Abstract Body (Do not enter title and authors here): Introduction: Prenatal diagnosis of coarctation of the aorta (COA) is challenging and associated with high false positive rates. Postnatal confirmation of the diagnosis is frequently not possible until after closure of the ductus arteriosus, often days after birth. During this period, neonates with prenatal diagnosis of COA undergo an ‘arch watch,’ which may include invasive procedures, laboratory draws, and repeated imaging studies. Historically, over half of these neonates are deemed to have no heart disease.

Hypothesis: We sought to characterize the clinical implications of prenatal overdiagnosis of COA. We hypothesized that newborns with false positive prenatal diagnosis of COA undergo increased testing and extended hospitalizations after birth.

Methods: Term neonates with prenatal diagnosis of COA +/- ventricular septal defect born at our quaternary care center between 2005 and 2024 were identified in the electronic medical record. Patients were excluded if they had more complex heart disease, extracardiac anomalies, or known genetic abnormalities. Data were collected from the time of maternal fetal cardiology consultation through neonatal cardiac repair or hospital discharge if repair was not required. Descriptive statistics were performed and reported as n (%) and median (Q1,Q3).

Results: Of 107 term neonates identified who underwent an arch watch, 72 (67%) did not require surgery. Among those not requiring repair, median length of stay was 3 days (2, 7). Twenty-six neonates (36%) had ≥3 echocardiograms, median time to first echocardiogram was 1 hour (1,2), and the ductus arteriosus was more than moderate in size on the first study in 40 neonates (56%). Twenty-four neonates (33%) had umbilical lines placed, 39 (54%) had X-rays, 35 (49%) had non-routine laboratory workup in the first 12 hours of life, and 45 (62.5%) had genetic testing.

Conclusions: The majority of newborns who underwent an arch watch did not require COA surgery, yet they were subjected to cascading neonatal cardiac critical care including umbilical line placement, multiple echocardiograms, and laboratory and radiographic testing. Our study reveals that the majority of infants who underwent a negative arch watch had genetic testing performed. More tailored perinatal care, with risk-stratified pathways incorporating delay of potentially risky procedures until confirmation of diagnosis, may reduce the clinical burden on patients who are eventually cleared of the prenatal diagnosis of COA.