Ranked Severe Maternal Morbidity Index for Population-Level Surveillance by Mode of Delivery

To determine which severe maternal morbidity indicators identify the most in-hospital mortality during delivery hospitalization by delivery mode.

We obtained data from the 1993-2015 Healthcare Cost and Utilization Project's National Inpatient Sample. Separate analyses were conducted for cesarean and vaginal deliveries. We ranked 22 severe maternal morbidity indicators by their overall population-attributable fraction of in-hospital mortality.

We identified 87,864,173 delivery hospitalizations; 27.9% were cesarean deliveries and 72.1% were vaginal deliveries. There were 6,686 records with a discharge disposition of "died," with the most occurring for cesarean deliveries (71.2%). Most deaths had a severe maternal morbidity indicator (cesarean deliveries = 94.2%; vaginal deliveries = 73.5%). Among cesarean deliveries, the top five ranked indicators were as follows: cardiac arrest/ventricular fibrillation, conversion of cardiac rhythm, ventilation, temporary tracheostomy, and aneurysm. Among vaginal deliveries, the top five ranked indicators were as follows: conversion of cardiac rhythm, cardiac arrest/ventricular fibrillation, ventilation, temporary tracheostomy, and amniotic fluid embolism. The top three ranked indicators identified 78.8% of in-hospital mortality among cesarean deliveries and 66.0% of in-hospital mortality among vaginal deliveries.

Severe maternal morbidity indicator rankings for cesarean and vaginal deliveries were similar; however, there were differences by delivery mode in the performance of the SMM indicators in identifying in-hospital deaths. Our findings underscore the need for the improved documentation and measurement of severe obstetric complications during pregnancy and the postpartum period at the population level.