1. WHO Maternal death surveillance and response: technical guidance information for action to prevent maternal death 2013 http://www.who.int/maternal_child_adolescent/documents/maternal_death_surveillance/en/
2. WHO Beyond the numbers: reviewing maternal deaths and complications to make pregnancy safer 2004 http://www.who.int/maternal_child_adolescent/documents/9241591838/en/
3. Institute of Medicine (US). Committee on Quality of Health Care in America Crossing the quality chasm: a new health system for the 21st century National Academy Press 2001 https://www.nationalacademies.org/hmd/~/media/Files/Report%20Files/2001/Crossing-the-Quality-Chasm/Quality%20Chasm%202001%20%20report%20brief.pdf