Physiological adjustment to postnatal growth trajectories in healthy preterm infants

Abstract

Background: International guidelines suggest that growth of preterm infants should match intrauterine rates. However, the trajectory for extrauterine growth may deviate from the birth percentile due to an irreversible, physiological loss of extracellular fluid during postnatal adaptation to extrauterine conditions. To which "new" physiological growth trajectory preterm infants should adjust to after completed postnatal adaptation is unknown. This study analyzes the postnatal growth trajectories of healthy preterm infants using prospective criteria defining minimal support, as a model for physiological adaptation. Methods: International, multi-center, longitudinal, observational study at five neonatal intensive care units (NICUs). Daily weights until day of life (DoL) 21 of infants with undisturbed postnatal adaptation were analyzed (gestational ages: (i) 25-29 wk, (ii) 30-34 wk). results: 981 out of 3,703 admitted infants included. Maximum weight loss was 11% (i) and 7% (ii) by DoL 5, birth weight regained by DoL 15 (i) and 13 (ii). Infants transitioned to growth trajectories parallel to Fenton chart percentiles, 0.8 z-scores below their birth percentiles. The new trajectory after completed postnatal adaptation could be predicted for DoL 21 with R 2 = 0.96. conclusion: This study provides a robust estimate for physiological growth trajectories of infants after undisturbed postnatal adaptation. In the future, the concept of a target postnatal trajectory during NICU care may be useful. i mproved survival rates of very-low-birth-weight (<1,500 g birth weight) infants have shifted the focus of neonatal care onto improving postnatal growth and nutrition, aiming to achieve growth rates that optimize later health outcomes (1). Pediatric societies in North America and Europe have recommended that postnatal growth of preterm infants match the in utero growth rates of fetuses that remain in utero until full-term (2-4). These recommendations gain importance in light of the Developmental Origins of Health and Disease (DOHaD) hypothesis (5). The DOHaD concept suggests that suboptimal growth of a fetus or a newborn infant can impact the early onset of adult metabolic and cardiovascular diseases. In utero, the growth rate of an individual fetus is determined by its genetic potential and modified by "environmental" factors such as maternal nutrition, body composition, pathologies, or altitude above sea level. After birth, growth patterns of preterm infants are under external control by neonatal staff who modify the infants' nutrient intake. Figure 1 shows three hypothetical postnatal trajectories for a given preterm infant (27 wk of gestation, birth weight 1,000 g). It is of interest to note that these trajectories have similar slopes and hence not dramatically different growth rates. However, postnatal adjustment to different percentiles during the phase of stable growth will lead to different body compositions-potentially affecting later health outcomes.The current evidence for optimal postnatal growth trajectories is scarce....

Improving Growth for Infants ≤1250 Grams Receiving an Exclusive Human Milk Diet

“…Although previously the stated goal for weight gain in the NICU was to achieve intrauterine growth velocities using calculations from standardized growth curves of preterm infants based on cross‐sectional data from infants born at various gestational ages, a recent review of evidence to support nutrition practice guidelines has questioned this approach . It has been suggested that attempting to achieve intrauterine growth rates based on maintaining a growth trajectory that follows the percentile found at birth (requiring a weight gain velocity of 15–17 g/kg/d depending on the growth curve) may not be appropriate because of obligatory weight loss due to fluid shifts during the first week of life . The authors suggested that a growth trajectory that has a goal of maintaining weight at discharge of ≥−0.8 z scores from the birth percentile may be more appropriate.…”

Postdischarge growth assessment in very low birth weight infants

“…Recently, there are other opinions about the adjustment of postnatal growth trajectories because all neonates including very preterm infants lose extracellular fluid after birth and tend to follow a lower percentile than their birth percentile16). However, extrauterine growth restriction commonly occurs in neonatal units1718).…”

Improved growth of extremely and very preterm babies: Evaluation of a quality‐of‐care initiative

“…It should be noted that using weight conflates changes in the extracellular fluid compartment and subsequent nutrition . In an ‘ideal’ preterm population, weight z score change of −0.8 within the first 2 weeks of life was demonstrated due to the contraction of the extracellular space and was maintained at least until day 21 – therefore, the post‐intervention z score change of −0.76 at 28 days may represent appropriate nutrition. However, by discharge, current recommendations are that birth z score should be regained …”