To evaluate the value of fasting plasma glucose (FPG) value in the first prenatal visit to diagnose gestational diabetes mellitus (GDM). Medical records of 17,186 pregnant women attending prenatal clinics in 13 hospitals in China, including the Peking University First Hospital (PUFH), were examined. Patients with pre-GDM were excluded; data for FPG at the first prenatal visit and one-step GDM screening with 75-g oral glucose tolerance test (OGTT) performed between 24 and 28 weeks of gestation were collected and analyzed. The median ± SD FPG value was 4.58 ± 0.437. FPG decreased with increasing gestational age. FPG level at the first prenatal visit was strongly correlated with GDM diagnosed at 24-28 gestational weeks (χ(2) = 959.3, P < 0.001). The incidences of GDM were 37.0, 52.7, and 66.2%, respectively, for women with FPG at the first prenatal visit between 5.10 and 5.59, 5.60 and 6.09, and 6.10-6.99 mmol/L. The data of PUFH were not statistically different from other hospitals. Pregnant women (6.10 ≤ FPG < 7.00 mmol/L) should be considered and treated as GDM to improve outcomes; for women with FPG between 5.10 and 6.09 mmol/L, nutrition and exercise advice should be provided. An OGTT should be performed at 24-28 weeks to confirm or rule out GDM. Based on our data, we cannot support an FPG value ≥5.10 mmol/L at the first prenatal visit as the criterion for diagnosis of GDM.