Trajectories of Outdoor Light at Night, Small for Gestational Age, and Effect Modification by Socio-Economic Status: A Population-Based Retrospective Cohort Study

Outdoor artificial light at night (ALAN) is a widespread environmental pollution associated with the urbanization worldwide. Whether its trajectories as well as temporal patterns increase the risk of small for gestational age (SGA) remains underexplored. Based on a national population-based retrospective cohort study including 572,989 women of reproductive age (21-49 years) across 220 counties in China and satellite ALAN data, this study aimed to explore the association between the trajectories of ALAN and SGA and the effect modification by socio-economic status (SES). Group-based trajectory models according to the lowest Bayesian information criterion were used to characterize the trajectories of ALAN. Logistic regression models were used to estimate the risk ratios (RRs) of SGA associated with different trajectories of outdoor ALAN, as well as the effect modification by age, education, occupation, and region. We identified three latent classes, including low- [n = 304,577, 53.2%], moderate- [208,290, 36.4%], and high- [60,122, 10.5%] curve groups. Compared to the low-curve group, the high-curve group exhibited the highest risk of SGA (RR = 3.16, 95% CI: 2.76-3.63), followed by the moderate-curve group (RR = 1.25, 95% CI: 1.12-1.40) (P for difference <0.001). Similar associations were observed across all SES subgroups. These findings suggest that higher trajectories of outdoor ALAN exposure are associated with increased risks of SGA across populations with different SES levels.