Objective Current standard of care in the United States uses a two-step screening and diagnosis approach for gestational diabetes mellitus (GDM). We aimed to assess the impact of the interval between screening and diagnosis on maternal and perinatal outcomes. Materials and Methods This is a retrospective cohort study of singleton pregnancies complicated by GDM at a single tertiary center from 2007 to 2013. Women were divided into three groups based on the interval between their screening and diagnostic tests: ≤ 7, 8 to 14, and > 14 days. Maternal outcomes were mode of delivery, White class A2GDM, and preeclampsia. Perinatal outcomes included preterm birth, birth weight, macrosomia, hypoglycemia, and birth injury. Results Chart review revealed 1,212 women with diagnosis of GDM and 565 were included in the analysis with 310 (55%) women ≤ 7 days, 149 (26%) women within 8 to 14 days, and 106 (19%) women > 14 days group. All maternal and perinatal outcomes were similar between groups including risk of cesarean delivery, A2GDM, preeclampsia, macrosomia, preterm birth, hypoglycemia, and birth injury. Conclusion Increasing time interval between screening and diagnosis may not negatively affect maternal or perinatal outcomes in pregnancies complicated by GDM.