How long do preconception risk prediction models hold? Influence of selective fertility on model performance

van Kuijk SMJ, Sep SJS, Nelemans PJ, Smits LJM. How long do preconception risk prediction models hold? Influence of selective fertility on model performance. Paediatric and Perinatal Epidemiology 2010; 24: 602-607. Risk estimates derived from preconception prediction models can be used to counsel women with regard to any future pregnancies. Women with a high predicted risk of an adverse pregnancy outcome may decide more frequently not to try for another pregnancy than women with a low predicted risk. This prediction-guided selective fertility can cause a change in the composition of the pregnant population with respect to those parameters that are included in the prediction model. The question is whether such a change in composition could influence the performance parameters of the prediction model, such as sensitivity, specificity, positive and negative predictive values as well as the discriminative ability, when evaluating risks in the new population and whether it could compromise the longevity of the model. Using a hypothetical example, we show that the original sensitivity and specificity estimates of a preconception prediction model for an adverse pregnancy outcome no longer hold when the model is applied to a population affected by model-based selective fertility: sensitivity decreases, while specificity increases. However, individual patient risk estimates remain unbiased and discriminative ability, expressed as the area under the receiver operating characteristic curve, remains unaffected.