The overall incidence of ectopic pregnancy in the first trimester is approximately 1–2%, and ectopic pregnancy rupture accounts for approximately 2.7% of pregnancy-related deaths . The most common form of ectopic pregnancy encountered in the clinic is fallopian tube pregnancy. Cervical pregnancy, ovarian pregnancy, CSP, and other locations of ectopic pregnancy are relatively rare. Ectopic twin pregnancy is extremely rare clinically, with an incidence of approximately 1/125,000 reported in the literature. There are comparatively more reports of ectopic twin pregnancy in the same or contralateral fallopian tubes, and it is more commonly seen after assisted reproduction [3, 4]. There are also some reports of ovarian ectopic twin pregnancy , cornua uteri ectopic twin pregnancy , and CSP associated with cornua uteri ectopic pregnancy . The current case was particularly rare because it was a spontaneous CSP associated with ectopic tubal twin pregnancy, of which only one case has been reported to date . According to existing reports of ectopic twin pregnancy, CSP lacks specific clinical symptoms compared with other ectopic pregnancies. Menopause, irregular vaginal bleeding, and abdominal pain are the main symptoms, and the diagnosis mainly relies on ultrasound examination. Due to its low incidence, ectopic twin pregnancy can easily be missed or misdiagnosed.
Improper treatment of CSP can lead to massive bleeding, uterine rupture, and uterine resection, the results of which can be life-threatening. Accordingly, CSP attracts a high degree of attention from obstetricians and gynecologists. Early diagnosis, early termination of pregnancy, and early treatment are the primary principles of CSP treatment . To date the precise etiology of CSP remains unclear. Some scholars have proposed a theory involving a uterine incision defect, in which cesarean section causes endometrial injury, incision edge dislocation, or incision infection. Such situations can easily lead to poor healing of a cesarean section incision and a uterine incision defect conducive to zygote implantation. If the endometrium is not decidualized, gestational trophoblast cells can directly invade the myometrium. Studies indicate that independent risk factors for CSP include maternal age > 35 years, more than three pregnancies (particularly more than five), more than two induced abortions (particularly more than five), < 5 years between pregnancy and previous cesarean section (particularly < 2 years), and a history of induced abortion after cesarean section . Chen et al.  reported that elective cesarean section before labor is an independent risk factor for uterine incision defect after cesarean section. This may be related to poor formation of the lower uterine segment, poor selection of the incision location, poor drainage of uterine blood due to a non-dilated cervix, and/or increased uterine pressure affecting healing of the incision. The present 36-year-old patient’s history included a cesarean section in 2014 and three induced abortions, and the current presentation involved her fifth pregnancy. We speculated that the naturally conceived ectopic twin pregnancy may have been related to the patient’s history of cesarean section, multiple induced abortions, and pelvic adhesion.
The classification of CSP is closely related to the selection of treatment methods and prognosis, but to date there is no recognized optimal classification method. In a 2016 expert consensus on the diagnosis and treatment of CSP it was classified as type I, II, or III based on the direction of growth of the gestational sac implanted at the scar, and the thickness of the myometrium between the bladder and gestation sac as determined via ultrasound . It is widely accepted that ultrasound is the preferred diagnostic method for CSP, but MRI can clearly depict the relationship between the pregnancy sac and the uterus associated with surrounding organs.
CSP is often mistaken for cervical pregnancy, unavoidable abortion, or incomplete abortion in clinical practice. In the current case B-ultrasonography combined with MRI showed that: (1) a pregnancy sac was partially implanted in the uterine scar and partially located in the uterine cavity; (2) there was obvious deformation of the gestational sac; (3) the myometrium between the pregnancy sac and the bladder was thinned, with a thickness of approximately 7 mm; (4) there was trophoblast blood flow signal in the scar of the uterus; (5) abnormal hypoecho was detected in the left adnexal area, with yolk sac, germ, and primitive cardiac tube pulsation. Based on examination results the CSP was considered to be type I associated with left tubal pregnancy.
Treatments for tubal pregnancy mainly include expectant treatment, drug treatment, and surgical treatment. In the present case fetal heart pulsation was observed in the sac in the left fallopian tube, so laparoscopic exploratory surgery was planned. More than 30 CSP treatments have been reported, but the main treatment options include drug therapy (e.g., systemic or local methotrexate therapy), surgical therapy (including uterine curettage, removal of pregnancy and uterine scar repair, hysterectomy), uterine artery embolization (UAE), and combined therapy . Expectant therapy is generally not recommend for CSP. Maheux-Lacroix et al.  reported that expectant therapy resulted in 57% live births, but approximately 63% of women required a hysterectomy because of placental implantation or uterine rupture in the second trimester. Kaelin Agten et al.  investigated 17 CSP patients from two centers and divided them into two groups based on the location that scar pregnancies implanted as determined via first-trimester ultrasound; “on the scar” (group A, 6 cases) and “in the niche” (group B, 11 cases). In group A only one patient underwent cesarean-hysterectomy due to placenta implantation, whereas the other 5 patients delivered via normal cesarean section. In group B 10 patients underwent hysterectomies after cesarean section due to placenta implantation, and 1 patient underwent hysterectomy due to massive hemorrhage at 20 weeks of pregnancy. In further analysis women with a thickness of less than 2 mm between the musculature of the gestational sac and the bladder in first-trimester ultrasonography were more likely to have placental implantation. If the embryo grows into the scar and protrudes to the bladder the pregnancy needs to be terminated because the outcome of continuing the pregnancy is uterine rupture, or even placenta bladder implantation. The risk and difficulty of the operation increase with gestational age. If the CSP is implanted on the scar, and the muscle layer between the bladder and the embryo is relatively complete, the embryo villus has no obvious muscular infiltration. In such cases it needs to be made clear to the patients and their families that if they choose to continue the pregnancy potentially dangerous placenta previa may occur in the future, which would greatly increase the risk of postpartum hemorrhage and even uterine resection.
