Uterine atony emerges as leading cause of postpartum haemorrhage

Postpartum haemorrhage most commonly occurs due to uterine atony, according to a systematic review and meta-analysis. Other causes include genital tract trauma, retained placenta, abnormal placentation, and coagulopathy.

Researchers searched multiple online databases for cohort studies of postpartum haemorrhage to identify and quantify the various causes and risk factors. Risk factors were classified as having weak, moderate, or strong association based on the pooled odds ratios (ORs): >1 to 1.5 (weak), >1.5 to 2 (moderate), and >2 (strong).

A total of 327 studies, which involved 847,413,451 women, were included in the meta-analysis. There was no restriction on age, race, or ethnicity. Methodological quality was high for most studies.

Using a random-effects model, pooled data showed that the five commonly reported causes of postpartum haemorrhage were uterine atony (70.6 percent; n=834,707, 14 studies), genital tract trauma (16.9 percent; n=18,449, six studies), retained placenta (16.4 percent; n=235,021, nine studies), abnormal placentation (3.9 percent; n=29,638, two studies), and coagulopathy (2.7 percent; n=236,261, nine studies). Of note, 7.8 percent of women had multiple postpartum haemorrhage causes (n=666, two studies).

Postpartum haemorrhage was strongly associated with anaemia, previous postpartum haemorrhage, caesarean birth, female genital mutilation, sepsis, no antenatal care, multiple pregnancy, placenta praevia, assisted reproductive technology use, macrosomia with a birthweight of more than 4,500 g, and shoulder dystocia.

Risk factors showing a moderate association with postpartum haemorrhage included BMI ≥30 kg/m², COVID-19 infection, gestational diabetes, polyhydramnios, pre-eclampsia, and antepartum haemorrhage. Finally, a weak association with postpartum haemorrhage was observed for Black and Asian ethnicity, BMI 25–29.9 kg/m², asthma, thrombocytopenia, uterine fibroids, antidepressant use, induction of labour, instrumental birth, and premature rupture of membranes.

The finding of uterine atony being the leading cause of postpartum haemorrhage supports the WHO recommendation for all women giving birth to be given prophylactic uterotonics.