Premature Infant Growth – How Fast is Fast Enough? :

In a recently released article in Pediatrics(10.1542/peds.2017-2467), Dr. José Villar and a team of colleagues introduce the new INTERGROWTH-21st Preterm Postnatal Growth Standards, intended for growth monitoring of moderately preterm infants from birth through 64 weeks postmenstrual age (“corrected age” 6 months). Almost 1 in 10 babies are born prematurely, and accurate growth monitoring is clearly critical due to this population’s higher risk for poorer outcomes¹. In work funded by the Bill and Melinda Gates Foundation, the authors created international growth standards for preterm infants >27 weeks gestation that are based on longitudinal data from healthy low risk breastfed premature infants, analogous to the WHO (World Health Organization) Child Growth Standards for term infants, which are similar but utilize term infants’ growth. These new standards challenge the older supposition that the growth of preterm infants should match that of fetuses. Paradoxically, by this widely accepted “fetal” definition of adequate growth, about half of apparently well cared for premature infants leave the NICU (neonatal intensive care unit) with a label of “severe growth failure.” The remarkable convergence at term (40 weeks) of the INTERGROWTH-21st Preterm Postnatal Growth Standards and the WHO Child Growth Standards at the same mean weights (3.3 kg), lengths and head circumferences is indeed impressive and supports the authors’ arguments for the validity of this new approach.  

The authors make many good points in their discussion of the limitations and strengths of this new approach, and anyone who provides care for current premature babies (neonatologists) or for former premature babies (which is all practicing pediatricians!) will find the conversation highly relevant to NICU and office practice. If fetal growth is the goal, the authors suggest that premature infants are being “stuffed” with calories to avoid the all-too-frequent NICU-graduate label of “growth restriction,” yet their body composition at 40 weeks or term has proportionately more fat than fat-free mass compared to newborns born at term².  The “needed” calories may be going into a metaphorical “tire around the waist,” and the implications for the current obesity epidemic are obvious! You may agree or disagree with this thinking, but the authors’ argument is well constructed and worth reading.

Those whose reading includes other pediatric journals may want to compare this interesting article with the just published study of Dr. TR Fenton and esteemed colleagues³, whose works have anchored the approach to growth of premature infants for several decades. Dr. José Villar discusses the pragmatic and theoretical differences between the growth chart standards recently revised by Dr. Fenton and colleagues with the new INTERGROWTH-21st Preterm Postnatal Growth Standards.  I suspect that there would be a lively and thoughtful debate if we could get the authors of these two publications in the same room at the same time! In the meantime, enjoy the intriguing and useful contribution of Dr. José Villar and colleagues, which gives us a well-evidenced method of monitoring the growth of the premature infants for whom we provide care.

References

1. Preterm Birth. Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion. Centers for Disease Control and Prevention. Page last updated November 27, 2017. <https://www.cdc.gov/reproductivehealth/maternalinfanthealth/pretermbirth.htm> (accessed 1/3/2018)
2. Johnson MJ, Wootton SA, Leaf AA, Jackson AA. Preterm birth and body composition at term equivalent age: a systematic review and meta-analysis.Pediatrics. 2012;130(3):e640-649.
3. Fenton TR, Anderson D, Groh-Wargo S, Hoyos A, Ehrenkranz RA, Senterre T  An Attempt to Standardize the Calculation of Growth Velocity of Preterm Infants-Evaluation of Practical Bedside Methods. J Pediatr. 2017 Dec 12. pii: S0022-3476(17)31346-X. doi: 10.1016/j.jpeds.2017.10.005.