Difference in the prevalence of gestational diabetes mellitus according to gestational age at 75‐g oral glucose tolerance test in Japan: The Japan Assessment of Gestational Diabetes Mellitus Screening trial

AIMS/INTRODUCTION: To evaluate the differences in the results of 75‐g oral glucose tolerance tests (OGTTs) according to gestational age in Japan. MATERIALS AND METHODS: In this prospective cohort study, 2,578 pregnant women were divided into three categories based on their gestational age during the 75‐g OGTT: <14 weeks’ gestation, 14–23 weeks’ gestation and 24–32 weeks’ gestation. The association between gestational age and the results of the 75‐g OGTT were evaluated using multivariable analysis. RESULTS: Early gestational age was associated with high fasting plasma glucose levels at the time of the 75‐g OGTT, and low corresponding 1‐h and 2‐h plasma glucose levels. Compared with women with a gestational age of 24–32 weeks, women who had undergone the 75‐g OGTT at <14 weeks’ gestation had significantly higher odds of gestational diabetes mellitus diagnosis based on the currently used criteria in Japan (adjusted odds ratio 1.42, 95% confidence interval 1.07–1.90). CONCLUSIONS: The results of the 75‐g OGTT varied by gestational age. The use of the same 75‐g OGTT cut‐off values for the diagnosis of gestational diabetes mellitus, regardless of gestational age, might lead to increases in the prevalence of gestational diabetes mellitus diagnosis in Japan.