[Predicting the risk of extra-uterine pregnancy. Construction and validation of a French risk scale]

This paper reports the construction and validation of a composite measurement scale to predict the risk of ectopic pregnancy in France. The data from three case-control studies of ectopic pregnancy conducted in France were used. Fourteen potential factors were found to be associated to ectopic pregnancy, which were grouped by multiple correspondence analysis in four dimensions: infection, pelvic surgery, smoking and induced conception. Logistic regression was further used to model the relationship between candidate risk factors (single or grouped as suggested by multiple correspondence analysis) and ectopic pregnancy. The regression coefficients of the final model were scaled and rounded to integers so as to make the scoring system simpler to use. The resulting composite measurement scale was finally validated on two independent samples. It allows simple determination (with a nomogram) of the absolute risk of developing ectopic pregnancy, for a given level of risk factors. This indicator for the risk of ectopic pregnancy could be used by clinicians to predict occurrence and provide an indication as to which type of early pregnancy follow-up and information should be given to women planning a pregnancy. It could also be used to provide earlier diagnostic screening in case of mild symptoms.