Fig. 2: Subgroup analysis of hemodynamic screening target neonatal echocardiograms (TNE) performed in infants born at ≤26 6/7 weeks’ gestation without congenital heart disease at the University of Iowa NICU (January 2019–June 2025).

The first column shows classification based on ductal diameter alone (<1.5 mm vs ≥1.5 mm vs no PDA). The second column reflects categorization using the Iowa PDA severity score at 18–24 postnatal hours, and the third column depicts reclassification over the first 7 postnatal days. Flow widths represent the number of infants transitioning between categories. Colors correspond to baseline shunt volume severity (blue: no PDA; orange: low volume shunt; green: moderate–high volume shunt for which medical therapy is recommended; red: supportive physiology such as pulmonary hypertension or heart dysfunction). “Others” represents infants who could not be assigned to a single category by day 7 because of premature death, absence of a repeat TNE assessment, or multiple varying physiologies across the first week. This analysis highlights the heterogeneity of early PDA physiology and the dynamic evolution of ductal significance in the first postnatal week.