Clinical drug therapies for CSP mainly include methotrexate combined with uterine artery embolization, ultrasound-guided local injection of methotrexate into the pregnancy cyst, and systemic injection of methotrexate. Such treatments can fail however, necessitating surgical treatment such as UAE or even hysterectomy for massive bleeding. Some reports indicate that a second treatment is not required if the CSP patient undergoes drug treatment before 7 to 8 weeks of pregnancy because this results in less bleeding, but such patients require a longer recovery time. If medication is used blood flow signals around the pregnancy sac and blood HCG should be detected, and CSP-associated extreme enhanced myometrial vascularity, which is high flow and low-obstruction blood flow around the residual pregnancy sac or placenta, often requires one or more UAEs and even hysterectomy . Blood HCG is assessed once a week, and a reduction of > 15% each time is considered to indicate effectiveness . For CSP without a yolk sac and fetal heartbeat, ultrasound and blood HCG follow-up can be considered, or systemic methotrexate can be administered . Some studies indicate that the success rate of systemic methotrexate for CSP (≈ 62%) is significantly lower than that of tubal pregnancy (≈ 90%), which may be related to the fact that the fibrous tissue surrounding the implantation of the embryo in the uterine scar reduces the absorption of methotrexate .
Uterine curettage can be considered for type I CSP with stable vital signs and a gestational age of less than 8 weeks, but direct uterine curettage is not recommended. Pregnancy should be removed under B-ultrasound surveillance or hysteroscopy, and preparations for hemostasis and UAE should be made. There is currently no conclusive evidence of differences between hysteroscopic uterine curettage and ultrasonographic uterine curettage with respect to success rate, intraoperative or postoperative complications, adverse reactions, or β-HCG normalization time . For type II and III CSP and type I CSP with a gestational age of > 8 weeks, preventative UAE should be performed before uterine curettage . In a retrospective analysis of 232 women with CSP the success rate of uterine curettage before 7 weeks of pregnancy was approximately 91%, significantly higher than the 56% success rate of uterine curettage after 7 weeks . Reports suggest that UAE is currently the most widely used CSP treatment, but efficacy and outcomes differ across studies . Studies have also shown that UAE is associated with reduced ovarian function, intrauterine adherence, reduced pregnancy rate, and increased abortion rate . Hence, some scholars have suggested that UAE should only be used in situations in which there is a high risk of bleeding, including older gestational age or ultrasound depicting abundant blood flow or massive vaginal bleeding . The value of UAE for the treatment of CSP requires further study.
For type II and III CSP, surgical resection of pregnancy tissue and scar repair therapy are recommended because of the associated high success rate, rapid recovery, and minimal effect on fertility . The operative methods include traditional transabdominal, laparoscopic, and transvaginal surgery. Studies indicate that surgical resection and defect repair have a high success rate (≥ 96%) and entail a low risk of bleeding (≤ 4%) . Because of the substantial trauma associated with transabdominal surgery it is generally only used for the emergency treatment of massive bleeding in CSP. Laparoscopic surgery has been widely used because it is associated with less trauma. Above all, laparoscopic surgery requires skilled operators and equipment conditions. If intraoperative bleeding is excessive and hemostasis is difficult to achieve, it must immediately be converted to transabdominal surgery. In 2011 Kang et al.  reported transvaginal resection of pregnancy tissue and scar repair for the first time. More than 200 cases of the procedure have since been reported, suggesting that transvaginal surgery is less invasive, has a higher success rate, and is associated with a lower rate of hysterectomy . In the current patient the CSP was complicated by left tubal pregnancy, thus a decision to perform laparoscopic surgery was made, and preparations for blood reserves, UAE, and a transition to transabdominal surgery were also put in place. After intraoperative separation of adhesions, weak tissues were evident at the cesarean scar and a purplish blue swelling of approximately 4 x 3 cm was observed. Therefore, we decided to conduct laparoscopic removal of the pregnancy at the uterine scar and uterine scar repair during the operation. At the same time, in order to reduce intraoperative bleeding we injected hypophysis into the uterus to promote contractions. The amount of intraoperative bleeding was approximately 50mL. The patient recovered well after surgery, and blood HCG returned to a normal level during outpatient follow-up. Because she had no requirement for fertility, we recommended diligent contraception.
It is difficult to conduct well-designed randomized controlled multicenter CSP studies because of its low incidence. There are no well-established treatment guidelines, and the results of many existing treatments differ across different studies. The present case of spontaneous caesarean scar associated with ectopic tubal twin pregnancy was successfully treated via laparoscopic surgery. The case emphasizes the benefits of early diagnosis and treatment of ectopic pregnancy. During the process of diagnosis and treatment of patients with vaginal bleeding, abdominal pain, and other symptoms ectopic pregnancy should be strongly suspected, and the possibility of twin ectopic pregnancy should be borne in mind in order to avoid missed diagnosis.