Funding for this research was provided by:
Sanming Project of Medicine in Shenzhen (SZSM201803061)
Shenzhen Science and Technology Program (NO.JCYJ20150402100128583)
Received: 13 July 2019
Accepted: 25 February 2020
First Online: 6 March 2020
Ethics approval and consent to participate
: This study was approved by the ethics committee of the Maternal & Child Healthcare Hospital of Nanshan district in Shenzhen, and all participants provided written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.