3.3.1 Abortion rate before 28 weeks
Five studies were included for this analysis[9-11, 14, 15]. Due to statistical homogeneity across studies (P =0.97, I 2=0%), a fixed-effect model was applied. Results showed that the abortion rate before 28 weeks was comparable between the cervical pessary group and the cervical cerclage group (RR =0.57, 95%CI : 0.29 to 1.09, P =0.97) (Figure 1-2).