AbstractGestational diabetes mellitus (GDM) is defined as carbohydrate intolerance during pregnancy. In Denmark the health service offers selective screening for GDM, i.e., admission to an oral glucose tolerance test (OGTT) after pre-screening with interview for clinical risk factors for GDM, two capillary fasting blood glucose (cFBG) measurements and a urine test for glucosuria. The aim of the present study was to investigate the power of the pre-screening to identify GDM and the screening to predict adverse clinical outcome.A retrospective investigation of pregnant women undergoing screening during 1998 at Vejle County Hospital, Denmark was undertaken. The two most frequent pre-screening criteria for OGTT were body-mass index (BMI) ≥ 27 kg/mThe frequency of complicated delivery was similar in GDM (58%) compared to non-GDM (56%). The best predictor of complicated delivery was a BMI with OR=1.50 (95% CI: 0.87 to 2.60) for BMI ≥ 27 kg/mScreening cFBG of 4.1 mmol/l was unable to predict GDM and adverse outcome. Glucosuria was too rare to be effective as a screening tool. Pre-screening did not identify GDM. The best predictor of complicated delivery was a high BMI. The best predictor of foetal adverse outcome was cBG