Gestational diabetes mellitus (GDM) is defined as a carbohydrate intolerance with onset or first recognition occurring during pregnancy and GDM could be risk factor for various maternal fetal complications. This study aimed to investigate risks of maternal and neonatal outcomes according to GDM and normal glucose tolerance. This retrospective, observational study included singleton pregnant women who had received a 50-g oral glucose challenge test in 2nd trimester of gestation and gave birth at National Health Insurance Service Ilsan Hospital. Maternal and neonatal complications were compared between GDM and non-GDM groups. Among the 682 women, 56 were diagnosed with GDM and 626 were non-GDM group. Maternal age was older and prepregnant body mass index was higher in GDM. The rate of cesarean delivery, preeclampsia, and transfusion was similar; however, the incidence of preterm birth was higher in GDM. Multivariate analysis, however, showed that GDM was independent risk factor only for preterm birth in <37 weeks (adjusted odds ratio, 2.25; 95% confidence interval, 1.16-4.36). Regarding neonatal morbidities, APGAR score <7 at 5 minutes and the rate of macrosomia were similar; however, the rates of neonatal intensive care unit (NICU) admission, large for gestational age (LGA), and intubation were higher in GDM. Multivariate analysis, however, showed that GDM was not independent risk factor for LGA, NICU admission, and intubation rate. Compared with the non-GDM group, GDM was associated with an increased likelihood of preterm birth <37 weeks, however, did not increase cesarean delivery, postpartum hemorrhage, LGA, and NICU admission rate. This study showed that the majority of women with GDM delivered with similar maternal and neonatal outcomes in non-GDM women.