Curtin SC,.Park MM. Trend in the attendant, place, and timing of births, and in the use of obstetric interventions: United States, 1989-97. National Vital Statistics Reports from the Centers for Disease Control and Prevention 1999;47:1-16.
countries with civil registration data characterized as complete with good attribution of cause of death
Trends in Maternal Mortality: 1990-2008. WHO/UNICEF/UNFPA/WB