An analysis from the National Perinatal Epidemiology Unit has estimated that almost 50% of the population attributable risk of maternal mortality is associated with the presence of a medical comorbidity. Using data from the Confidential Enquiry into Maternal Deaths, 135 cases of direct maternal death were identified between 2009 and 2012 from five major causes. Data from the UK Obstetric Surveillance System was used to identify 1,661 women who survived one of these five complications i.e. eclampsia, pulmonary embolism, severe sepsis, amniotic fluid embolism and peripartum haemorrhage. These survivors formed an unmatched control group.