Protocol for the development and validation of a risk prediction model for stillbirths from 35 weeks gestation in Australia
Abstract Background Despite advances in the care of women and their babies in the past century, an estimated 1.7 million babies are born still each year throughout the world. A robust method to estimate a pregnant woman’s individualized risk of late-pregnancy stillbirth is needed to inform decision-making around timing of birth to reduce the risk of stillbirth from 35 weeks gestation. Methods This is a protocol for a retrospective cohort study of all late-pregnancy births in Australia (1998-2015) from 35 weeks gestation including 7,200 stillbirths among 4.9 million births at an estimated rate of 1.47 stillbirths per 1000 live births. A multivariable logistic regression model will be developed in line with current T ransparent R eporting of a multivariable prediction model for I ndividual P rognosis or D iagnosis (TRIPOD) guidelines to estimate the gestation-specific probability of stillbirth with prediction intervals. Candidate predictors were identified from systematic reviews and clinical consultation and will be assessed through univariate regression analysis. To generate a final model, elimination by backward stepwise logistic regression will be performed. The model will be internally validated using K-fold cross-validation and externally validated using a geographically unique dataset. Overall model performance will be assessed with R 2 in addition calibration and discrimination. Calibration will be visualized using a calibration plot. Discrimination will be measured by the C- statistic and visualized using area underneath the receiver-operator curves (AUROC). Clinical usefulness will be reported as positive and negative predictive values and a decision curve analysis will be considered. Discussion A robust method to predict a pregnant woman’s individualized risk of late-pregnancy stillbirth is needed to inform timely, appropriate care to reduce stillbirth. Among existing prediction models designed for obstetric use, few have been subject to internal and external validation and many fail to meet recommended reporting standards. In developing a risk prediction model for late-gestation stillbirth with both providers and pregnant women in mind, we endeavor to develop a validated model for clinical use in Australia that meets current reporting standards.