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.

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 interventions. Expected 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 FGR.

Methods: A simulated dataset (n=1,005) utilized published mean fetal weight and TFLV references. Computer-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 TFLV. Estimated mortality probabilities and CDH severity were compared pre- and post-adjustment.

Results: Standard vs. corrected O/E TFLV means differed significantly (36.2% vs. 43.5 %) (p<0.001), as did corrected mortality probabilities (60.2% vs. 58.6 %) (p<0.001). CDH severity shifted: severe to moderate (17.1 %) and moderate to mild (8.6 %) with corrected O/E TFLV. Two-week corrections had greater impact than 1-week. Positive correlation existed between O/E TFLV and percent difference in values, while GA showed a negative correlation with the percent differences.

Conclusions: This simulation shows how using weight-adjusted GA norms affects O/E TFLV calculations. For fetuses with isolated CDH and FGR, adjusted GA increases O/E TFLV, reduces mortality estimates, and changes CDH severity classification, possibly affecting fetal intervention eligibility. Real patient studies are needed to confirm these findings.