The Natural History of Weight Percentile Changes in the First Year of Life

The Centers for Disease Control and Prevention ¹ and the World Health Organization² have published growth curves derived from the z scores of cross-sectional data in children^3,4 who have become an integral part of pediatrics. Children whose growth curves fall below these curves are said to have failure to thrive. Growth curves may be useful to determine whether a patient’s values are within a normal range, but they do not capture the longitudinal perspective essential for determination of health. We followed up patients longitudinally using a large outpatient electronic medical record to determine changes in weight percentile during their first year of life.

Data were obtained from an existing electronic medical record used in 4 pediatric clinics including the Child Health Improvement through Computer Automation system, which uses the Centers for Disease Control and Prevention weight-for-age growth curve.^1,2 Institutional review board approval was obtained at Indiana University and consent for participation was waived owing to the retrospective nature of the study. We performed 3 measurements in our sample: (1) the number of percentile lines (defined as the fifth, 10th, 25th, 50th, 75th, 90th, or 95th percentiles) crossed before 1 year, (2) the rate of change of weight before 1 year, and (3) the difference between the first and last measurement. To assess the effect of demographic variables, we built a linear regression model using R (R Project for Statistical Computing).

Children’s characteristics are shown in the Table. Sixty-four percent of children’s weight curves decreased by at least 1 line, 38% fell by at least 2 lines, and 35% increased or did not change. Thirty-one percent decreased 2 lines over a 6-month period and thus could be defined as failure to thrive. Thirty-three percent of black patients (P < .001), 43% of Hispanic patients (P < .001), and 34% of white patients fell at least twice. Sixty-six percent of boys and 51% of girls decreased by at least 1 line and 41% of boys and 34% of girls decreased by at least 2 lines.

These results are displayed in the Figure. Of all the children, 44%, 29%, and 27% had negative, positive, and no rate of change in percentiles, respectively. Ten percent of children’s curves decreased by 4 lines per year or more, 20% decreased by 3 lines per year or more, and 40% decreased by 1 line per year or more. Forty-eight percent of black children (P = .38), 41% of Hispanic children (P < .001), and 44% of white children had a negative rate of change. Forty-one percent of boys and 47% of girls had a negative rate of change (P < .001).

Twenty-seven percent of patients had no change, 62% were within 1 line of where they started, 44% of patients decreased by 1 line or more, and 29% increased by 1 line or more. Twenty-five percent of patients decreased by at least 2 lines and 13% of patients increased by at least 2 lines.

We assessed the trends in weight percentile change that occur in children during the first year of life. We found that more than 64% of children decreased by 1 percentile line or more at some point in this period and 44% of children were at a lower percentile than where they started. Our results suggest that many children’s growth percentiles decline during the first year of life, and this may be normal. Limitations to this study included retrospective assessment of growth, limiting to children younger than 1 year of age, a population of mostly minority patients on Medicaid, and lack of assessment of other socioeconomic variables (eg, maternal education and household income). Our results may differ slightly when UK growth records are used (when analysis was repeated using UK centiles, 4.9% of visits were different when compared with US centiles). Intense study of the longitudinal nature of normal growth may help us better recognize cases of failure to thrive and limit unnecessary use of resources for what, in many cases, may be a normal phenomenon.

Corresponding Author: William E. Bennett Jr, MD, Section of Pediatric Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Indiana University School of Medicine, 410 W 10th St, Indianapolis, IN 46202 (webjr@iupui.edu).

Published Online: May 5, 2014. doi:10.1001/jamapediatrics.2014.345.

Author Contributions: Dr Bennett had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: All authors.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Bennett.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Bennett, Thompson, Carroll, Downs.

Obtained funding: Downs.

Administrative, technical, or material support: Downs.

Study supervision: Downs.

Conflict of Interest Disclosures: None reported.