The flat glucose response curve during oral glucose tolerance tests in Chinese pregnant women and its association with adverse outcomes.

Introduction: Flat glucose response curves observed during the oral glucose tolerance test (OGTT) in pregnant women are relatively prevalent. This study aimed to investigate the characteristics and perinatal outcomes of Chinese women who presented with flat OGTT curves during pregnancy.

Material and methods: A total of 23 576 pregnant women without gestational diabetes mellitus (GDM) were recruited into this study. They were classified into two groups according to the shape of their glucose response curves obtained from OGTTs performed at 24-28 weeks of gestation. The curves were categorized as either flat or normal. Specifically, a flat curve was defined as a less than 16.5% increase in plasma glucose levels during the OGTT, while all other curves were regarded as normal. Logistic regression analysis was employed to examine the associations between these curve types and the risk of perinatal outcomes. Additionally, these relationships were evaluated across different maternal age groups and preconception body mass index (BMI) categories.

Results: Among the participants, 932 (3.95%) displayed a flat curve, while 22 644 (96.05%) showed a normal curve. Women with a flat curve were significantly younger (p < 0.001) and had a lower BMI (p < 0.001). Compared with those with a normal curve, women with a flat curve had lower incidences of gestational hypertension and preeclampsia. Additionally, neonates born to mothers with a flat curve had lower birth weights and lower occurrences of large for gestational age (LGA) and macrosomia. Logistic regression analyses, using the normal-curve group as the reference, demonstrated that, regardless of confounder adjustments, the flat-curve group was associated with a protective effect against gestational hypertension, preeclampsia, LGA, and macrosomia development (all p < 0.05). Moreover, these risks differed according to maternal age and preconception BMI. No significant differences were observed in other maternal or neonatal outcomes.

Conclusions: A flat OGTT curve is associated with lower birth weight and reduced risks of LGA, macrosomia, gestational hypertension, and preeclampsia. Identifying the flat curve as a protective factor for LGA, macrosomia, gestational hypertension, and preeclampsia, particularly among women with different maternal ages and preconception BMIs, may facilitate personalized risk assessment and management.