Background The rate of cesarean scar pregnancy (CSP) is increasing in these years, and there is no consensus on therapy.

Objective To study the safety, efficacy and indications of ultrasound-guided local injection of methotrexate (MTX) in the treatment of CSP.

Methods CSP patients treated in the First Medical Center of Chinese PLA General Hospital from 2008 to 2022 were retrospectively recruited. The clinical information and imaging data of patients, as well as the success rate of ultrasound guided local injection of MTX treatment before and after treatment were compared. Then ROC analysis of β- HCG prediction efficiency was performed.

Results Of the included 107 CSP patients, 103 (96.26%) patients were treated successfully, among them 12 (11.65%) cases received additional MTX injection. The treatment failed in 4 (3.74%) patients with surgery intervention. β-HCG in the successful group was significantly lower than that in the failed group (MdIQR: 12 636.00 2 009.00 - 28 138.00 IU/L vs 36 678.00 33 076.25-147 204.30 IU/L, P=0.004). Patients received multiple injections of MTX had higher β-HCG than those received single injection (MdIQR: 9 157.00 1 390.80 - 24 888.60 vs 33 260.00 17 048.50 - 80 124.50, P=0.001). Only one patient had side effect and the liver transaminase elevated after therapy and improved several days later. ROC analysis showed that the AUC of treatment outcomes predicted by β-HCG was 0.927, and the AUC of the number of treatments (MTX injections) predicted by β-HCG was 0.792.

Conclusion Ultrasound-guided injection of MTX is a safe and effective modality to treat CSP. The change trends of β-HCG should be monitored, additional injection of MTX or surgery intervention could be performed to patients with lower β-HCG if necessary.