Ethics approval and consent to participate
The study was approved by the Ethics committee of Peking University First Hospital (Reference Number: 2020–247, on 30/10/2020) and registered prior to patient enrollment at Chinese Clinical Trial Registry (ChiCTR2000040343, on 28/11/2020). Written informed consent was obtained from each recruited parturient after providing them with adequate explanations regarding the aims of this study. The principles of Declaration of Helsinki were followed for this study.