Comparison of fetal, newborn, and adult wound healing by histologic, enzyme-histochemical, and hydroxyproline determinations.

We compared simultaneous healing processes in fetal, newborn, and maternal rabbits using a miniaturized wound cylinder of expanded Gore-Tex tubing. The tubing was placed subcutaneously in fetal and maternal rabbits on day 23 of pregnancy (term = 31 to 32 days), and in 7-day-old newborn rabbits. At specific intervals, the tubing was removed and analyzed for hydroxyproline accumulation, histology, and cellular enzyme-histochemistry. Granulation tissue ingrowth and accumulation of hydroxyproline were each inversely related to age (fetus greater than newborn greater than maternal). The fetus showed an impressive infiltration of macrophages by day 4, fibroblasts by day 7, and a conspicuous lack of neutrophils in all specimens. Newborns and mothers had few cells until day 7, when a mixture of macrophages, neutrophils, and some fibroblasts appeared. We conclude that the fetus heals wounds rapidly by both mesenchymal cell proliferation and collagen deposition, and that these processes are more rapid in fetuses than in newborn or adult animals despite relative fetal hypoxemia.