Incidence and causes of maternal mortality in the USA

To characterize the most common causes and risk factors of maternal mortality in the USA and observe trends over the past 9 years.

We carried out a population-based retrospective cohort study using data from the Health Care Cost and Utilization Project, Nationwide Inpatient Sample. Women who were pregnant between 2003 and 2011 were identified. Baseline characteristics of pregnant women who died and those who lived were measured. ICD-9 codes for each cause of death were examined by up to three independent reviewers. Causes of death were categorized into the nine most common subgroups and trends were examined by tertiles of the period 2003-2011.

During this 9-year period, there were approximately 7 million births and 1102 maternal deaths, for an overall incidence of 14.2 per 100 000 births. Primary causes of maternal death included sepsis (20.6%), cardiac disease (17.8%), hemorrhage (16.2%), venous thromboembolism (15.2%), and hypertensive disorders (9.4%). During the study period, there was a significant decrease in the frequency of sepsis from 33.2% to 10.0% and a non-significant decrease in venous thromboembolism from 19.1% to 12.9%. There were increases noted in all other groups, notably in terms of hemorrhage from 8.2% to 22.0% and hypertensive disorders from 2.1% to 16.4%.

Maternal mortality remains a rare event. Although sepsis was the overall predominant cause of mortality during the study period, frequency declined over time and it was surpassed by hemorrhage and hypertensive disorders as the leading causes of maternal mortality.