Received: 3 April 2019
Accepted: 17 December 2019
First Online: 31 December 2019
Ethics approval and consent to participate
: Both ethics approval and permission to conduct this study was obtained from the ethics boards of the Hong Kong Polytechnic University (Reference No. HSEARS20181015003) and the Shenzhen Maternity and Child Healthcare Hospital (Reference No. 2018278). Written informed consent to take part in the study was obtained from the participants during the process of recruitment.
: Not applicable.
: The authors declare that they have no competing interests.