BMI Curves for Preterm Infants

Abstract

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.

Assessment of fetal malnutrition by body mass index and intra uterine growth curves: a comparative study

“…Body mass index (BMI) has been widely used for nutritional assessment and adiposity in children however underutilized in neonates. 5 This was partly due to lack of reference standards for different gestational ages. Olsen et al published reference BMI curves in 2015 and concluded that disproportionate growth failure in infants is best detected by gender specific BMI for age percentile curves when compared size for age methods.…”

“…Firstly, the body mass index was calculated using the formula: weight in kilograms/ length in metre 2 and plotted on the gender specific BMI charts by Olsen et al 5 BMI less than tenth percentile was considered as fetal undernutrition. Then, neonates were classified into appropriate for gestational age (AGA) if their birth weights ranged between 10 th and 90 th centiles for that gestational age, small for gestational age (SGA) if their weights fell below 10 th centile or large for gestational age (LGA) if their weights were more than 90 th centile on the various intra uterine growth charts.…”

“…The fetal malnourishment can get underestimated by these charts since a proportion of malnourished infants can still have normal weight for that gestational age. 5 The other methods are based on either individual anthropometric parameters like mid arm circumference, or their ratios, for example mid arm circumference to head circumference (MAC/HC) ratio. 6 Growth assessment is not complete when only one anthropometric parameter like weight is used since it does not identify growth that is disproportionate i.e.…”

“…5 These charts are gender specific and available for babies with gestational age between 22 and 42 weeks. This is the most recent chart based on weight to length ratio after those published by Lubchenco et al in 1966 andMiller andHassanein in 1971.…”

The Clinical and Policy Implications of New Measures of Premature Infant Growth

“…As pointed out in the recent article by Olsen et al, 1 the appropriate growth of a prematurely born infant may have a significant impact on his or her developmental and growth outcomes after discharge from the NICU. In fact, appropriate growth encompasses many aspects of the care of the premature infant besides the monitoring of growth parameters and providing appropriate fortified nutrition.…”