The transverse rectus abdominis musculocutaneous (TRAM) flap, as the standard for breast reconstruction, can be performed in selected patients with operation scars in the abdomen. It is questioned why the unilateral TRAM flaps raised from the abdomen with scars seem to have more blood supply to the periphery. The effect of the abdominal midline incision on the survival of the TRAM flap was studied with the rat model. The survival of the inferiorly based unilateral TRAM flap was compared between a control group and three experimental groups in which initial abdominal midline incision was made 1, 2, or 4 weeks before TRAM flap elevation. The control group had a mean survival of 47.05 +/- 4.52% of their original flap surface area. The viabilities of the other groups were 72.19 +/- 11.05, 76.96 +/- 7.79, 90.26 +/- 3.67%, respectively. Results from all three groups were significantly higher than that of the control group. In the microangiogram of the TRAM flap, the main pedicle (deep epigastric system) and muscle perforators remained unchanged, but the subdermal plexus of the abdominal wall showed increase of size and density after incision. Histological examination also revealed corresponding findings. A midline incision in the abdomen, which was made at 1 or more weeks before unilateral TRAM flap formation, was found to improve the survival of the flap. These data may be explained by increase in the size and density of the subdermal plexus, which delivers the blood flow from the muscle perforators to the expanded area of abdominal wall. Therefore, the process of making the abdominal midline incision can be regarded as a minimal form of a prefabrication procedure, which is one of the well-known delay procedures.