Discussion
anaemia, death, bleeding
ANAEMIA, BLEEDING, POSTPARTUM HAEMORRHAGE, POSTPARTUM BLEEDING, POSTPARTUM HAEMORRHAGE
A low prebirth haemoglobin concentration greatly increases the probability of postpartum haemorrhage. The association between prebirth haemoglobin and postpartum haemorrhage is similar regardless of how postpartum haemorrhage is defined. Women with severe anaemia also have a greatly increased risk of death or near miss.To our knowledge, this is the largest cohort study of the association between prebirth haemoglobin and postpartum haemorrhage. The large sample size allowed us to examine maternal anaemia as a continuous rather than a categorical variable. Loss to follow-up was negligible and there were few missing data for any variable. Prebirth haemoglobin concentration was measured using capillary haemoglobinometry (HemoCue), which has been shown to be accurate and with the smallest bias in comparison with the reference standard. Postpartum haemorrhage was assessed clinically and objectively on the basis of measured haemoglobin change. The study dataset allowed us to control for many potential confounding factors for anaemia and postpartum haemorrhage risk.Several cohort studies have shown that maternal anaemia increases the risk of postpartum haemorrhage and death. Daru and colleaguesAlthough studies comparing haemoglobin concentration measured using capillary HemoCue and a reference standard laboratory measurement have shown that accuracy is high, some measurement error is inevitable.There are several mechanisms through which anaemia could worsen postpartum bleeding. First, the increased heart rate and cardiac output caused by anaemia could increase blood flow from bleeding vessels.Although the OR for a 10 g/L reduction in prebirth haemoglobin is smaller than for some other known risk factors for postpartum haemorrhage, because anaemia is a strong risk factor that is also highly prevalent worldwide, a substantial proportion of postpartum haemorrhage cases are likely to be due to anaemia. Nonetheless, anaemia was not recorded as the primary cause of postpartum haemorrhage in any of the 10 561 women in our study. Our results endorse the recommendation that every effort should be made to correct anaemia before delivery.