding by indication, and then by using propensity scores to control for residual confounding by indication.

Full article: Canadian Medical Association Journal

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