Association between area under the curve of oral glucose tolerance test and the risk of preterm birth among women with gestational diabetes mellitus: a mediation effect of gestational weight gain

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BACKGROUND: The risk of preterm birth (PTB) is associated with maternal hyperglycemia but differs by combinations of abnormal oral glucose tolerance test (OGTT) values. However, the potential pathway by which maternal hyperglycemia affects PTB is unclear. This study aimed to investigate the association between OGTT-related measures and PTB and evaluate the mediation effect of gestational weight gain (GWG) on the association between maternal hyperglycemia and the risk of PTB in women with gestational diabetes mellitus (GDM). METHODS: This retrospective cohort study included women with GDM from a women's and children's hospital in Chengdu, China, from December 2021 to December 2023. The associations between OGTT-related measures, GWG, and PTB were evaluated by logistic regression analyses. Two-step clustering was used to classify participants by area under the curve (AUC) of the OGTT. SPSS Process Macro was utilized to explore the mediation effect of GWG on the relationship between AUC and PTB. RESULTS: This study included 1860 women with GDM, of whom 694 (37.3%) women had higher AUC (≥ 17 mmol/L·h), 935 (50.3%) women had insufficient GWG, and 132 (7.1%) women had PTB. Multivariable logistic regression analyses showed that only higher AUC was associated with increased odds of PTB (OR:1.47, 95% CI:1.03 to 2.10; P = 0.036), and no significant associations between other OGTT-related measures and PTB were observed. Besides, GDM women with higher AUC had a higher risk of insufficient GWG (OR:1.23, 95% CI:1.02 to 1.49; P = 0.033), which was associated with increased odds of PTB (OR:2.15, 95% CI:1.47 to 3.14; P < 0.001). Mediation analyses revealed that the effect of AUC on PTB was mainly mediated through GWG (indirect effect: 0.15, bootstrapped 95% CI: 0.08 to 0.24). CONCLUSIONS: This study found that AUC of the OGTT was positively associated with the occurrence of PTB, and GWG mainly mediated this positive association. Effective intervention strategies for GDM should pay close attention to avoiding insufficient GWG when managing their blood glucose, especially for those with higher AUC levels, to reduce the impact of maternal hyperglycemia on the risk of PTB.

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