Nutritional needs of the extremely low-birth-weight infant.

Abstract

0 ver 40 years ago, Dan& et al observed that the smaller, more immature newborn infant took longer to start postnatal growth, regain birthweight, achieve a normal rate of postnatal growth, and catch up in growth rate and size compared with larger, more mature infants.’ This was particularly true for those extremely lowbirth-weight infants (ELBW infants) weighing less than 1,000 g at birth, were born at gestational ages less than 27 to 28 weeks. These observations remain prophetic even today as shown in Fig 1, which compares nutrient intake and growth of a representative ELBW infant today with the “Dancis curves” of 1948; there has been little or no improvement in the onset and early growth of this group of infants. Why, in spite of vastly improved medical care of these infants and the provision of superior intravenous and alimentary formulas and supplemented milk, does this abnormal postnatal growth pattern persist? First, it may be that the advances in all aspects of neonatal care now produce surviving ELBW infants who are sicker and less physiologically stable, thus offsetting the beneficial effects of improved medical and specifically nutritional management. Second, we continue to be quite ignorant of how these babies grow at this early gestational age in utero, making it extremely difficult to know the physiologic basis of even normal in utero nutrition and growth. Third, what we do know of in utero nutrition, metabolism, and growth indicates that we still have very inadequate means of providing appropriate amounts and kinds of nutrients. Fourth, the vast array of growth factors, hormones, metabolic cofactors, etc. that are part of normal fetal nutrition, metabolism, and growth not only are not known or well understood but they are not provided as part of postnatal nutrition. Finally, the postnatal environment, the obligation to feed these infants postnatally by peripheral vein, central (but not portal) vein, and gut, plus the physiologically unstable condition of these infants make extrapolation from in utero conditions or from older more mature infants problematic at best, and frequently downright erroneous.2’3 Nevertheless, in 19’77 the American Academy of Pediatrics (AAP) stated that the major goal of nutrition of LBW, preterm infants should be “the optimal diet . . that supports a rate of growth approximating that of the third trimester of intrauterine life, without imposing stress on the developing metabolic and excretory systems.“4 Although important and attractive, this statement promotes an unfounded goal, and we still do not know if the achievement of this goal is good, let alone better than the growth rates more customarily seen. Furthermore, the AAP’s goal fails to address at least three important questions: (1) what are the nutritional requirements of these infants that contribute to the in utero growth; (2) what are the unique biologic and developmental features of these infants in utero with respect to body composition, growth rate, metabolic rate, and metabolic capacity; (3) what are the effects of postnatal medical conditions, environment, management practices, and nutritional practices on the metabolism and growth of these infants?