1. Saving mothers' lives: reviewing maternal deaths to make motherhood safer: 2006–2008. The Eighth Report of the Confidential Enquiries into Maternal Deaths in the United Kingdom;Lewis GE;BJOG,2011
2. United Nations.Millennium development goal 5: improve maternal health.2000.http://www.un.org/millenniumgoals/maternal.shtml. Accessed October 07 2015.