UKOSS control data

While the population comparator data described above enabled adjustment for various socio-demographic and pregnancy related characteristics including socio-economic status, it did not include any information about the individual women's medical characteristics. A second comparator data set was assembled from control data previously collected for four separate United Kingdom Obstetric Surveillance System (UKOSS) studies on Seasonal Influenza (n = 694), Haemolysis, Elevated liver enzymes and Low platelet count (HELLP) (n = 488), Placenta Accreta (n = 266) and Sepsis (n = 762).²⁴ The UKOSS methodology is described in detail elsewhere.²⁵ Non-identifiable data are collected from all 194 consultant-led obstetric units in the UK each month, with a rigorous process to ensure a high level of data completeness. Participating hospitals selected control women as those who gave birth immediately before the index case with the condition under surveillance.