[Validity of self-reported gestational diabetes mellitus in the immediate postpartum]

Studies based on self-reporting of risk factors or morbidity are useful in public health, due mainly to the low cost and ease of data collection, but the accuracy of the resulting data is important for the internal validity of the research. The aim of this study was to evaluate the agreement between self-reported gestational diabetes mellitus and prenatal care medical records (gold standard). Agreement was measured by sensitivity, specificity, accuracy, kappa statistic, and confidence intervals (95%CI). From July to December 2007, all the women who gave birth in three maternity hospitals in Pelotas, Rio Grande do Sul, Brazil, were visited in the immediate postpartum. 1,047 women were interviewed, of whom 872 were in possession of their prenatal care card; of these, 869 had their blood glucose recorded on the card. Mean age was 26.7 years. Prevalence of gestational diabetes mellitus based on the gold standard was 4.3% (95%CI: 3.0-5.8), while the self-reported rate was 4% (95%CI: 2.8-5.5). Sensitivity of self-reported gestational diabetes mellitus was 72.9% (95%CI: 55.9-86.2); specificity was 99% (95%CI: 98.1-99.6); accuracy 97.9% (95%CI: 96.7-98.7); kappa 74%. For this population, self-reported gestational diabetes mellitus is valid information and can be used in population-based studies.