Other causes of PPH

The most common reason for a primary postpartum haemorrhage is the uterus not contracting efficiently enough or relaxing intermittently in the hours following the birth, allowing the bleeding to become heavy. The medical term for this is 'uterine atony', (atony meaning 'no tone' in the muscles of the uterus).

In an uncomplicated 3rd stage, the uterus should start to contract as soon as the placenta begins separating, contracting very tightly once the placenta is totally expelled from the uterus. It continues to contract in the hours following the birth. If the uterus does not contract adequately (within the first 24 hours), the bleeding becomes much heavier than expected. After this period of time, heavy bleeding will tend to be caused by either an infection or part of the placenta being retained.

The muscles in the uterus need to contract and retract to naturally stem the flow of blood. The uterine muscles criss-cross and intertwine, usually in the shape of a figure 8, encasing the blood vessels within the openings of the loops of the '8 shapes'. As the placenta separates, the muscles twist and contract, 'the loops of the 8' acting like tourniquets on the torn blood vessels, stemming the flow of blood to control the bleeding.

Many 'atonic' postpartum haemorrhages are unpredictable and unexpected. In attempts to predict who will experience a PPH, caregivers have compiled a list of 'categories' of women who could be at a slightly increased risk. It should be borne in mind that most women in these groups will have normal blood losses after giving birth.

The categories of increased risk for uterine atony are:

A long labour
A fast labour
A full bladder
Stress after the birth
A past history of a primary PPH
The uterus was 'over-distended' in the pregnancy