SummaryReference ranges for several haematology parameters in pregnancy were determined by the mathematical detection of Gaussian and Gamma distributions in partitioned but unselected patient data. For each trimester, red cell parameters were shown to be well described by Gaussian distributions. Platelet and white cell parameters were best described by Gamma distributions with the exception of eosinophil and basophil counts for which neither distribution was applicable. The reference ranges derived for each trimester are compared.