The Lubchenco curves may not represent the current US population. The new intrauterine growth curves created and validated in this study, based on a contemporary, large, racially diverse US sample, provide clinicians with an updated tool for growth assessment in US NICUs. Research into the ability of the new definitions of small-for-gestational-age and large-for-gestational-age to identify high-risk infants in terms of short-term and long-term health outcomes is needed.

Variation in nutrition explained much of the difference in growth among the NICUs studied. Mean intake of calories and protein failed to meet recommended levels, and the average growth in only 1 NICU approximated intrauterine growth standards. Increasing nutritional intake into the recommended ranges, in particular of protein, may increase growth of extremely premature infants up to or above intrauterine rates.

BACKGROUND AND OBJECTIVES: Preterm infants experience disproportionate growth failure postnatally and may be large weight for length despite being small weight for age by hospital discharge. The objective of this study was to create and validate intrauterine weight-for-length growth curves using the contemporary, large, racially diverse US birth parameters sample used to create the Olsen weight-, length-, and head-circumference-for-age curves.METHODS: Data from 391 681 US infants (Pediatrix Medical Group) born at 22 to 42 weeks' gestational age (born in 1998-2006) included birth weight, length, and head circumference, estimated gestational age, and gender. Separate subsamples were used to create and validate curves. Established methods were used to determine the weight-for-length ratio that was most highly correlated with weight and uncorrelated with length. Final smoothed percentile curves (3rd to 97th) were created by the Lambda Mu Sigma (LMS) method. The validation sample was used to confirm results. RESULTS:The final sample included 254 454 singleton infants (57.2% male) who survived to discharge. BMI was the best overall weight-for-length ratio for both genders and a majority of gestational ages. Gender-specific BMI-for-age curves were created (n = 127 446) and successfully validated (n = 126 988). Mean z scores for the validation sample were ∼0 (∼1 SD).CONCLUSIONS: BMI was different across gender and gestational age. We provide a set of validated reference curves (gender-specific) to track changes in BMI for prematurely born infants cared for in the NICU for use with weight-, length-, and head-circumference-for-age intrauterine growth curves. WHAT'S KNOWN ON THIS SUBJECT:Preterm infants experience disproportionate growth failure postnatally and may be large weight for length despite being small weight for age by hospital discharge. There is no routinely used measure to quantify and monitor disproportionate growth in the NICU.WHAT THIS STUDY ADDS: BMI differs across gender and gestational age. We provide a set of validated reference curves to track changes in BMI for prematurely born infants for use with weight-, length-, and head-circumference-for-age intrauterine growth curves.

Higher cumulative protein intake was tolerated and overall lessened the commonly occurring decline in the length but not weight growth status in a 28-day study of preterm infants.

Objective-We evaluated the utility of weight-for-length (defined as gm/cm 3 , "ponderal index") as a complementary measure of growth in infants in neonatal intensive care units (NICUs).Study design-Secondary analysis of infants (n=1214) 26-29 weeks at birth, included in a registry database (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003), who had growth data at birth and discharge. Weight-for-age and weight-forlength were categorized as small (<10 th percentile), appropriate or large (>90 th percentile).Results-Statistical agreement between the weight-for-age and weight-for-length measures was poor (kappa=0.02 at birth, 0.10 at discharge, Bowker test for symmetry p<0.0001). From birth to discharge, the percent of small-for-age infants increased from 12% to 21%, and the percent of smallfor-length infants decreased from 10% to 4%; the percent of large-for-age infants remained similar (<1%), and the percent of large-for-length infants increased from 5% to 17%. At discharge, 92% of small-for-age infants were appropriate or large-for-length, and 19% of appropriate-for-age infants were large-for-length.Conclusions-Weight-for-age and weight-for-length are complementary measures. Weight-forlength or other measure of body proportionality should be considered for inclusion in routine growth monitoring of infants in the NICU.Corresponding Author: Irene E. Olsen PhD, RD, LDN, Drexel University, Department of Bioscience and Biotechnology, 3141 Chestnut Street, Philadelphia, PA 19104, Phone: 215-895-5834, FAX: 215-895-1273, E-mail: irene.olsen@drexel .edu. Edtied by Padbury and ShermanPublisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access KeywordsGrowth status; growth; weight-for-age; weight/length 3 ; ponderal index; weight/length ratio; obesity; overweight; underweight; small-for-gestational age; nutrition A body proportionality index provides an assessment of body mass relative to length or height. Body mass index (BMI = weight/height 2 ) in children and adults is known to be highly correlated with body fatness and risk of related diseases (1). Thus, BMI has become an important part of health assessment.Prematurity is the only period during the lifecycle for which a body proportionality index, such as BMI, is not routinely used to assess body size. Even though comparing an infant's weight to fetuses of the same gestational age, or weight-for-age (2-7) is an excellent measure of overall size, it cannot detect situations where weight growth exceeds or fails to keep up with growth in the infant's length. This is potentially a problem f...

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Background: Clinicians have observed preterm infants in the neonatal intensive care unit growing disproportionally; however, the only growth charts that have been available were from preterm infants born in the 1950s which utilized the ponderal index. Prior to creating the recently published BMI curves, we found only 1 reference justifying the use of the ponderal index. Objectives: To determine the best measure of body proportionality for assessing growth in US preterm infants. Methods: Using a dataset of 391,681 infants, we determined the body proportionality measure that was most correlated with weight and least correlated with length. We examined the sex-specific overall correlations and then stratified further by gestational age (GA). We then plotted the body proportionality measures versus length to visualize apparent discrepancies in the appropriate measure. Results: The overall correlations showed weight/length³ (ponderal index) was the best measure but stratification by GA indicated that BMI (weight/length²) was the best measure. This seeming inconsistency was due to negative correlations between ponderal index and length at each GA. BMI, on the other hand, had a correlation with length across GAs, but was uncorrelated with length within GAs. Both ponderal index and BMI were positively correlated with weight. Conclusions: BMI is the appropriate measure of body proportionality for preterm infants, contrary to current practice.

Children with AGS have deficits in bone size and bone mass relative to body size. Modifiable factors, such as treatment of malabsorption should be explored as an early focus of AGS care to prevent bone fragility.