The PIERS model was developed and validated in 8 tertiary perinatal units,
internationally. It is intended for use by clinicians as a tool to stratify risk
for adverse maternal outcomes within 48hrs of admission to hospital with pre-eclampsia.
For the purpose of the model, pre-eclampsia is defined as:
i) blood pressure (BP) ≥140/90mmHg (at least one component, twice, ≥4hr apart,
after 20 weeks’ gestation) and either proteinuria (≥2+ by dipstick, ≥0.3g/d by 24hr urine collection, or ≥30mg/mmol by spot urinary
protein : creatinine ratio) or hyperuricaemia (greater than local upper limit of
normal for non-pregnancy), or
ii) HELLP syndrome (haemolysis, elevated liver enzymes and low platelet
syndrome) even in the absence of hypertension or proteinuria, or
iii) superimposed pre-eclampsia, defined as pre-existing hypertension with
accelerated hypertension, new proteinuria, or new
This model has been developed and initially validated but further external validation is required. This model is not meant to replace routine clinical assessment and surveillance strategies, and should be used with caution. For more information on the development of the model and its use, please read the outcome definition, and
the full description of statistical methods hosted on this website.
The tool below utilizes the PIERS model to calculate the probability of adverse
maternal outcomes. For information on the PIERS model, please