Funding for this research was provided by:
the Research Funds of Profession Quota Budget from Beijing Municipal Science and Technology Commission (2020-bjsekyjs)
Received: 18 August 2020
Accepted: 22 December 2020
First Online: 7 January 2021
Ethics approval and consent to participate
: The Institutional Review Board and Committee on Human Research at Beijing Children’s Hospital approved the study (No. 2016–3). The mothers gave written consent for their participation and their children’s participation.
: Not applicable.
: The authors declare that they have no competing interests.