Recent studies have identified clinical features that are major risk factors for puerperal infection. Patients of low socioeconomic status undergoing cesarean section who have had prolonged labor and rupture of membranes (ROM) incur a 40 to 85% risk of endometritis. Infection occurs generally in less than 10% of women undergoing vaginal delivery, even when complicated by prolonged ROM, and often in considerably fewer cases. Other features such as internal monitoring, obesity, anemia, and general anesthesia have not been consistent determinants in recent studies.