Background To determine a cutoff value for the 50-g glucose challenge test (50-g GCT) for the prediction of small-for-gestational-age (SGA) neonates. Methods This retrospective cohort study was conducted among pregnant women who were screened with the 50-g GCT at Hacettepe University Hospital between 1 January 2016 and 31 March 2019. Patients with 50-g GCT values <74 mg/dL (<10th percentile) served as the study group (n = 244), while patients with 50-g GCT values between 74 to 139 mg/dL served as the control group (n = 3104). Groups were compared in terms of demographic features, clinical characteristics, and obstetric outcomes. Logistic regression analysis was used to determine independent predictors of SGA. Receiver operating characteristic curves were used to assess the performance of 50-g GCT values in predicting SGA. Results Lower birthweight, birthweight percentile, and 5th-minute Apgar values, together with higher rates of SGA, were observed in the study group (P < .001 for all). A 50-g GCT value below the 10th percentile (odds ratio: 3.29, 95% CI: 2.31-4.69,P < .001) was a significant independent factor for SGA. A cutoff value of 89.5 mg/dL (84.9% sensitivity, 85.6% specificity) was determined for SGA. Conclusions Low 50-g GCT values (<89.5 mg/dL) may be an early indicator for SGA.