The 4Ts with the causes of bleeding that occur after childbirth. Specifically, this term refers to: tone, trauma, tissue and thrombin.
Tone or uterine atony is the most common cause of obstetric haemorrhage and is usually caused by overdistension of the uterus. Thus, multiple pregnancy is a risk factor for uterine atony.
Trauma accounts for 20% of cases of postpartum haemorrhage and is due to tearing of the birth canal, inversion of the uterus or uterine rupture.
Nine per cent of postpartum haemorrhages are due to retained placental tissue or placental abnormalities.
Finally, the remaining 1% are due to coagulation or thrombin abnormalities.