Glycosylated Hemoglobin Levels in the Third Trimester for Predicting Adverse Pregnancy and Neonatal Outcomes in Women with Pre-Gestational Diabetes: A Multi-Center Retrospective Cohort Study in South Korea

<b>Background/Objectives</b>: The objective of this study is to investigate pregnancy and neonatal outcomes in women with pre-gestational diabetes (PGDM) in the Korean population and compare outcomes according to glycosylated hemoglobin (HbA1c) levels in the third trimester. <b>Methods</b>: Singleton pregnant women with PGDM, with follow-up data, and who delivered at 16 Korean tertiary institutions between 2010 and 2023 were included for analysis. Eligible patients were divided into two groups according to HbA1c levels (47.5 mmol/mol, 6.5%) in the third trimester (well-controlled and poorly controlled group). Adverse pregnancy and neonatal outcomes between the two groups were compared. The primary outcome was the composite neonatal adverse outcome and the secondary outcome was pregnancy-related hypertension. <b>Results</b>: In 416 pregnancies, the mean HbA1c in the third trimester was 45 mmol/mol (6.26%). Of these, 296 (71.2%) women were included in the well-controlled group and 120 (28.8%) in the poorly controlled group. Between these, the poorly controlled group showed a significantly higher risk of composite neonatal adverse outcome (57.8% vs. 79.2%, <i>p</i> < 0.001) and pregnancy-related hypertension (14.5% vs. 24.2%, <i>p</i> = 0.022). In multivariate analysis, HbA1c > 6.5% in the third trimester was associated with higher risk of composite neonatal adverse outcome and pregnancy-related hypertension. HbA1c ROC curves for the third trimester that predicted composite neonatal adverse outcomes had an AUC of 0.66; HbA1c of 43.7 mmol/mol (6.15%) had a sensitivity of 52.3% and specificity of 73.5% (<i>p</i> < 0.001). <b>Conclusions</b>: In PGDM, HbA1c > 47.5 mmol/mol (6.5%) in the third trimester was significantly associated with a higher risk of adverse neonatal and pregnancy outcomes and could be a predictive factor for composite neonatal adverse outcomes and pregnancy-related hypertension. Maintenance of HbA1c levels below 43.7 mmol/mol (6.15%) in the third trimester might decrease the risk of adverse neonatal outcomes.