Abstract

Objectives: 1. Recognize the limitation of planning autologous breast fat grafting based solely on absolute injected volume. 2. Understand the injection-to-preoperative breast volume ratio (IPVR) as a baseline-adjusted index for estimating postoperative volumetric enlargement. 3. Apply the concept of diminishing returns at higher IPVR values to support more efficient fat utilization and treatment planning. Introduction: In autologous breast fat grafting, especially in lean patients with limited donor-fat reserves, overharvesting should be avoided. Planning based only on absolute injected volume may not reflect recipient-site capacity. We investigated whether the injection-to-preoperative breast volume ratio (IPVR) is associated with postoperative 3-dimensional volumetric enlargement and may support more efficient treatment planning. Materials / method: We retrospectively analyzed bilateral cases with preoperative and postoperative 3-dimensional volumetry and recorded total injected volume. IPVR was defined as total injected volume divided by preoperative bilateral breast volume. The primary time point was 3 months, with 6-month analysis as supportive. Primary endpoints were baseline-adjusted enlargement metrics, including relative volumetric gain and the final-to-preoperative volume ratio. Absolute volumetric gain and retention were also analyzed. Associations were assessed using Spearman correlation and linear and quadratic regression. Results: Complete 3-month data were available for 57 cases and 6-month data for 47. In the 3-month cohort, median preoperative bilateral volume was 224.7 mL, injected volume 500.0 mL, and IPVR 2.06. IPVR was associated with 3-month absolute volumetric gain (rho=0.287, p=0.030), but more strongly with relative volumetric enlargement (rho=0.883, p<0.001; linear R2=0.613). Quadratic regression improved model fit (R2=0.742; quadratic term p<0.001), suggesting diminishing returns at higher IPVR values. Conclusion: IPVR may be a practical planning index for estimating baseline-adjusted enlargement after autologous breast fat grafting. The observed non-linear relationship suggests that simply harvesting and injecting more fat may become less efficient at higher treatment intensities. IPVR may therefore support more efficient use of limited donor fat and help guide treatment planning.