The American Academy of Pediatrics [
3] and the Canadian Pediatric Society [
4] recommend that preterm infant growth should approximate intrauterine growth, with the argument that the fetus is not affected by extrauterine factors with negative impact on the nutrition status and growth, such as suboptimal nutrition support, major neonatal complications and medical interventions that increase energy expenditure and nutrient losses [
5]. However, the application of intrauterine growth rates to preterm infants in an extrauterine environment may be inadequate during the first postnatal weeks [
6] and even during the whole neonatal period. Loss of body water is an integral part of the physiology of postnatal adaptation and largely accounts for normal weight loss after birth [
7]. This does not occur in the fetus. Even providing the better current nutritional support to a “healthy” premature neonate, after normal body water loss has occurred, it is expected that a significant lag will be established between the rising extrauterine growth curve and the growth curve of a fetus of similar gestational age; in general, the postnatal weight curve will parallel and not exceed the intrauterine curve, maintaining the mentioned lag [
8]. Proposing the intrauterine growth as a goal for preterm infants may not be realistic and may be physiologically biased. This assumes that following the initial weight loss, the weight gain should reach the intrauterine growth curve reflecting a recovery of fat and muscle mass lost after birth, despite body weight loss in this period being predominantly due to physiologic extracellular water loss [
9]. Attempting to mimic intrauterine growth in early postnatal life may be achieved with excessive increase in fat mass, predisposing to obesity and late metabolic syndrome [
10]. Therefore, intrauterine growth data derived from cross-sectional measurements of birth weight overestimate postnatal growth, are not representative of the physiology of the neonates of the same corrected gestational age, and may not be ideal for monitoring growth and guiding nutritional support in preterm infants. At present, the available postnatal longitudinal growth charts for preterm infants are essentially a descriptive reference, accounting for the physiologic postnatal water loss, but influenced by nutrition practices contemporary to the construction of the charts, possibly outdated, as the 1999 Ehrenkranz chart [
8]. The new standards that are being developed by the International Fetal and Newborn Growth Consortium for the 21st Century study may provide better reference curves closer to standard, designed from longitudinal data of a selected population of preterm neonates with the lowest risk for factors known to affect prenatal or postnatal growth [
2].