Patients selection
This study was approved by the ethical committee of Beijing Obstetrics and Gynecology Hospitaland was registered at clinical trials registry on 13/09/2017 with registration ID: ChiCTR-INR-17012659.The informed consent was signed by every parturient after explanation of aim, risks and benefits of the study.A total of 160 parturient, aged 22–35 years old, body weight between 55 to 85 kg, who delivered in Beijing Obstetrics and Gynecology Hospital from September 2017 to September 2020 were enrolled. They were randomly divided into CSA group and EA group with 80 cases in each group. The sample size was calculated using PASS 15.0 software, and a two-sided test with a test level of 0.05 and a test efficacy of β = 0.2 was used, and the rate of loss was calculated at 10%.