Received: 21 September 2019
Accepted: 25 March 2020
First Online: 2 April 2020
Ethics approval and consent to participate
: The ethics committee of Xiamen Maternal and Child Care Hospital of human body research approved the study (approval no. KY-2019-033). All procedures performed in studies involving human participants were in accordance with the ethics standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethics standards. The parents of all study participants provided written informed consent.
: All data published here received consent for publication.
: The authors declare that they have no competing interests.