Screening or diagnostic: Markedly elevated glucose loading test and perinatal outcomes

Objective. To determine the diagnostic value of markedly elevated 50-g glucose loading test results (≥200 mg/dL) and associated perinatal outcomes. Method. This was a retrospective cohort study of 14 771 pregnancies screened for gestational diabetes mellitus (GDM) between 1988 and 2001. The positive predictive value of the 50-g oral glucose loading test (GLT) results as measured by plasma glucose value was examined. Perinatal outcomes were assessed for women with GLT results ≥200 mg/dL compared to GLT <200 mg/dL, stratified by the diagnosis of GDM. Statistical comparisons were made using the Chi-square test and Student's t-test and potential confounding factors were controlled for using multivariable logistic regression analyses. A p value <0.05 and 95% confidence intervals were used to indicate statistical significance. Results. The positive predictive values for a GDM diagnosis were 62% for GLT results between 180 and 189 mg/dL, 79% for those between 200 and 209 mg/dL, and 100% for GLT results ≥230 mg/dL. Compared to women with a GLT result <200 mg/dL, among women not diagnosed with GDM but with a GLT ≥200 mg/dL the adjusted odds ratio (aOR) for cesarean delivery was 4.18 (95% confidence intervals, 1.15-15.2). These women also had higher aORs for preterm delivery <32 weeks (aOR = 8.05 (1.02-63.6)), shoulder dystocia (aOR = 15.14 (1.64-140)), and their neonates were more likely to have a 5-minute Apgar score <7 (aOR = 6.41 (1.23-33.3)). For women diagnosed with GDM and with a GLT ≥200 mg/dL, the aOR for cesarean delivery was also elevated compared to those with a GLT <200 mg/dL (aOR = 2.24 (1.19-4.21)). Conclusion. A GLT value of ≥200 mg/dL is not absolutely diagnostic for gestational diabetes but is associated with unfavorable perinatal outcomes.