ABSTRACT Aims/Introduction We evaluated a simple diagnostic gestational diabetes mellitus (GDM) strategy (Japanese COVID‐19 GDM strategy) published by the Japanese Society of Diabetes and Pregnancy using GDM group data from the Diabetes and Pregnancy Outcomes for Mother and Baby (DREAMBee) study. Materials and Methods The study included 803 mothers with GDM diagnosed after 24 gestational weeks using an oral glucose tolerance test and 1,356 with normal glucose tolerance (NGT) from the DREMBee study. They were reclassified by the Japanese COVID‐19 GDM strategies (COVID‐19 GDM and COVID‐19 NGT) using glycated hemoglobin (HbA1c) and random plasma glucose or fasting plasma glucose (FPG) levels. We evaluated the usefulness of the Japanese COVID‐19 GDM strategy and investigated the parameters for diagnosing GDM managed with insulin therapy. Results Participants (n = 2,159) were assigned to COVID‐19 GDM (n = 413) and COVID‐19 NGT (n = 1,746) groups. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the Japanese COVID‐19 GDM strategy were 35.4, 90.5, 68.9, and 70.3%, respectively. When the risk factors for insulin therapy were analyzed using a regression model, HbA1c and FPG levels were risk factors for GDM with insulin therapy (P