Objective: Several circular RNAs are associated with important pathophysiological characteristics of gestational diabetes mellitus (GDM). This study intended to measure the expression of circ-PNPT1 in sera of GDM patients and to expound on its values on pregnancy outcomes. Methods: About 104 GDM patients and 71 healthy controls were recruited. The expression pattern of serum circ-PNPT1 was measured by reverse transcription-quantitative polymerase chain reaction. The diagnostic efficacy of circ-PNPT1 and fasting blood glucose (FBG) on GDM was evaluated by receiver operating characteristic (ROC) analysis. Parameters of glycolipid metabolism were determined using automatic biochemical analyzers. The correlation between circ-PNPT1 and glycolipid metabolism parameters was analyzed using Pearson analysis. GDM patients were divided into a high expression group and a low expression group based on the median value of circ-PNPT1 expression. Curves of adverse neonatal outcomes were drawn by Log Rank analysis. Results: GDM patients exhibited higher circ-PNPT1 expression than healthy controls. The area under the ROC curve of circ-PNPT1 diagnosing GDM was 0.9184 and the cut-off value was 1.435 (90.38% sensitivity, 85.92% specificity). Serum circ-PNPT1 expression was positively correlated with FBG, total cholesterol, and triglyceride in GDM patients. Neonates born to GDM patients with high circ-PNPT1 expression were prone to adverse outcomes. Conclusion: Circ-PNPT1 was highly-expressed in the sera of GDM patients. Circ-PNPT1 affected glycolipid metabolism and its expression had certain reference values on adverse pregnancy outcomes.