Postpartum haemorrhage following second birth in women with caesarean first birth: a population-based study

Postpartum haemorrhage (PPH) is a leading cause of maternal morbidity and mortality. Evidence regarding PPH risk following vaginal birth after caesarean (VBAC) compared to elective repeat caesarean section (ERCS) is inconsistent, partly due to heterogeneous study populations. This study assesses postpartum haemorrhage (PPH) and transfusion rates in second pregnancies among women with a prior caesarean birth, providing a clearer assessment of outcomes by mode of birth.

This population-based study included 18,872 women in Queensland with a primary caesarean birth followed by a singleton, cephalic birth at 37 weeks or more between 2011 and 2021. Mode of birth was classified as VBAC, caesarean section with labour, or ERCS. PPH was defined as 500 mL or more after vaginal birth or 1000 mL or more after caesarean. Modified Poisson regression estimated adjusted relative risks (aRRs) for PPH and transfusion.

Among 18,872 second births, PPH rates were highest for VBAC (13.8%), followed by caesarean with labour (7.5%) and ERCS (5.3%). Compared with ERCS, VBAC was associated with nearly three-fold higher PPH risk (aRR 2.99, 95% CI 2.59-3.46) and caesarean with labour with a 1.5-fold higher risk (aRR 1.54, 95% CI 1.30-1.82). Transfusion rates showed a similar gradient across modes of birth.

Among women with a prior caesarean and no previous vaginal birth, VBAC is associated with higher risks of postpartum haemorrhage and maternal transfusion compared with elective repeat caesarean section. These findings describe associations between actual mode of birth and haemorrhage outcomes and may contribute to counselling when interpreted alongside evidence on planned mode of birth.