AbstractIn 1984, Peter Dunn postulated that infants from 28 weeks ‘gestation till 18 weeks’ postnatal age who grow normally have almost identical potential growth velocities, regardless of racial and geographic differences. He suggested that the straight line growth curve in this period could be used as a perinatal growth chart for international reference. We composed biological growth curves for Japanese fetuses by eliminating data with risk factors for fetal growth, and compared them with the curves of Dunn. Our conclusions are as follows:1) Japanese population fetal growth curves correspond with the curve of Dunn between 28 and 38 weeks' gestation.2) Even in ideal conditions, flattening of fetal growth after 38 weeks' gestation always occurs.3) In the early postnatal period, infants grow with the same straight line velocity as during fetal growth between 28–38 weeks' gestation. Infants from 28 weeks' gestation to 18 weeks' postnatal age have an almost identical growth potential in spite of some degree of growth constraint in utero after 38 weeks' gest