Supplementary file 1_Maternal SO2 exposure and birthweight reduction during COVID-19 lockdown and quarantine in East China.docx

While maternal exposure to certain air pollutants is known to adversely affect fetal growth, the association with sulfur dioxide (SO₂) has been inconsistent. The COVID-19 lockdown provided a unique quasi-natural experiment to reassess the relationship under altered emission patterns.</p>Methods<p>We conducted a retrospective cohort study of 21, 777 term singleton births in Southern Zhejiang Province, East China, from 2020 to 2022.

We estimated maternal SO₂ exposure using a time-activity weighted model based on residential and work addresses. Associations with low and high birthweight risks were evaluated using linear regression and odds ratios. Three machine learning models were used to assess whether incorporating SO₂ exposure improved birthweight prediction accuracy.</p>Results<p>The COVID-19 lockdown was associated with a significant 28% reduction in annual mean atmospheric SO₂ levels.