Lying in after giving birth has a long tradition but carries a risk of thrombosis. Blood clots form in leg veins and may embolise to the lungs, causing death. Early CEMD Reports did not recognise the benefits of early ambulation but divided thromboembolism deaths into three groups – during pregnancy, after vaginal delivery and after caesarean section. The Reports identified risk factors including age, obesity and caesarean section, and found that warning symptoms were being ignored. Shorter hospital stay reduced the number of deaths after vaginal birth. Caesarean section rates rose and an Enquiry into Perioperative Deaths (modelled on the CEMD) revealed the risk factors for post-operative thromboembolism. An 1995 an RCOG report advised on preventive measures including anticoagulants, previously avoided lest they cause bleeding. A sharp fall in deaths after caesarean section followed in 1997-9. By then thromboembolism was the leading Direct cause of maternal death and the benefits of guidelines had become clear. In 2004 the RCOG published a guideline on thromboprophylaxis in pregnancy and in 2006-8 thomboembolism fell to third place among causes of Direct death.