Abstract Body (Do not enter title and authors here): Background: Newborns with d-transposition of the great arteries (d-TGA) often require an urgent balloon atrial septostomy (BAS) immediately after birth, which can be challenging to predict. As such, cardiac centers, especially those without in-house delivery, should plan for immediate transport and cardiac intervention. The objective of this study was to evaluate the impact of risk stratification on both transport times to the cardiac intensive care unit (CICU) and to BAS in the d-TGA population.

Methods: A retrospective analysis was performed on all fetuses with d-TGA and an intact ventricular septum born between 1/1/2013 and 12/31/2023. Fetuses born before 2018 were not risk stratified or assigned a level of care (LOC) assignment. Fetuses born after 2018 were assigned either a moderate risk of hemodynamic instability (LOC 3) or high risk of hemodynamic instability (LOC 4), based on findings on fetal echocardiography (FE) associated with increased risk for urgent BAS. Primary outcomes were times from birth to CICU arrival and from birth to BAS. A BAS was considered urgent if completed within 2 hours of CICU arrival. A BAS was excluded if performed greater than 48 hours after birth. Statistical analyses compared time-based outcomes among pre-LOC and post-LOC fetuses (stratified as either LOC 3 or 4).

Results: A total of 81 newborns with a prenatal diagnosis of d-TGA were analyzed. Fetuses assigned an LOC had a lower time between birth and CICU arrival compared to fetuses with d-TGA who were not risk stratified (p=0.012) (Table 1). There were no differences in times from birth to BAS or from CICU arrival to BAS for pre- or post-LOC groups.

Conclusion: Implementation of risk stratification for d-TGA fetuses can help decrease time between birth and arrival to the CICU. Risk stratification and appropriate delivery planning should be considered, especially at centers without in-house delivery. Although risk stratification alone does not shorten time to cardiac intervention, further research is needed to determine if other prenatal characteristics may predict which patients will require an urgent BAS.