Prevention of postpartum haemorrhage: a distributional approach for analysis

Background There is empirical evidence that measured postpartum blood loss has a lognormal distribution. This feature can be used to analyze events of the type ‘blood loss greater than a certain cutoff point’ using a lognormal approach, which takes into account all the quantitative observations, as opposed to dichotomizing the variable blood loss volume into two categories. This lognormal approach uses all the information contained in the data and is expected to provide more efficient estimates of proportions and relative risk when comparing treatments to prevent postpartum haemorrhage. As a consequence, sample size can be reduced in clinical trials, while keeping the statistical precision requirements.