Received: 6 January 2022
Accepted: 26 May 2022
First Online: 8 June 2022
: The study was approved by the Ethics Committee of the Obstetrics and Gynecology Hospital of Fudan University (No. 2017–35, 2017–35-C1) and was conducted following Chinese law and the Guidelines of the National Human Biomedical Research Policy. No informed consent was obtained from the patients because the study was retrospective. The informed consent was waived by the Ethics Committee of the Obstetrics and Gynecology Hospital of Fudan University. Administrative permissions for the data were acquired by the authors for research purposes.
: Not applicable.
: The authors declare that they have no competing interests.