Rapid Weight Gain Among High-Risk Infants: Estimating Prevalence and Identifying Risk Factors Using Adverse Pregnancy Outcomes Reporting System Data in Cook County, Illinois *

BACKGROUND:   Rapid infant weight gain (RIWG) is an accelerated weight-for-age growth pattern in infants under two years of age. Research establishes a strong association between RIWG and subsequent obesity, cardiovascular disease, and diabetes. Various factors are associated with RIWG; however, existing studies focus on low-risk infants. This study’s purpose was to estimate the prevalence of RIWG among high-risk infants in suburban Cook County, Illinois, and identify potential RIWG risk factors.

METHODS:   Adverse Pregnancy Outcomes Reporting System records were accessed for a 4-month birth cohort (N=127) that received home visiting services through the Cook County Department of Public Health High Risk Infant Follow-up Program.  The dependent variable was whether an infant experienced RIWG between 3- and 6-month home visits, measured by calculating the difference between weight-for-age z-scores at each visit (adjusted for sex). An increase in z-score of ≥0.67 was considered RIWG. Independent variables included: sex, race/ethnicity, WIC enrollment, residential district, number/type of diagnoses, birth weight, gestational age, maternal age at birth, maternal education, and concurrent change in head circumference and height. Log binomial regression was used to create the most parsimonious model of RIWG. Final prevalence ratios were adjusted for other selected covariates and stratified by residential district (North, West, and South/Southwest).

RESULTS:   The overall prevalence of RIWG was 36.2% (n=46; 95%CI=27.9%, 44.6%). In the North district, every 5-year increase in maternal age at birth was associated with 1.6 times higher prevalence of RIWG (95%CI: 1.05, 2.3); this association was not found in other districts. In the North, infants with 2+ diagnoses had 1.2 times higher prevalence of RIWG compared to infants with one diagnosis (95%CI: 0.6, 2.4); in the South/Southwest, infants with 2+ diagnoses had 2.3 times higher prevalence of RIWG (95%CI: 0.9, 6.1); and in the West, infants with 2+ diagnoses had 0.6 times lower prevalence of RIWG (95%CI: 0.3, 1.4). 

CONCLUSIONS:  The RIWG prevalence estimate was higher than previous estimates (20-30%). Potential risk factors differed from those found in existing literature, suggesting that risk factors for high-risk infants may differ from those for low-risk infants. While certain results are not statistically significant due to sample size, findings suggest that risk factors differ by residential location, even when controlling for individual-level demographic and SES factors. Place-based factors should be considered in future analyses of RIWG within high-risk populations.