In a multipara, the most common cause of Postpartum Haemorrhage is?

Uterine atony is a loss of tone in the uterine musculature. Normally, contraction of the uterine muscles during labor compresses the blood vessels and reduces flow, thereby increasing the likelihood of coagulation and preventing hemorrhage. A lack of uterine muscle contraction, however, can lead to an acute haemorrhage, as the uterine blood vessels are not sufficiently compressed. Clinically, 75-80% of postpartum haemorrhages are due to uterine atony.