Li, Yan
Fu, Xiaoyu
Guo, Xinmeng
Liang, Huili
Cao, Dongru
Shi, Junmei
Article History
Received: 22 March 2022
Accepted: 25 August 2022
First Online: 14 September 2022
Declarations
:
: All procedures performed in this study in accordance with the Declaration of Helsinki. This study was granted exemption ethics approval by the Ethics Committee of Beijing Haidian Maternal and Child Healthcare Hospital due to the data used in this study from the open access NVSS database, and the relevant information of participants was anonymized and did not involve human intervention.
: Not applicable.
: The authors declare that they have no competing interests.