Background: The new diagnostic criteria for gestational diabetes mellitus (GDM), proposed by the International Association of Diabetes and Pregnancy Study Groups in 2010, were recently accepted in Japan. Therefore, the frequency of GDM is four times higher than previously recorded. This means that GDM has become a more clinically important disease. This study aimed to assess how the number of patients with GDM as well as its complications have changed after adoption of the new criteria. Methods: A total of 3,610 pregnant women in the Japan Assessment of GDM Screening Trial and Okayama University Hospital were included. We analyzed the prevalence of GDM and its complications using the old and new criteria. Results: The prevalence of perinatal outcomes was increased by adopting the new criteria. There were many important perinatal complications in the additional new GDM criteria
therefore, patients with mild GDM, such as one-point disorder patients, should have careful interventions. Admission to the neonatal intensive care unit was significantly increased (p = 0.01) according to the new GDM criteria because the old criteria were stricter than the new ones. GDM patients with obesity (BMI ≥ 25 kg/m&lt
sup&gt
2&lt
/sup&gt
) had a high frequency of perinatal complications that could require active intervention and strict follow-up. Conclusions: Because the new GDM criteria greatly affect perinatal complications, intervention for GDM starting at an early stage and strict follow-up (especially GDM with obesity) are important for reducing complications as well as the incidence of diabetes and metabolic syndrome in the mother and child.