Greenness, nighttime light, and couple fecundability: A national cohort study between 2014 and 2020

Reduced greenness and increased nighttime light (NTL) have been associated with adverse health outcomes; however, the impacts of greenness and NTL on human fecundability remain uncertain.

Data was collected from 14,239,365 couples across 31 provinces in China. Greenness exposure was estimated using the Normalized Difference Vegetation Index (NDVI) within 1000-m buffer zones, while NTL data was derived from the Visible and Infrared Imaging Suite Day Night Band aboard satellites, both based on individual residential addresses. Fecundability among the couple participants was measured as time to pregnancy in cycles. The associations between fecundability and annual greenness or NTL exposure were assessed using variable-adjusted accelerated failure time models. Further, subgroup analyses were performed based on couples' age, body mass index, educational levels, registration regions, and other environmental factors.

Each interquartile range (IQR) increase in annual NDVI levels was significantly associated with shorter TTP (time ratio: 0.9881; 95% confidence interval [95% CI]: 0.9862, 0.9901), while per IQR increase in annual NTL level was significantly associated with longer TTP (time ratio: 1.0340; 95%CI: 1.0326, 1.0354). The associations were more pronounced among participants who were older, overweight, had lower educational levels, resided in urban regions, or lived in areas with poorer environmental conditions.

This cohort study has revealed that decreased greenness and increased NTL exposure were associated with reduced couple fecundability, highlighting the importance of developing greener and healthier cities in prompting global reproductive health.