Funding for this research was provided by:
Ministry of Science and Technology of the People's Republic of China (2016YFC1000501)
Received: 24 July 2020
Accepted: 24 May 2021
First Online: 5 June 2021
: This study was approved by the biomedical ethics committee of Peking University (Beijing, China), and all mothers provided consent before participation.
: Not applicable.
: The authors declare that they have no competing interests.