Association between lower fasting plasma glucose levels during oral glucose tolerance test and adverse perinatal outcomes: A Chinese cohort study

Background It is unknown whether fasting plasma glucose (FPG) level within the normal range as defined by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria is associated with perinatal outcomes. This study explored the associations between FPG levels lower than the IADPSG threshold during oral glucose tolerance test (OGTT) and adverse perinatal outcomes in women with or without gestational diabetes mellitus (GDM). Methods and findings From January 1, 2017, to May 31, 2022, this single-center retrospective cohort study included 33,417 women with singleton pregnancies at the Obstetrics and Gynecology Hospital of Fudan University, Shanghai, China. All women underwent a 75-g OGTT at 24–28 gestational weeks. The primary endpoint was a composite of adverse outcomes, including gestational hypertension, preeclampsia, fetal death and stillbirth, preterm birth, primary cesarean delivery, and small or large for gestational age. Overall, 3,108 (9.5%) women had IADPSG-defined GDM and of whom 2,426 (76.3%) had FPG levels below the IADPSG threshold. Compared to the GDM population, non-GDM women with borderline-normal FPG levels were at significantly greater risk of adverse outcomes with an adjusted odds ratio (aOR) of 1.62 (95% CI [1.20, 2.19]; p = 0.002) at 4.6 mmol/L, an aOR of 1.50 (95% CI [1.05, 2.13]; p = 0.025) at 4.8 mmol/L, and an aOR of 1.58 (95% CI [1.05, 2.40]; p = 0.030) at 4.9 mmol/L glucose level. Nonetheless, non-GDM women demonstrated significantly lower risk (aOR 0.66, 95% CI [0.44, 0.98]; p = 0.038) compared to GDM counterparts exhibiting low fasting glycemia at 3.9 mmol/L. However, this study was limited by its retrospective design and may lack generalizability to other ethnic groups. Conclusions Even at FPG levels lower than the IADPSG threshold, FPG was significantly associated with adverse perinatal outcomes, and the associations presented different patterns in women with and without GDM.