OBJECTIVE: To identify the factors underlying the recent increase in maternal mortality ratios (maternal deaths per 100,000 live births) in the United States.
METHODS: We carried out a retrospective study with data on maternal deaths and live births in the United States from 1993 to 2014 obtained from the birth and death files of the Centers for Disease Control and Prevention. Underlying causes of death were examined between 1999 and 2014 using International Classification of Diseases, 10th Revision (ICD-10) codes. Poisson regression was used to estimate maternal mortality rate ratios (RRs) and 95% confidence intervals (CIs) after adjusting for the introduction of a separate pregnancy question and the standard pregnancy checkbox on death certificates and adoption of ICD-10.
RESULTS: Maternal mortality ratios increased from 7.55 in 1993, to 9.88 in 1999, and to 21.5 per 100,000 live births in 2014 (RR 2014 compared with 1993 2.84, 95% CI 2.49–3.24; RR 2014 compared with 1999 2.17, 95% CI 1.93–2.45). The increase in maternal deaths from 1999 to 2014 was mainly the result of increases in maternal deaths associated with two new ICD-10 codes (O26.8, ie, primarily renal disease; and O99, ie, other maternal diseases classifiable elsewhere); exclusion of such deaths abolished the increase in mortality (RR 1.09, 95% CI 0.94–1.27). Regression adjustment for improvements in surveillance also abolished the temporal increase in maternal mortality ratios (adjusted maternal mortality ratios 7.55 in 1993, 8.00 per 100,000 live births in 2013; adjusted RR 2013 compared with 1993 1.06, 95% CI 0.90–1.25).
CONCLUSION: Recent increases in maternal mortality ratios in the United States are likely an artifact of improvements in surveillance and highlight past underestimation of maternal death. Complete ascertainment of maternal death in populations remains a challenge even in countries with good systems for civil registration and vital statistics.
Recent increases in maternal mortality ratios in the United States are likely an artifact of improvements in surveillance.
Department of Obstetrics and Gynaecology and the School of Population and Public Health, University of British Columbia, and the Children's and Women's Hospital and Health Centre of British Columbia, Vancouver, British Columbia, Canada; the Department of Obstetrics and Gynaecology, College of Medicine, King Saud University, Riyadh, Saudi Arabia; the Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada; and the Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.
Corresponding author: K. S. Joseph, MD, PhD, Department of Obstetrics and Gynaecology, Women's Hospital of British Columbia, Room C403, 4500 Oak Street, Vancouver, BC V6H 3N1, Canada; email: email@example.com.
Ms. Muraca is the recipient of a Vanier Canada Graduate Scholarship and is also supported by a Canadian Institutes of Health Research (CIHR) grant on severe maternal morbidity (MAH-15445). Dr. Joseph is supported by the British Columbia Children's Hospital Research Institute and holds a CIHR Chair in maternal, fetal, and infant health services research (APR-126338).
Each author has indicated that he or she has met the journal's requirements for authorship.
Financial Disclosure The authors did not report any potential conflicts of interest.