According to a study published in the "Lancet" which covered the period from 1990 to 2013, the most common causes are postpartum bleeding (15%), complications from unsafe abortion (15%), hypertensive disorders of pregnancy (10%), postpartum infections (8%), and obstructed labor (6%). Other causes include blood clots (3%) and pre-existing conditions (28%). Maternal mortality caused by severe bleeding and infections are mostly after childbirth. Indirect causes are malaria, anemia, HIV/AIDS, and cardiovascular disease, all of which may complicate pregnancy or be aggravated by it. Risk factors associated with increased maternal death include the age of the mother, obesity before becoming pregnant, other pre-existing chronic medical conditions, and cesarean delivery.