CSP is a long-term complication of cesarean section that carries a high-risk of uncontrolled hemorrhage. The incidence of CSP was reported from 1/1800 to 1/2216 in pregnancies, and account for 6.1% of all ectopic pregnancies in patients who had at least one cesarean section [
13]. Over the last 10 years, the incidence of CSP has been increasing because of the increased cesarean delivery rate and the advances of diagnosis in ultrasound and MRI [
3,
4]. However, there is still no consensus guideline for the management of CSP, more than 30 therapeutic schedules for patients with CSP, including systemic/ local administration Methotrexate (MTX), uterine artery embolization (UAE) followed by curettage, removal of the CSP transvaginal, laparoscopically or assisted by hysteroscopy have been reported [
14,
15]. Each of therapy has its own individual advantage and disadvantage. Yang H et al. found that methotrexate administration could significantly improve the curative effect of cesarean section patients with scar pregnancy by taking 160 patients with scar pregnancy as research subjects [
16]. However, methotrexate is not suitable for patients with high HCG levels or patients with fetal cardiac activity; Slow onset after initial administration; Causes complications such as bone marrow suppression and digestive system symptoms; The serum β-HCG level became negative for a long time. In another study, anhydrous ethanol chorionic villus targeting therapy was also an alternative option compared to methotrexate administration. Inject anhydrous ethanol into the sac directly could kill trophoblast cells, and level of β -HCG decreased significantly within a month [
17]. However, when anhydrous ethanol leaks into the abdominal cavity, peritoneal irritation occurs, causing hematoma around the pregnancy tissue. It has been reported that CSP resection under hysteroscopy is a safe and effective minimally invasive treatment. The hysteroscopy passes through the vagina into the uterus, visually identifying and scraping out pregnancy tissue. This method can cause little damage to the endometrium and has little impact on fertility [
18]. However, if the residual pregnancy tissue is still active, the persistent may lead to persistent ectopic pregnancy. Postoperative complications such as intrauterine adhesion, oligomenorrhea, even amenorrhea and menstrual bleeding can occur, which seriously affect the quality of life of patients [
19]. In the study of Pyra K et al., UAE was shown to be a safe and effective method with the advantages of timely hemostasis, low trauma and high success rate, and should be considered as an option for CSP treatment, especially for women who wish to maintain fertility [
20]. However, in another study, UAE caused platelet aggregation, fibrin deposition and thrombosis [
21]. In PyraK's follow-up study, a patient suffered from menstrual insufficiency, which may be due to utero-ovarian artery anastomosis. After uterine artery embolization, ovarian blood supply was affected, resulting in ovarian necrosis.
HIFU adopts a non-invasive method to ablate the pregnancy tissue, which causes the necrosis of the pregnancy tissue and is conducive to subsequent curettage, reducing the residual pregnancy tissue and reducing vaginal bleeding. After treatment, the patient's main complaint was lower abdomen or lumbosacral pain, which was relieved within 1 week without special treatment [
22]. In summary, HIFU treatment of CSP is safer and more effective than other methods. The ideal treatment strategy of CSP should meet the following criteria: safety, effectiveness, and/or a quick recovery of menstruation and fertility [
11]. To date, several researches reported and manifested that HIFU ablation was safe for patients with CSP, but there is no report the results about the different types patients of CSP [
5‐
8]. This study showed that the average time for gestational sac disappeared, vaginal bleeding of post-treatment, β-HCG level reduction to normal level, normal menstruation recovery and hospital stay were was not significantly different between CSP-Iand CSP-II. The safety of this non-invasive technique in the treatment of CSP patients is always a concern. Complication of HIFU ablation including skin burns in the treatment, fever,abdominal or pelvic pain, and distension-radiating pain into the lower limbs, have been described in reports on the experiment of treatment of uterine fibroids [
15,
23,
24]. In this study, immediately after HIFU ablation, the common adverse effect was lower abdominal or pelvic pain. There were no statistical differences in the adverse effects between the two groups. During the follow-up, nine patients became pregnant again. Fertility is affected by variety of factors including the maternal age, and ovarian reserve. Because of the small number of patients, the study did not analyze the potential factors in successful pregnancy after HIFU treatments in the two types CSP. The recovery of normal menstruation and conception during follow-up period of patients with CSP demonstrated that HIFU ablation combined with USg-D&C treatment for CSP has less adverse and is beneficial to retain the further fertility function. The great challenge in the treatment of HIFU ablation combined with USg-D&C for CSP is the anatomical position of the pregnancy lesion, where the myometrium of embryo implanted is thin or even defect and increasing risk of severe bleeding. There was a statistically significant difference in the thickness of myometrium in anterior lower uterine part between the CSP-Iand CSP-IIin the study. Compared with CSP-I, CSP-II has greater potential risks of severe bleeding. Zhu et al. have treated 53 patients with CSP with suction curettage under hysteroscopic guidance after HIFU ablation, and the median volume of blood loss in the procedure 20 ml [
7]. In a comparison study, Hong retrospective analyzed 152 CSP patients, who were treatment with HIFU ablation or UAE followed by hysteroscopy. Their results showed that blood loss was 76.38 ± 22.89 ml in the HIFU group, whereas it was 114.42 ± 30.34 ml in the UAE group. Zhang et al. reported that 25 CSP-II patients who were treated with transvaginal surgical management. The average intraoperative blood loss was 60.5 ml [
22]. The intraoperative blood loss of the CSP-Iwas significantly less than that of CSP-IIin this study, without hysterectomy and hemorrhage≥1000 ml. This result indicated that HIFU ablation followed by USg-D&C is safety in the CSP-Iand CSP-II, and it seems to be superior to UAE, and similar to transvaginal surgical management, but less invasive. Pregnancy in the scar from a cesarean delivery is located outside or inside of lower uterine cavity and is completely or partial surrounded by myometrium and fibrous tissue of the scar in the prior low uterine segment [
14]. Therefore, the scar surface of the lower anterior uterine wall may be deficient because of poor vascularity, fibrosis, and impaired healing. The objection of the management for CSP is to expel the pregnancy tissue in cesarean scar, decrease the sever bleeding risk. However, due to villus implanting in the muscular layer of lower uterine and lacking of effective shrinkage, directly curettage is not a first-line therapeutic option for CSP, because it could cause blood vessels rupture and catastrophic hemorrhage of uterus [
25]. How to effectively reduce the blood supply of pregnancy tissue before D&C is a current direction of CSP treatment. The application of HIFU ablation, a noninvasive technique, was approved by the U.S. Food and Drug Administration (FDA) and modified in2004 [
9]. The targeted tissue ablaion was achieved by instantaneous temperature elevation to 60–100°C, utilizing the physical characteristics of tissue penetration under the low-energy ultrasound waves which was produced by the HIFU treatment system [
8,
9]. According to literature reports, the advantages of HIFU ablation CSP may be as follows: 1) a rapid decline of β-HCG level and cessation of embryonic cardiac activity; 2) a reduction of blood flow in the trophoblast tissue ultrasound assessment; 3) an apparently decreased the risk of hemorrhage during the D&C procedure [
5‐
8,
22]. This study is limited because there is no international classification standard for CSP, and the special types of CSP have not been discussed in this research. It analyzed the safety and feasibility of HIFU ablation followed by USg-D&C for two types of CSP, but did not compare to other method, such as MTX or UAE. This study suggested that HIFU, a non-invasion treatment, can appear to be superior as it decreased the risk of hemorrhage during the D&C procedure for two types CSP, which is a single-center retrospective study and the multicenter and prospective studies be necessary to validate our findings in the future.