Abstract Body (Do not enter title and authors here): Background: Regionalization is the direction of patients to centers with appropriate levels of care and is key to optimizing outcomes. However, the role of prenatal care in perinatal regionalization for congenital heart defect (CHD) care is poorly understood.

Objective: To estimate associations between prenatal care initiation or visit frequency, and probability of delivery at a pediatric cardiac center.

Methods: Cross-sectional analysis of neonates with CHDs in Illinois, 2013-2021. Data were obtained from the Illinois Department of Public Health’s Adverse Pregnancy Outcomes Reporting System. The two exposure variables were: (1) prenatal care initiation – none vs. inadequate prenatal care (initiated after the fourth month or <50% of recommended visits); and (2) prenatal visit frequency – intermediate (50-79% of recommended visits) vs. adequate (80-109%) or adequate plus (> 110%) prenatal care. The outcome was delivery at a pediatric cardiac surgical center. Multivariable linear probability models estimating associations between both prenatal care exposures and delivery hospital, controlling for demographic and clinical characteristics, were stratified by CHD severity (mild, moderate, severe) to account for the modifying effect of CHD severity.

Results: Of 12,113 neonates with CHD, 25.4% were born at a cardiac center; 2.3% had no prenatal care, 13.4% had inadequate prenatal care, 10.8% had intermediate prenatal care, and 73.6% had adequate or adequate plus prenatal care; 13.0% had severe CHD and 73.0% had mild CHD. In multivariable models, prenatal care initiation was associated with a 10.5 percentage-point (pp) higher probability of delivery at a cardiac center for those with fetuses who had mild CHD (95%CI 4.7-16.2pp) and 30.2pp higher probability for severe CHD (95%CI 13.6-46.9pp). For mild CHD, adequate plus prenatal care was associated with a 6.7 pp (95%CI 4.0 to -9.4pp) lower probability of delivery at a cardiac center than intermediate prenatal care. Prenatal visit frequency was not associated with delivery at a cardiac center for severe CHD (Table 1).

Conclusion: Initiating prenatal care, even if delayed, is associated with a higher probability of delivery at a cardiac center, especially for severe CHDs. However, more prenatal visits may direct mild CHDs to non-cardiac centers. Both prenatal care components are crucial to achieve efficient perinatal regionalization of CHD care.