Lu, Boqi
Zhang, Liping
Article History
Received: 22 February 2023
Accepted: 17 October 2023
First Online: 27 October 2023
Declarations
:
: The study was performed in accordance with the Declaration of Helsinki, and approved by the National Center for Health Statistics (NCHS) Ethics Review Board (ERB) (Continuation of Protocol #2005-06; continuation of Protocol #2005-06; continuation of Protocol #2011-17; Protocol Code #2018-01, effective beginning October 26, 2017; continuation of Protocol Code #2011-17, effective through 26 October 2017). Thus, the requirement of ethical approval for this was waived by the Institutional Review Board of Huai’an maternal and child health care center. Written informed consent was not required as this study was based on publicly available data. All methods were performed in accordance with the relevant guidelines and regulations.
: Not applicable.
: The authors declare no competing interests.