Mode of delivery is an independent risk factor for maternal mortality: a case-control study

In contrast to the global trend, the maternal mortality ratio (MMR) in the United States has increased in recent decades. During this time, the cesarean section rate has concurrently and steadily increased. Herein, we sought to determine whether the mode of delivery is an independent risk factor for maternal in-hospital mortality.

We conducted a retrospective, population-based, 1:1 matched, case-control study on all births recorded in the Health - Care Cost and Utilization Project - Nationwide Inpatient Sample between 2005 and 2014. We compared cases of maternal mortality and survival on a number of clinical characteristics. We conducted two different multivariate logistic regression analysis models, obtaining the adjusted odds ratios to determine the independent effect of mode of delivery on maternal mortality relative to surviving controls.

We found a total of 617 cases of maternal mortality, which corresponds to an in-hospital MMR of 6.9/100,000 in our cohort. We matched 617 controls to mortality cases by year and geographic location. Relative to surviving controls, cases of maternal mortality were older, more likely to be African American, of lesser income, more likely to use Medicaid as payment, to have prolonged admissions, and more likely to have severe obstetrical complications including preterm delivery, postpartum hemorrhage, eclampsia, peripartum cardiomyopathy, pulmonary emboli, and disseminated intravascular coagulation (DIC). Relative to unassisted vaginal delivery, adjusted logistic regression analysis reveals no excess mortality observed with assisted vaginal delivery: OR 1.35, 95% CI [0.59-3.51]. However, after adjusting for demographic and obstetrical confounders, a significant risk of maternal mortality was observed with cesarean delivery: OR 3.21, 95% CI [2.80-3.61], p-value = .0001. This risk was more pronounced amongst primary cesarean deliveries: OR 5.72, 95% CI [4.92-6.51], p-value = .0001.

Cesarean delivery, and particularly primary cesarean delivery, is an independent risk factor for maternal in-hospital mortality. Measures taken to reduce the cesarean section rate may impact the rising maternal mortality ratio (MMR) in the United States.