Predicting cup size after reduction mammaplasty

Presently, predicting cup size after reduction mammaplasty is largely based on experience. Regnault and Daniel (1984) proposed a formula for estimating the appropriate weight of reduction to achieve a desired cup size. To validate their method, we studied 75 consecutive patients undergoing bilateral breast reduction mammaplasty. Patients were measured pre-operatively and 6 weeks post-operatively using two techniques to determine bra size. Actual weight of breast tissue excised was compared to the predicted values using the Regnault and Daniel formula for each measuring technique (Methods A and B). A modified formula (Method C) was developed to increase the accuracy. The results obtained using Methods A and B were compared with those of Method C. A paired sample t test showed no significant difference between actual and predicted weight of reduction for using Method A or C. Method B systematically underestimated the weight of tissue to be removed. The mean estimate for Method B was 730 g, a difference of -45 g (CI: -81.7 to -8.9; p = 0.015). For Method A, the mean was 765.5 g, a difference of 9.4 g (CI: -68.1 to 49.3; p = 0.75). This compared to Method C where the mean predicted weight of tissue to be removed was 770.4 g, a difference of -4.5 g (95% CI: -42.4 to 33.4; p = 0.81). The implications of these findings are discussed.