Racial and ethnic disparities in postnatal growth among very low birth weight infants in California

Postnatal growth is a critical concern for preterm infants, impacting brain development and long-term health. While survival rates have improved, racial and ethnic disparities in postnatal growth remain poorly understood. Previous research has shown varied definitions and measurements of postnatal growth failure (PGF) in preterm infants, with some studies indicating a decline in PGF over time due to improved nutritional support and care practices. However, disparities in fetal growth, infant postnatal growth rates, and nutrition practices (such as breastfeeding) persist across racial and ethnic groups. Studies have shown varying associations between maternal race/ethnicity and infant growth outcomes, with some reporting higher risks of small for gestational age (SGA) among infants of Black or Asian mothers and others highlighting differences in weight gain velocity and body composition across races. The current study aimed to investigate racial/ethnic differences in PGF among VLBW infants in California, focusing on longitudinal trends and associated factors.

Existing literature demonstrates inconsistent findings regarding racial/ethnic disparities in postnatal growth among preterm infants. Studies using different methodologies and definitions of PGF have reported varying prevalence rates and risk factors. Some research highlights the improved growth outcomes observed in quality improvement collaboratives focused on enhanced nutritional support. However, significant gaps remain in our understanding of the specific growth trajectories and disparities across different racial and ethnic groups, necessitating further research to guide targeted interventions.

This retrospective cohort study utilized data from the California Perinatal Quality Care Collaborative (CPQCC) database (2008-2016), encompassing 37,122 VLBW infants (birth weight 500-1500 g or gestational age 23-34 weeks). PGF was defined as a change in weight Z-score from birth to discharge below -1.28, using the Fenton growth charts. A subgroup analysis was performed on 20,019 infants with birth weight below 1000 g or gestational age 23-28 weeks. Multivariable logistic regression analysis, with birth hospital as a random effect, was used to identify factors associated with PGF, including race/ethnicity, sex, gestational age, maternal characteristics (age, education, insurance), and neonatal morbidities (SGA, maternal hypertension, chorioamnionitis, CLD, necrotizing enterocolitis, late-onset sepsis). Data on feeding type (formula only or human milk only) at discharge were also included. Statistical analyses were performed using SAS version 9.4, with p-values <0.05 considered statistically significant.

Among the 37,122 infants, maternal race/ethnicity distribution was 47% Hispanic, 26% White, 13% Black, and 11% Asian/PI. Hispanic infants had the highest incidence of PGF (30%), significantly higher than White (24%), Black (22%), and Asian/PI (23%) infants (ORs ranged from 1.33 to 1.50). PGF incidence decreased significantly from 2008 to 2016 (27% to 23%). Each additional week of gestational age was associated with a decreased risk of PGF (OR 0.73). In multivariable analysis, Hispanic ethnicity was independently associated with an increased risk of PGF, while Black race was associated with a decreased risk. Other significant factors associated with PGF included sex, formula feeding only, maternal hypertension, and SGA at birth. Subgroup analysis of infants with birth weight <1000g or gestational age 23-28 weeks showed similar patterns, although the incidence of PGF was lower among Hispanic infants in this subgroup compared to the full cohort. Figures 1, 2, and 3 in the original paper illustrate the incidence of SGA and PGF across different racial/ethnic groups, gestational ages, and time periods.

This large, population-based study confirms the existence of racial and ethnic disparities in postnatal growth among VLBW infants. The finding that Hispanic infants had the highest PGF risk, despite having lower SGA rates at birth, suggests that factors beyond birth weight contribute to postnatal growth failure in this group. The study highlights the importance of targeted interventions focused on improving nutritional support and addressing other contributing factors, such as comorbidities and potentially underlying socio-economic factors. The overall decline in PGF incidence from 2008 to 2016 suggests the effectiveness of population-level interventions aimed at improving neonatal care. However, the persistent disparities across racial and ethnic groups underscore the need for culturally sensitive interventions tailored to the specific needs of each population.

This study reveals significant racial and ethnic disparities in postnatal growth among VLBW infants in California, with Hispanic infants experiencing the highest risk of PGF. Early interventions focusing on nutrition optimization and addressing associated morbidities are crucial to mitigate these disparities and improve short- and long-term outcomes. Future research should investigate underlying social determinants of health and explore culturally sensitive interventions to address the observed disparities.

Several limitations exist: The study lacked quantitative nutritional data and only assessed growth at birth and discharge, potentially overlooking important variations in growth trajectories. Feeding data were collected at discharge only. Maternal smoking, obesity, and BMI were not considered. Exclusion criteria (death before discharge, discharge after 51 weeks PMA) may have introduced survivor and selection bias. The association should not be interpreted as causal due to potential confounding from unobserved variables.