Women in the United States are more likely to die from childbirth- or pregnancy-related causes than other women in the developed world, and half of those deaths may be preventable, according to the Centers for Disease Control and Prevention. The CDC's pregnancy mortality surveillance system was implemented in 1986 to track maternal deaths. Since then, the number of reported pregnancy-related deaths nationwide steadily increased from 7.2 deaths per 100,000 live births in 1987 to 17.8 per 100,000 in 2009 and 2011. It remains complicated to answer why there has been a rise in deaths and why black women are more affected than women of other races, said Dr. Michael Lindsay, associate professor at the Emory University School of Medicine and chief of service for gynecology and obstetrics at Grady Memorial Hospital in Atlanta. Though maternal deaths are rare in the United States, many doctors and researchers have varying ideas about what factors could be driving this longstanding racial disparity in death rates. Some point to the differences in overall health and chronic illnesses among black and white women as a driving factor for the disparity.