Cesarean scar ectopic pregnancy is a complication in which an early pregnancy implants in the scar from a previous cesarean delivery. This condition presents a substantial risk for severe maternal morbidity and mortality because of challenges in securing a prompt diagnosis. Ultrasound is the primary imaging modality for cesarean scar ectopic pregnancy diagnosis, although a correct and timely determination can be difficult. Surgical, medical, and minimally invasive therapies have been described for cesarean scar ectopic pregnancy management, but the optimal treatment is unknown. Patients who decline treatment of a cesarean scar ectopic pregnancy should be counseled regarding the risk for severe morbidity. The following are the Society for Maternal-Fetal Medicine recommendations: we recommend against expectant management of cesarean scar ectopic pregnancy (GRADE 1B); we suggest that operative resection (with transvaginal or laparoscopic approaches when possible) or ultrasound-guided uterine aspiration be considered for the surgical management of cesarean scar ectopic pregnancy and that sharp curettage alone be avoided (GRADE 2C); we suggest intragestational methotrexate for the medical treatment of cesarean scar ectopic pregnancy, with or without other treatment modalities (GRADE 2C); we recommend that systemic methotrexate alone not be used to treat cesarean scar ectopic pregnancy (GRADE 1C); in patients who choose expectant management and continuation of a cesarean scar ectopic pregnancy, we recommend repeated cesarean delivery between 34 0/7 and 35 6/7 weeks of gestation (GRADE 1C); we recommend that patients with a cesarean scar ectopic pregnancy be advised on the risks of another pregnancy and counseled regarding effective contraceptive methods, including long-acting reversible contraception and permanent contraception (GRADE 1C).
The American College of Obstetricians and Gynecologists (ACOG) and the Society of Family Planning endorse this document. The American Society for Reproductive Medicine supports this document.
This document replaces SMFM Consult Series #49: Cesarean scar pregnancy (May 2020).
Introduction
Cesarean scar ectopic pregnancy (CSEP) is a complication in which an early pregnancy implants in the scar from a previous cesarean delivery. Perhaps because of high worldwide cesarean delivery rates, there seems to be increased incidence and recognition of this condition over the past 2 decades. The clinical presentation is variable, and many are asymptomatic at presentation. Patients may present to various obstetrical and gynecologic care providers, but maternal-fetal medicine subspecialists are often involved in the diagnosis and subsequent management of these pregnancies. CSEP can be difficult to diagnose in a timely fashion. Ultrasound imaging is the primary imaging modality for CSEP diagnosis. Expectantly managed CSEP is associated with high rates of severe maternal morbidity, such as hemorrhage, placenta accreta spectrum (PAS), and uterine rupture. Given these substantial risks, definitive surgical or medical management is recommended after CSEP diagnosis. Several surgical and medical treatments have been described for this disorder; however, optimal management remains uncertain at this time. For this reason, registries have been created for providers to submit data on diagnosis, natural history, and management ( https://csp-registry.com and https://octri.ohsu.edu/redcap/surveys/?s=XCK7FLEA84 ).
What is cesarean scar ectopic pregnancy, and what is its incidence?
CSEP occurs when an embryo implants in the fibrous scar tissue of a previous cesarean hysterotomy. This abnormal implantation presents a substantial risk of severe maternal morbidity and mortality complicated by challenges in securing a timely diagnosis and uncertainty regarding optimal treatment once identified.
Although relatively uncommon, reported international experience with CSEP seems to be increasing, likely because of high contemporary cesarean delivery volume. High cesarean delivery rates are observed in many of the world’s most populous developed nations, with an estimated 18.5 million women undergoing this procedure each year. Consequently, there is mounting collective awareness of rare cesarean delivery-associated complications such as CSEP.
The true incidence of CSEP is unknown because the condition is likely underdiagnosed and underreported. Reported single-center estimates of incidence range from 1 in 1800 to 1 in 2656 of overall pregnancies. , Although CSEP incidence is believed to have increased over time, other factors, including improved imaging with ultrasound and magnetic resonance imaging (MRI), increased use of transvaginal ultrasonography, and possibly increased physician awareness, may contribute to a perceived increase in incidence.
What is the pathogenesis of cesarean scar ectopic pregnancy?
