Article History
Received: 10 December 2020
Accepted: 29 September 2021
First Online: 12 October 2021
Declarations
:
: This clinical study is a retrospective study. For this kind of research, the Principles of the Declaration of Helsinki should be complied with, and the study is approved by the ethics committee of Haidian Maternal and Child Health Hospital on May 10, 2021.
: Not applicable.
: The authors declare that they have no competing interests.