Low-birth-weight infants (< 2500 g) may result from pregnancies terminating before the completion of a normal gestational period (preterm infant) or from pregnancies during which the rate of intrauterine growth is abnormally slow, regardless of the duration of the gestation (SGA or small-for-gestational-age infant). Ever since the World Health Organization (1950) defined prematurity on the basis of birth weight (< 2500 g) alone, there has been slow but increasing recognition that a significant percentage of low-birth-weight infants are due to a decreased intrauterine growth rate rather than preterm delivery (Gruenwald, 1963).