Postpartum haemorrhage (uterine atony)

Definition

Definition and causes

• Postpartum haemorrhage means blood loss from 500 ml vaginal / 1000 ml post-caesarean.
• The four Ts are tone, trauma, tissue, thrombin.
• The commonest cause is uterine atony (most common cause).
• Blood loss is underestimated, thus weighed.

• Traditionally, postpartum haemorrhage is defined as estimated blood loss of more than 500 ml after vaginal birth or more than 1000 ml at caesarean section.
• Since 2017, ACOG defines it as cumulative blood loss of more than 1000 ml with signs of hypovolaemia within 24 hours, regardless of the mode of birth.

Classification

• Primary haemorrhage occurs between the third stage and 24 hours after birth, secondary haemorrhage later than 24 hours and up to 12 weeks postpartum.

Occurrence & epidemiology

Epidemiology

• Postpartum haemorrhage is the leading cause of maternal death in low-income countries and of severe maternal morbidity in many high-income countries.

Aetiopathogenesis

What is different here

• In pregnancy, clotting is physiologically activated.
• Blood loss is further masked by the increased blood volume of pregnancy.

Aetiology and risk factors

• Causes are summarised as the 4 Ts: tone (atony), trauma (lacerations, uterine rupture), tissue (retained placental tissue) and thrombin (coagulation disorders).
• The commonest cause is uterine atony, which usually occurs within the first hour after birth; risk factors include uterine overdistension (multiple pregnancy, polyhydramnios, fetal anomaly, large fetus), prolonged or dysfunctional as well as rapid labour, grand multiparity, relaxant anaesthetics and chorioamnionitis.
• Further causes are genital tract lacerations, extension of an episiotomy, uterine rupture, bleeding disorders, retained placental tissue, haematoma, uterine inversion, infection and subinvolution of the placental site, which usually occurs early but may occur as late as one month after birth; fibroids and a previous postpartum haemorrhage also increase the risk.

Clinical features

More facts from the study questions

• Methylergometrine can increase blood pressure.
• It is therefore contraindicated in hypertensive disorders such as pre-eclampsia.
• The four “Ts” (Tone, Trauma, Tissue, Thrombin) summarise the causes.
• Atony (loss of tone) is by far the most frequent cause.
• The Bakri balloon is an established method for intrauterine tamponade.
• Chitosan gauze (e.g. Celox) is another option, albeit off-label.
• Visual estimation of blood loss is notoriously unreliable and usually leads to underestimation.
• During pregnancy, fibrinogen levels are physiologically much higher than in the non-pregnant state.
• A drop to a 'normal' level already indicates a relevant consumption.
• The lethal triad of coagulopathy is hypothermia, acidosis and hypocalcaemia.

Diagnosis

Laboratory work-up

• Viscoelastic tests (ROTEM/TEG) give rapid point-of-care results on coagulation.
• The lethal triad of coagulopathy is hypothermia, acidosis, hypocalcaemia.

• Blood loss is routinely underestimated clinically, in studies by 46 to 75%, and the more so the larger the loss; quantitative measurement methods are more accurate but have not consistently improved outcomes.

Keep learning in the app

Further reading (selection)

1. StatPearls: Postpartum Hemorrhage (NCBI Bookshelf)
2. MSD Manual Professional Edition: Postpartum Hemorrhage
3. BMC Pregnancy Childbirth 2015: Is accurate and reliable blood loss estimation the crucial step in early detection of postpartum haemorrhage? (PMC, open access)
4. DocCheck Flexikon, Postpartale Blutung

Cross-references