Funding for this research was provided by:
Science and Technology Planning Project of Shenzhen Municipality (JCYJ20170306155909623)
Received: 28 February 2020
Accepted: 23 July 2020
First Online: 31 July 2020
Ethics approval and consent to participate
: This study had the approved by the Ethics Committee of the Shenzhen Nanshan Maternal and Child Health Care Hospital. All parents of the children participated provided written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.