Retained placenta is a condition in which all or part of the placenta or membranes remain in the uterus during the third stage of labour. Retained placenta can be broadly divided into:
failed separation of the placenta from the uterine lining
placenta separated from the uterine lining but retained within the uterusA retained placenta is commonly a cause of postpartum haemorrhage, both primary and secondary.Retained placenta is generally defined as a placenta that has not undergone placental expulsion within 30 minutes of the baby’s birth where the third stage of labor has been managed actively. [Source: Wikipedia 
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