Received: 30 June 2020
Accepted: 5 October 2020
First Online: 9 October 2020
Ethics approval and consent to participate
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the Hospital Human Subjects Ethics Committee, Shengjing Hospital of China Medical University. The study was approved by the Hospital Human Subjects Ethics Committee and any consent to participate was obtained from those who were contacted via telephone. Consent obtained from all participants was verbal and the ethics committee approved this procedure, because this study was a retrospective study based on database, it will not affect the routine procedures of the examination, nor will it cause any harm to pregnant women and fetuses. This article does not contain any studies with animals performed by any of the authors.
: Not Applicable.
: The authors declare that they have no competing interests.