Predictive Value of Maternal HbA1c Levels for Fetal Hypertrophic Cardiomyopathy in Pregestational Diabetic Pregnancies

(1) Background: This study investigated the utility of first-visit HbA1c levels as a predictor of fetal hypertrophic cardiomyopathy (FHCM) in women with pregestational diabetes mellitus (PGDM). (2) Methods: A retrospective observational cohort study was conducted among all pregnant women with PGDM between 2012 and 2019. (3) Results: Of 329 participants, 5.8% had fetuses diagnosed with FHCM. These women exhibited significantly higher pregestational HbA1c (8.2% vs. 7.3%, <i>p</i> = 0.003) and higher first-visit HbA1c (7.6% vs. 6.9%, <i>p</i> = 0.001) and were less likely to have planned their pregnancies (<i>p</i> = 0.035). Fetuses with FHCM demonstrated a higher incidence of macrosomia (63.2% vs. 17.7%, <i>p</i> < 0.001; OR 9.20, 95% CI 3.31-25.58). Receiver-operating characteristic (ROC) analysis indicated an adequate predictive capacity for FHCM using first-visit HbA1c (AUC 0.75). An HbA1c threshold of 7.15% provided the best discriminative power, encompassing 38.9% of the cohort. (4) Conclusions: These findings underscore the value of assessing first-visit HbA1c levels for predicting FHCM in women with PGDM. The significant association between glycemic status and FHCM highlights the importance of optimizing glycemic control before and during pregnancy. Establishing optimal HbA1c cutoffs enables effective risk stratification and supports targeted clinical interventions.