Clinical significance of second-trimester 50-g glucose challenge test among Japanese women diagnosed as normoglycemic after first-trimester 75-g glucose tolerance test

Objective: This study was performed to determine how often Japanese women diagnosed as normoglycemic on first-trimester 75-g glucose tolerance test (75gGTT) later develop gestational diabetes mellitus (GDM). Material and methods: Sixty-two women with random plasma glucose (PG) level ≥ 105 mg/dL during the first trimester and subsequent first-trimester diagnosis of normoglycemia with 75gGTT underwent 50-g glucose challenge test (50gGCT) during the second trimester. Twenty-one with a positive 50gGCT result (60-m PG ≥ 140 mg/dL) underwent second-trimester 75gGTT. First-trimester random PG levels and 75gGTT results were compared between 21 and 41 women with positive and negative 50gGCT results, respectively. Changes in immunoreactive insulin (IRI) associated with 75gGTT were determined simultaneously. Results: All 21 women with a positive 50gGCT result showed normoglycemia on second-trimester 75gGTT. Thus, none of the 62 women developed GDM. Insulin resistance increased significantly in the 21 women with 75gGTT during the first and second trimesters, as indicated by increases in homeostasis model assessment for insulin resistance (HOMA-IR) and homeostasis model assessment for β-cell function (HOMA-β) with no significant changes in preload or afterload PG levels. Neither random PG levels (116 ± 12 vs. 116 ± 12 mg/dL, respectively) nor 75gGTT results (86 ± 6 vs. 84 ± 5 mg/dL for 0-minute [0-m] PG level, 130 ± 28 vs. 131 ± 25 mg/dL for 60-m PG, and 111 ± 19 vs. 118 ± 18 mg/dL for 120-m PG, respectively) during the first trimester differed significantly between the 41 and 21 women with negative and positive second-trimester 50gGCT results, respectively. Conclusion: Although insulin resistance increased in the second trimester, risk of developing GDM was < 1/62 among Japanese women in whom hyperglycemia was excluded with first-trimester GTT.