Predictive value of a screen for gestational diabetes mellitus:: influence of associated risk factors

Background There is a need for solid evidence of the relative advantages of universal vs. selective screening for gestational diabetes mellitus. Our study of a broad obstetric population determines the positive predictive value of the 50-g oral glucose challenge test for screening in the presence and absence of classical gestational diabetes risk factors. Methods. A retrospective cohort study was carried out with a total of 2,574 pregnant women. Clinical information was obtained from hospital records and each patient's medical history, and gestational diabetes risk factors were quantified for each pregnant woman. The positive predictive value of a screen was determined with respect to the number of risk factors. Results. Age 30 or over, family history of diabetes, obesity (BMI greater than or equal to 27) and previous fetal macrosomia were established as the most frequent risk factors. Just over half (54.2%) of our population presented one or more risk factors. Screening covered 75% of the population, and was positive in 15% of the cases. Diagnosis was confirmed in 64 cases, 57 of them at risk, and seven with no risk Factors. We obtained an overall positive predictive value of 21.8% (CI 17.3-27.0). This figure increases with the number of risk factors, from 12% for the women with no risk factors, to 40% for those presenting three or more risk factors. Conclusions. A selective screening program that takes into account the clinical background and characteristics of each pregnant woman allows a high yield of true positives while reducing the possible undesirable effects associated with false positives.