Childhood growth is a sensitive indicator of health and development, shaped by both biological and environmental factors. Early-life exposures, such as neonatal antibiotic treatment and socioeconomic disadvantage, may influence growth trajectories through complex mechanisms. The gut microbiota, which develops rapidly during infancy, has been proposed as a key mediator linking early exposures to long-term outcomes such as overweight and obesity.

This study examined the associations between neonatal antibiotic exposure, neighborhood socioeconomic status, and childhood growth, and explored the mediating role of the gut microbiota. These associations were studied in the population-based Southwest Finland Birth Cohort, consisting of 14946 children. Growth data were collected from municipal well-baby clinics, and antibiotic exposure was assessed from hospital and prescription records. Neighborhood socioeconomic disadvantage was derived for national grid-based statistics. The impact of perinatal antibiotic exposure on gut microbiota composition was investigated in a well-defined group of infants using 16S rRNA sequencing, and finally fecal microbiota transplantation (FMT) was performed in germ-free mice to explore causality.

We found that neonatal antibiotic exposure was associated with reduced weight and height gain during the first six years of life in boys, while later antibiotic use correlated with increased BMI in both sexes. Socioeconomic disadvantage predicted higher BMI trajectories from age four. Gut microbiota analyses revealed persistent alterations, particularly reduced Bifidobacterium abundance, following neonatal antibiotic exposure. FMT from antibiotic-exposed infants led to impaired growth in male mice, supporting a causal role for microbiota alterations.

These findings suggest that neonatal antibiotic exposure and living in a neighborhood with socioeconomic disadvantage are linked to altered growth patterns in childhood. The gut microbiota is a potential causal mediator of growth disturbances, highlighting its role in early-life health programming. Prudent antibiotic use and addressing social determinants of health may provide avenues for improving child health.