Most common cause of secondary PPH is :

Retained placenta Secondary PPH Bleeding usually occurs between 8th to 14th day of delivery. Causes of late PPH : Retained bits of cotyledon or membranes (M.C.) Infection and separation of slough over a deep cervico - vaginal laceration. Endometritis and subinvolution of the placental site Ref : Dutta book of obstetrics 8th Ed.