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- Page navigation anchor for Key considerations when comparing outcomes by mode of delivery raise questions about study validity and clinical relevanceKey considerations when comparing outcomes by mode of delivery raise questions about study validity and clinical relevance
Korb and colleagues(1) investigated the important and complex issue of cesarean delivery and subsequent severe acute maternal morbidity (SAMM). Observational studies comparing maternal and perinatal outcomes following vaginal and cesarean delivery have been criticized for inappropriate comparison groups and the inability to address confounding by indication. Despite efforts to overcome these challenges, the study by Korb and colleagues(1) is compromised by these same issues and consequently the results need to be interpreted with caution.
Firstly, comparing outcomes following successful vaginal and cesarean deliveries is misleading with respect to causal inference. Risks of an outcome across two interventions can be meaningfully contrasted only if those who received one intervention were candidates for receiving the other intervention. This is known as the principle of exchangeability,(2) which dictates that both groups should be exchangeable with respect to an outcome had they been subjected to the identical exposure.(3) However, a successful vaginal delivery is an impossibility for a substantial fraction of women who deliver by cesarean. To address this limitation, in 2006 the NIH State-of-the-Science expert panel on cesarean delivery recommended that all future research comparing maternal and neonatal outcomes following vaginal and cesarean delivery be based on planned vaginal versus planned cesarean delivery.(4) Korb and colleagues(1) applied this approach in a...
Show MoreCompeting Interests: None declared. - Page navigation anchor for Delivery options and risk of severe maternal morbidityDelivery options and risk of severe maternal morbidity
Korb and colleagues1 caution women and obstetricians about the increased risks of severe acute maternal morbidity (SAMM) associated with cesarean delivery based on their non-experimental study. We have a few comments on concepts, methods and interpretation.
The conceptual concern relates to the study’s primary analysis. Whereas Korb and colleagues1 evaluated cesarean delivery and vaginal delivery as alternative modes of delivery, these are not management options available or offered in modern obstetrics. Available instead are two management algorithms, namely, planned cesarean delivery and planned vaginal delivery.2-4 Therefore, the only clinically relevant finding in the study by Korb and colleagues1 is that of no significant increase in SAMM risk following planned cesarean delivery (adjusted odds ratio 1.09, 95% confidence interval 0.85-1.41).
The use of propensity score methods to control confounding by indication reveals a disconnection between clinical and statistical issues: indication (for cesarean delivery) is a complex construct not amenable to accurate quantification, while propensity score analysis requires precise quantification of indication for complete control of confounding.5 The paper by Korb and colleagues1 provided no information on the indications for cesarean delivery, and the analysis controlled for some less relevant and some more relevant factors (e.g., country of birth and prior cesarean delivery), in lieu of controlling for confou...
Show MoreCompeting Interests: None declared.