Introduction:Hypertrophic cardiomyopathy (HCM) is a known complication among infants of diabetic mothers (IDMs). Ventricular outflow tract obstruction is common in these newborns, often necessitating therapy with beta-blockers. Because of relatively small sample sizes, the in-hospital outcomes of IDMs with HCM are unknown.Hypothesis:HCM in IDM is associated with increased in-hospital mortality.Methods:We performed an analysis of all newborns with a diagnostic code for IDM admitted from 2004 to 2020 to one of the 49 children’s hospitals in the Pediatric Hospital Information System. Those with a diagnostic code for HCM were assigned to the HCM, and those without were assigned to the comparison group (No-HCM). Outcomes of interest included vasopressor use, cardiac arrest, use of extracorporeal membrane oxygenation (ECMO), length of stay, mechanical ventilation, and in-hospital mortality. Standard statistical techniques were used to assess differences between groups.Results:There were 37,085 IDMs (55% male) in the study cohort, 677 (1.8%) with a diagnosis of HCM. Prematurity was more common in No-HCM (43% versus 33%, p<0.001), and birthweight was lower in No-HCM (3.3 kg [IQR: 2.5-3.9] versus 4.0 kg [IQR: 3.4-4.6], p<0.001). HCM was twice as common in Black IDMs (3.1%) compared to White IDMs (1.6%)(p<0.001). As shown in the Table, HCM was associated with all study outcomes of interest.Conclusions:HCM is diagnosed twice as often in Black IDMs as White IDMs. HCM in IDMs is associated with multiple negative, in-hospital outcomes, including mortality. Further investigation is needed to determine if specific management strategies can ameliorate these negative outcomes.