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Pediatrics. 2015 Mar;135(3):e572-81. doi: 10.1542/peds.2014-2777. Epub 2015 Feb 16.

BMI curves for preterm infants.

Author information

School of Nursing, University of Pennsylvania, Biology and Physics, and
Statistics and Analytical Sciences, College of Science and Mathematics, Kennesaw State University, Kennesaw, Georgia; and
Statistics and Analytical Sciences, College of Science and Mathematics, Kennesaw State University, Kennesaw, Georgia; and.
Division of Gastroenterology, Hepatology and Nutrition, The Children's Hospital of Philadelphia, and Department of Pediatrics, The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; Departments of.
Pediatrix Medical Group, Inc, Sunrise, Florida.



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.


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.


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).


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.


BMI; body proportionality; growth; growth curves; intrauterine growth curves; large for gestational age; length for age; nutrition; relative weight; small for gestational age; weight for age

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