Hospital departments, where the births had taken
place, were asked to provide copies of antenatal charts
and hospital discharge codes. The antenatal charts
include data on presence of increased urinary protein
level and blood pressure measurements at the various
pregnancy visits. Using this hospital-derived information
as the gold standard, the positive predictive value
(PPV) of a pre-eclampsia diagnosis in MBRN was
found to be 83.9% [26]. The PPV was higher for
primiparous women. This result indicates that there is
an element of misclassification of pre-eclampsia in
papers that only use the MBRN diagnosis. To the
extent that this is non-differential with respect to other
variables that are studied, it will tend to weaken the
estimated association measures.