Prenatal exposure to outdoor artificial light at night and neonatal thyroid function: Identifying critical windows of...

Outdoor artificial light at night (ALAN) is an emerging environmental pollutant of global concern. Although prenatal ALAN exposure has been linked to adverse pregnancy outcomes, its association with neonatal thyroid function, critical for early growth and neurodevelopment, remains unexplored. We examined the relationship of maternal outdoor ALAN exposure with neonatal thyroid-stimulating hormone (TSH) levels.

We conducted a retrospective cohort study involving 77,472 mother-newborn pairs in Guangzhou, China (2016-2022), estimating maternal ALAN exposure by integrating satellite-derived data with residential addresses and quantifying neonatal TSH levels from heel-stick blood samples. Multiple linear regression models were employed to evaluate the relationship between ALAN exposure and neonatal TSH.

Generally inverse dose-response relationships were observed between prenatal ALAN exposure and neonatal TSH levels. Compared with the lowest exposure quartile, the highest quartile of ALAN exposure was associated with a 3.43% decrease in neonatal TSH levels (95% CI: -5.11%, -1.73%) during the first trimester, a 2.52% decrease (95% CI: -4.20%, -0.82%) during the second trimester, and a 2.63% decrease (95% CI: -4.31%, -0.92%) across the entire pregnancy. The associations between prenatal ALAN exposure and neonatal TSH levels were more evident among multiparous women.

These findings suggest that prenatal ALAN exposure, particularly in early-to-mid pregnancy, is associated with reduced neonatal TSH levels, suggesting that early-to-mid pregnancy may represent a susceptible window and that environmental light pollution may influence early-life endocrine function.