Objective To evaluate the effect of mifepristone in the treatment of low-risk cesarean scar pregnancy（CSP）by three-dimensional ultrasound.MethodsTwenty-nine patients with CSP whose systemic score was less than 5（CSPgroup）

and 25 patients with scar intrauterine pregnancy（IUP group）were included.Three-dimensional ultrasound was used tomonitor changes in vascular index（VI）

blood flow index（FI）

and vascular blood flow index（VFI）

as well as VI difference

FIdifference

and VFI difference around the gestational sac before and after oral administration of mifepristone[ie VI difference=VI（front）-VI（rear）

FI difference=FI（front）-FI（rear）

VFI difference=VFI（front）-VFI（rear）].ResultsThe VI and VFIaround the gestational sac of the CSP group and the IUP group after taking mifepristone for 2 d were significantly lower thanbefore administration

and the differences were statistically significant（both P<0.05）.VI

FI

VFI of CSP group and IUP groupwere（3.34%±2.64%）vs.（2.37%±2.29%）

（1.45±4.31）vs.（0.92±4.94）

（1.80±1.46）vs.（1.25±1.28）

respectively.Therewere no significant difference of these indicators between the two groups before and after treatment with mifepristone.And therewas no significant difference in the total effective rate between the two groups.ConclusionThree-dimensional ultrasound isused to monitor the effect of mifepristone in CSP patients with ultrasound quantitativ score less than 5. It is considered thatroutine drug abortion combined with uterine curettage is effective for CSP patients.