[Predictive models for ART]

A predictive model is a mathematical expression estimating the probability of pregnancy, by combining predictive variables, or indicators. Its development requires three successive phases: formulation of the model, its validation--internal then external--and the impact study. Its performance is assessed by its discrimination and its calibration. Numerous models were proposed, for spontaneous pregnancies, IUI and IVF, but with rather poor results, and their external validation was seldom carried out and was mainly inconclusive. The impact study-consisting in ascertaining whether their use improves medical practice--was exceptionally done. The ideal ART predictive model is a "Center specific" model, helping physicians to choose between abstention, IUI and IVF, by providing a reliable cumulative rate of pregnancy for each option. This tool would allow to rationalize the practices, by avoiding premature, late, or hopeless treatments. The model would also allow to compare the performances between ART Centers based on objective criteria. Today the best solution is to adjust the existing models to one's own practice, by considering models validated with variables describing the treated population, whilst adjusting the calculation to the Center's performances.