One way to examine the impact of interventions is to explore the consequences of what has been termed the “cascade of intervention,” with one intervention increasing the likelihood of others that may be used to monitor, prevent, or treat its side effects. This relationship was studied by Tracy et al. (2007) with over 750,000 low-risk women in a population-based study in Australia and is modeled on a presentation made at the 2011 Normal Birth Conference by Allison Shorten, PhD.
In Listening to Mothers III, we examine the relationship between cesarean rate, induction, and epidural usage. The maternal risk factors for induction are not taken into account in this initial descriptive presentation, though we intend to explore this question further.
The above figure presents an example of term births to first-time mothers who were not planning a cesarean and thus experienced labor. Of these mothers, 47% experienced an induction. Of those having an induction, 78% had an epidural, and of those mothers who had both an attempted induction and an epidural, the unplanned cesarean rate was 31%. Those who experienced either labor induction or an epidural, but not both, had cesarean rates of 19% to 20%. For those first-time mothers who neither experienced attempted induction nor epidural, the unplanned cesarean rate was 5%.
More analysis will be necessary to determine if the relationship is impacted by medical risk factors that may account for all three interventions, but the stark differences in cesarean rates between those mothers who start down the path of interventions with an induction and those mothers who do not are a powerful place to begin the analysis.