Environmental exposure to outdoor artificial light at night during pregnancy and fetal size: A prospective cohort study

Previous studies suggested outdoor artificial light at night (ALAN) exposure may contribute to children and adult obesity, but less is known about the associations of outdoor ALAN exposure during pregnancy with fetal size. From 2015 to 2021, 6210 mother-child pairs were included. Average outdoor ALAN levels during pregnancy were measured using satellite imaging data. Fetal biparietal diameter, head circumference, abdominal circumference (AC), and femur length were measured before delivery with ultrasonography . We also collected anthropometric birth outcomes, including birth length, birth weight, macrosomia , low birth weight, small for gestational age , and large for gestational age at delivery. Multivariable linear regression models and binary logistic regression models were used to examine the potential associations of outdoor ALAN with fetal size adjusting for a broad set of potential confounds. An IQR (14.87 nW/cm 2 /sr) increase in outdoor ALAN during pregnancy was associated with 1.30 (β = 1.30, 95 % CI: 0.31,2.29) higher AC percentiles and 13 % (OR = 1.13, 95 % CI: 1.00,1.27) higher odds of macrosomia after adjusting confounders. In sex stratification analysis, an IQR (14.87 nW/cm 2 /sr) increase in outdoor ALAN during pregnancy was associated with 1.65 (β = 1.65, 95 % CI: 0.24,3.06) higher fetal AC percentiles and 27 % (OR = 1.27, 95 % CI: 1.06,1.53) higher odds of macrosomia in females. Our findings suggest that higher outdoor ALAN exposure during pregnancy is associated with larger fetal AC and a higher risk of macrosomia, particularly in the female fetus. Future studies are needed to verify these preliminary findings and identify potential mechanisms for the association. • Maternal expose to outdoor ALAN was associated with larger fetal AC. • Maternal expose to outdoor ALAN was associated with a higher risk of macrosomia. • The association between outdoor ALAN and fetal size was stronger in females. • The second trimester is the susceptibility window of ALAN exposure on fetal size.