Cesarean section scar pregnancy (CSP) is a rare type of ectopic pregnancy where implantation occurs in the myometrium at a previous cesarean incision site [1]. However, CSP differs from typical ectopic pregnancies because the embryo invades and proliferates within the myometrium and fibrotic scar tissue [2]. The global rise in cesarean deliveries from approximately 6.7 % in 1990 to over 21 % in 2021, with projections indicating a further increase to nearly 29 % by 2030, has contributed to a growing incidence of abnormal implantations, including CSP [3]. CSP has been reported in 0.04 % to 0.05 % of all pregnancies in women with a history of cesarean delivery, and among those who have experienced CSP, the recurrence rate has been as high as 17.6 % [4].

Uterine rupture, which occurs with either dehiscence of the scar at the cesarean scar site or abnormally implanted fetal tissue into the myometrium, is a serious, and at times fatal, pregnancy complication that can cause maternal hemorrhage, hypovolemic shock, or even death [5]. Another complication is severe bleeding caused by the invasion and infiltration of trophoblast cells into vascular structures within the scar tissue, which can lead to hysterectomy and permanent infertility [6]. The uterus can also sustain structural damage from multiple surgeries, leading to infertility or subfertility. If not identified and treated quickly, this can cause severe bleeding, hemorrhagic shock, uterine rupture, and surgical complications, significantly raising the risk of maternal mortality [7]. As a result, the mortality rate for this type of pregnancy is approximately sevenfold higher than for other ectopic pregnancies [8].

CSP is categorized into two distinct types. The first involves implantation within the uterine cavity (type I, endogenous type), and the second invades a deep scar, extending to the bladder and abdominal cavity (type II, exogenous type) [9]. The endogenous type of CSP can result in a viable pregnancy but carries a high risk of placental site hemorrhage. Conversely, the exogenous variant is associated with uterine rupture and first-trimester bleeding [10]. To achieve the best results, it's crucial to diagnose and treat this condition early, so every pregnant woman with a history of cesarean section should undergo screening in the first trimester [11].

Recent clinical trials have examined treatment strategies for CSP, each with its own advantages and disadvantages. Medical treatment options include systemic and localized methotrexate (MTX) [12] and targeted potassium chloride (KCl) injection. MTX, a folate antagonist, is commonly used in the treatment of ectopic pregnancies due to its inhibition of cellular replication and DNA synthesis, which ultimately leads to the demise of the pregnancy [13]. Prior literature has demonstrated the effectiveness of intrauterine Methotrexate injection for managing a CSP, with high rates of effectiveness and treatment success. For instance, in the Yamaguchi study, nearly all patients were successfully treated, and a similar study reported complete resolution in all 45 CSP patients [14]. KCL has also been proposed as an effective CSP treatment; intrauterine injections of KCL cause cell death, induce fetal demise, and facilitate clearance of retained gestational tissue [15]. A conclusive approach is hysteroscopic surgery, wherein the gestational sac is resected via transcervical access under direct visualization via hysteroscopy [16]. This procedure allows for immediate and complete removal of the ectopic pregnancy and decreases the risk of residual trophoblastic tissue, and promotes more rapid restoration of the endometrium. However, hysteroscopic surgery requires specialized equipment and skills, limiting its overall use to specific clinical sites [17].

Considering the challenges of selecting the most effective treatment with minimal adverse effects, this study is a randomized controlled clinical trial assessing the efficacy of direct MTX injection into the GS, followed by curettage; direct KCL injection into the GS with curettage; and hysteroscopic resection (HRE), followed by intramuscular methotrexate (MTX IM) injection.