A 29-year-old woman was diagnosed with a cervico-isthmic pregnancy based on ultrasound findings at 8 weeks of gestation. At 30 weeks of gestation, placenta previa was confirmed. During cesarean section at 37 weeks, the placenta did not spontaneously detach from the uterus; therefore, we decided to leave it in the uterus to avoid major hemorrhage. Blood loss was 775 mL and a healthy infant was delivered. After the operation, weekly methotrexate injection was initiated. Shortly after the eighth course of injection, massive vaginal bleeding suddenly occurred and bilateral uterine artery embolization was performed to control it. After the procedure, the retained placental tissue was removed and the patient was discharged with good general condition. Although a cervico-isthmic pregnancy constitutes a high-risk pregnancy, fertility-sparing management without a hysterectomy or blood transfusion was possible by not removing the placenta manually during the operation.