A novel approach to calculating expected total fetal lung volume in fetuses with isolated congenital diaphragmatic hernia and fetal growth restriction: a theoretical computational simulation

Abstract

Objectives: Congenital diaphragmatic hernia (CDH) often coexists with fetal growth restriction (FGR)The observed-to-expected (O/E) total fetal lung volume (TFLV) is used to assess CDH severity, predict outcomes, and direct fetal interventionsExpected TFLV measurements traditionally rely only on gestation age (GA)This simulation assesses how incorporating weight-adjusted GA norms affects O/E TFLV calculations in patients with isolated CDH and FGRMethods: A simulated dataset (n=1,005) utilized published mean fetal weight and TFLV referencesComputer-generated variables included observed weights (3rd-10th %ile), O/E TFLV (10–65 %), and percent liver herniation (0–42 %)GA estimates were corrected by weight and used to calculate corrected O/E TFLVEstimated mortality probabilities and CDH severity were compared pre- and post-adjustmentResults: Standard vscorrected O/E TFLV means differed significantly (36.2% vs43.5 %) (p<0.001), as did corrected mortality probabilities (60.2% vs58.6 %) (p<0.001)CDH severity shifted: severe to moderate (17.1 %) and moderate to mild (8.6 %) with corrected O/E TFLVTwo-week corrections had greater impact than 1-weekPositive correlation existed between O/E TFLV and percent difference in values, while GA showed a negative correlation with the percent differencesConclusions: This simulation shows how using weight-adjusted GA norms affects O/E TFLV calculationsFor fetuses with isolated CDH and FGR, adjusted GA increases O/E TFLV, reduces mortality estimates, and changes CDH severity classification, possibly affecting fetal intervention eligibilityReal patient studies are needed to confirm these findings.