The PIERS (Pre-eclampsia Integrated Estimate of RiSk) model : development of a valid outcome prediction model for pre-eclampsia

Objective: This research responded to the need to define evidence-based criteria of maternal risk by developing a model - the Pre-eclampsia Integrated Estimate of RiSk (or PIERS) model – that predicts a combined adverse maternal outcome (mortality and/or significant morbidities) within 48 hour of, and up to seven days after, admission with pre-eclampsia (study eligibility). Methods: Prospective data for this project came from the PIERS study database (1259 women, seven international tertiary centers, 4 year period). Part 1. Using PIERS data and retrospective data from BC Women’s Hospital, the impact of standardized assessment and surveillance (standing orders) on the incidence of adverse maternal outcomes was assessed. Part 2. Criteria of ‘severe’ disease were assessed against their ability to identify maternal risk. Part 3. For PIERS model development and initial validation, independent predictor variables were selected through univariable logistic regression and tests of correlation and co-linearity. The fitted models were derived using multivariate logistic regression, predictive performance evaluated using area under the receiver-operator curve [AUC], and initial validation by cross-validation. Results: Part 1. Introducing standing orders reduced the incidence of adverse maternal outcomes (5.1% to 0.7%; OR 0.14 [0.04, 0.49]). Part 2. Most Canadian and American severity criteria did not predict adverse outcomes. Part 3. Two PIERS outcome prediction models were developed and initially validated. The fullPIERS model (AUC 0.906 [0.851, 0.961]), for use in well-resourced settings, comprises six independent clinical and laboratory variables. The miniPIERS model (AUC 0.817 [0.738, 0.896]), for use in minimally-resourced settings, comprises three independent clinical variables. Both models (fitted and cross-validated) maintain AUC>0.7 up to seven days after eligibility. Conclusion: Standardized assessment and surveillance of women with pre-eclampsia reduces maternal risks. Published criteria of ‘severe’ disease do not denote increased maternal risk. The two pre-eclampsia-specific outcome prediction models, fullPIERS and miniPIERS, identify maternal risk up to 7 days before complications arise.