Cesarean scar pregnancy (CSP) refers to an ectopic pregnancy in which the fertilized egg implants at the site of a previous cesarean section scar. It is a time-limited definition, applicable only to early pregnancy. CSP is one of the long-term complications associated with cesarean deliveries. Due to the increasing rate of cesarean sections in recent years, the incidence of CSP has been rising. The underlying cause remains unclear but is thought to be related to poor healing of the uterine incision following a cesarean section, resulting in a wide scar or micro-defects. Inflammatory processes may also create tiny openings at the scar site. When the fertilized egg travels too quickly or develops too slowly through the uterine cavity, it may lack the ability to implant until reaching the scar, where it enters the myometrium through these micro-defects and implants.
Clinically, CSP is characterized by a history of a lower uterine segment cesarean delivery along with irregular vaginal bleeding following amenorrhea. It is often misdiagnosed as cervical pregnancy, inevitable abortion, or incomplete abortion. Occasionally, it is mistaken for a normal early pregnancy, leading to procedures such as induced abortion, which can result in massive hemorrhage or recurrent bleeding post-abortion. Because the myometrium in the lower uterine segment is relatively thin and the scar tissue from the cesarean incision lacks contractility, the ruptured vessels during miscarriage or curettage may fail to close spontaneously, causing life-threatening hemorrhage.
Transvaginal ultrasonography combined with color Doppler imaging is the primary diagnostic method for CSP. Typical ultrasound findings include:
- Absence of a gestational sac within the uterine cavity or cervical canal.
- A gestational sac located in the anterior wall of the uterine isthmus, with a visible yolk sac, embryonic bud, primitive cardiac activity, or a mixed echogenic mass.
- Significant thinning or disruption of the myometrium between the gestational sac and the serosal layer of the anterior uterine wall.
- Color Doppler flow imaging showing high-velocity, low-resistance blood flow signals surrounding the gestational sac.
Three-dimensional ultrasonography and magnetic resonance imaging (MRI) can further enhance diagnostic accuracy.
Given the high risks associated with CSP, termination of pregnancy is often recommended upon confirmation of the diagnosis. Treatment options include surgical and/or medical therapy. Surgery is the primary treatment method and is more effective than expectant management or medical therapy alone. Surgical techniques include ultrasound-guided suction curettage, hysteroscopic or laparoscopic CSP removal, and transvaginal anterior fornix incision for CSP removal. Individualized treatment should be determined based on gestational age, size of the gestational sac, the thickness of the thinnest myometrial layer at the scar site, and local blood flow conditions. Methotrexate (MTX) is the preferred medication, generally used as a preoperative adjunct; it is not recommended as a standalone therapy for CSP.
Indications for MTX therapy in CSP include:
- Patients unwilling or unsuitable for surgical treatment, with higher success rates observed in earlier pregnancies.
- Cases with residual trophoblastic tissue following surgery, where serum human chorionic gonadotropin (hCG) levels decline slowly, provided that the patient's vital signs are stable and no contraindications to MTX treatment exist.
Uterine artery embolization (UAE) is an effective adjunctive therapy. It is primarily employed as an emergency intervention for massive hemorrhage during termination of CSP or as a pre-treatment measure prior to curettage or lesion excision for CSP with a high risk of bleeding.
CSP can have variable clinical outcomes. If the patient and their family insist on continuing the pregnancy, full disclosure of the associated risks is necessary, and close monitoring is essential. In the event of complications, pregnancy termination should be promptly performed. In advanced pregnancy stages, placental implantation into the scar is common, necessitating thorough preparation before delivery.