Placental weight and excess postpartum haemorrhage: a population study of 308,717 pregnancies

To investigate whether placental weight may be positively associated with the prevalence of excess postpartum haemorrhage because large placentas have large surface areas.

Registry-based cross-sectional study.

Population study.

All singleton deliveries after 21 weeks of gestation in Norway during 1999-2004 (n = 308,717).

Data were obtained from the Medical Birth Registry of Norway, which is based on compulsory notification of births by the midwife or doctor in charge of the delivery.

Excess postpartum haemorrhage was defined as bleeding of 500 ml or more within 2 hours of delivery.

There was a gradual increase in the prevalence of excess postpartum haemorrhage with increasing placental weight (test for trend, P < 0.05). Having a placenta of 1100 g or more was associated with 2.5 times (odds ratio 2.54, 95% CI 2.31-2.79) higher prevalence than having a placenta of 300-499 g, after adjustment for offspring birthweight, parity, caesarean section and placenta-related and delivery-related complications. A large placenta relative to birthweight was also associated with higher prevalence of excess postpartum haemorrhage.

The size of the placental surface may explain the positive association of placental weight with the prevalence of postpartum haemorrhage. In pregnancies with a large placenta relative to offspring birthweight, other factors that enhance bleeding may also play a role.