Experimental Contributions to the Physiology of Fetal Macrosomia

The question whether a fetus in a normal pregnancy can be excessively nourished is biologically fundamental. It appears there is an upper limit of normal intrauterine growth which will be reached in the presence of optimal maternal nutrition (Hill, 1976). Excess maternal nutrition (for fetal needs) results in maternal obesity, but not fetal macrosomia. The biological mechanisms resulting in the prevention or restraint of excess fetal growth are not clear (Beard and Nathanielsz, 1976; Naftolin, 1978; CIBA Found. Symp., 1974). The need for such restraint is evident in polytoccus species. It is also evident in those species in which delivery is characterized by relatively close physical relationships between the dimensions of the fetal vertex, and the maternal pelvic inlet and birth canal. In support of the latter statement are the morbid consequences-increased incidence of prolonged labour and spontaneous birth trauma - in apparently normal newborns, of birth weight greater than two standard deviations from the mean.