Study settings and subjects
We selected all hospitals in Foshan (n=62) and several other hospitals in Guangzhou (n=1), Shenzhen (n=1), Dongguan (n=2), and Jiangmen (n=1) in Guangdong Province, South China, as study settings (Figure 1 - Map). All hospital birth data from 1/1/2015 to 12/31/2020 were collected (n=749059). Birth records with multiple births (n=27659), stillbirths (n=726), or missing information on key variables (n=2883) were excluded. Moreover, 122395 births were excluded because their pregnancy did not overlap with the COVID-19 lockdown in 2020 or the same calendar months in 2015-2019. Finally, 595396 mother-newborn pairs were included. None of these women had a positive SARS-CoV-2 test result (Figure S1 - Flowchart).