Simple and generalizable formula for predicting deep inferior epigastric artery perforator flap weight in breast reconstruction.

[BACKGROUND] Prediction of flap weight is valuable for surgical planning when using a deep inferior epigastric artery perforator (DIEP) flap for breast reconstruction and may reduce donor site morbidity and perfusion-related problems. The aim of this research was to develop a simple and generalizable formula for predicting DIEP flap weight.

[METHODS] We retrospectively reviewed 100 patients who underwent breast reconstruction with a DIEP flap at our institution between November 2018 and July 2025. We developed the following formula: predicted flap weight = α × W × H × T, where W and H denote flap width and height, T denotes subcutaneous thickness, and α is a coefficient specific to each flap design. The relationship between the WHT value and actual flap weight was assessed using the Pearson correlation coefficient. Prediction accuracy was evaluated by K-fold cross-validation. The number of folds was varied to examine the relationship between the number of training cases and prediction accuracy. Multivariate analysis was performed to identify factors associated with estimation error.

[RESULTS] The Pearson correlation coefficient was 0.964. The mean absolute percentage error was 12.7% when using 5 cases to estimate the coefficient, 12.3% when using 10 cases, and 12.2% when using 20 cases. Multivariate analysis revealed that thinner subcutaneous tissue significantly increased the estimation error (P = 0.01).

[CONCLUSIONS] This formula demonstrated excellent accuracy, requiring only a simple measurement in a small sample. This approach is practical and generalizable for preoperative planning of breast reconstruction using a DIEP flap and is broadly applicable across institutions and flap designs.