BACKGROUND: Whether pre-pregnancy stress could modify the effects of outdoor artificial light at night (ALAN) on preterm birth (PB) has been unknown. This study aimed to explore the association between outdoor ALAN exposure and the risk of PB, as well as the effect modification by pre-pregnancy stress.
METHODS: This national population-based retrospective cohort study included women of reproductive age (21-49 years) from the National Free Preconception Health Examination Project (NPHCP) across 220 counties in China, from 2010 to 2012. ALAN exposure was quantified using satellite data, and pre-pregnancy stress was assessed via a structured questionnaire focusing on life, friend, economic, and total stress. The primary outcomes were PB (28-37 weeks) and extremely PB (<28 weeks). Logistic regression models were used to estimate the risk odd ratios (ORs) of PB along with per interquartile range (IQR) increase in ALAN exposure, as well as the potential effect modification by pre-pregnancy stress. Stratified analysis was also conducted to explore differences across socioeconomic status.
RESULTS: A total of 549,654 pregnant women were participated in this study. An IQR (8.0 nW/cm/sr) increase in 1-year average ALAN exposure was associated with ORs of 1.08 (95 %CI: 1.03-1.13) and 1.03 (95 %CI: 1.02-1.04) for extremely PB and PB, respectively. Higher pre-pregnancy life stress levels were associated with a stronger association between outdoor ALAN exposure (1-year average) and extremely PB, with an odds ratio of 1.04 (95 % CI: 0.97-1.10) in the lower group and 1.16 (95 % CI: 1.08-1.24) in the higher group (P for difference = 0.017). Higher total, life, economic, and friend pre-pregnancy stress may amplify the effect of ALAN on PB risk. For instance, an IQR increment in ALAN exposure was associated with ORs of 1.02 (95 % CI: 1.00, 1.03) and 1.07 (95 % CI: 1.05, 1.10) among participants with low and high total stress (P for difference <0.001). Stratified analyses indicated more apparent effect modifications by pre-pregnancy stress in participants with lower educational levels, with non-farmer occupation, living in rural areas, and living in south regions. 2
CONCLUSIONS: Our findings suggest that higher pre-pregnancy stress levels may amplify the risk of PB associated with outdoor ALAN exposure, especially among women with lower educational levels, of non-farmer occupation, and living in rural areas or in south regions.