Although the pathogenesis of CSEP is incompletely understood, the mechanism has been postulated to involve blastocyst implantation within a microscopic dehiscence tract in the scar from a previous cesarean delivery. Because of the fibrous nature of scar tissue, these inherently deficient implantation sites are at risk for dehiscence, PAS, and hemorrhage as the CSEP enlarges.
CSEP and placenta accreta seem to have similar disease pathways and may exist along a common disease continuum. In one series in which pregnancies complicated by either CSEP or early PAS underwent histopathologic analysis by blinded pathologists, findings were indistinguishable between groups, with a high interobserver correlation. Histopathologic analyses for both groups were characterized by myometrial or scar tissue villous invasion with little or no intervening decidua.
The implantation patterns of CSEP can be categorized as either endogenic (also referred to as “on the scar”) or exogenic (“in the niche”). , Endogenic is defined as growing within the uterine cavity and exogenic as arising from a deeply implanted gestational sac into the scar that may grow toward the bladder or abdominal cavity. These ultrasonographic appearances may influence obstetrical prognosis. , It has recently been suggested that early first-trimester determination of whether a CSEP is growing “on the scar” or “in the niche” of the previous cesarean hysterotomy may be used to predict subsequent pregnancy outcome , ( Figure 1 ). In one small retrospective study, patients with pregnancies growing “on the scar” had variable obstetrical outcomes, whereas those with pregnancies growing “in the niche” all underwent hysterectomy with PAS at delivery.
How does cesarean scar ectopic pregnancy present clinically, and are there known risk factors?
Although second-trimester diagnoses have been reported, CSEP usually presents in the first trimester. In one review of published CSEP case series, the average gestational age at diagnosis was 7.5±2.5 weeks. The clinical presentation is variable, ranging from asymptomatic ultrasonographic detection to a presentation with uterine rupture and hemoperitoneum, typically in the absence of a timely diagnosis. In the previously mentioned review, approximately one-third of cases were asymptomatic, and approximately one-third presented with painless vaginal bleeding. Nearly one-quarter of presentations involved pain, with or without bleeding. Patients with ruptured CSEP may also present with hemodynamic collapse.
Although by definition previous cesarean delivery is a prerequisite for CSEP development, and placenta previa may modify this risk, it is not clear if the number of previous cesarean deliveries further increases the risk. Notwithstanding that some reports and anecdotal observations suggest an overrepresentation of women with multiple previous cesarean deliveries in CSEP cohorts, a review of the literature reveals that 52% of CSEP cases occur in women with a single previous cesarean delivery. , , Interestingly, the indication for previous cesarean delivery may be a risk factor for CSEP, with previous delivery for breech presentation seeming to be a more common indication in women who later experience CSEP. , , , It is hypothesized that the lower uterine segment is often less well developed in pregnancies that are delivered for malpresentation, and that a thicker hysterotomy scar presents a greater risk of poor healing and resultant microscopic dehiscence. No published data exist regarding an association between the hysterotomy closure technique and CSEP.
How is cesarean scar ectopic pregnancy diagnosed?
Ultrasound imaging is the primary imaging modality for CSEP diagnosis, although a correct and timely determination can be difficult. The initial finding of a low, anteriorly located gestational sac should raise concern for a possible CSEP and warrants further investigation. When patients with suspected CSEP are evaluated, a high degree of clinical suspicion is needed because a missed or delayed diagnosis can result in uterine dehiscence, hemorrhage, loss of fertility, or maternal death.
Transvaginal ultrasound imaging is the optimal modality for the evaluation of suspected CSEP because it provides the highest image resolution ( Figures 2 and 3 ). Grayscale combined with color Doppler ultrasound imaging is recommended for CSEP diagnosis. One group suggests combining transvaginal ultrasound imaging with a transabdominal ultrasonogram with a full maternal bladder to provide a “panoramic view” of the uterus and the relationship between the gestational sac and bladder. Although test performance characteristics are unknown and likely influenced by examiner experience and skill, in one review, 94 of 111 (84.6%) CSEP cases were detected by transvaginal ultrasound imaging, with the remaining 17 (15.4%) pregnancies incorrectly diagnosed as incomplete abortions or cervical pregnancies.
Since diagnostic criteria were first proposed by Vial et al in 2000, other authors have suggested modifications to enhance the ultrasonographic detection of CSEP. , One approach proposes the following ultrasonographic criteria to diagnose CSEP: (1) an empty uterine cavity and endocervix; (2) placenta, gestational sac, or both embedded in the hysterotomy scar; (3) a triangular (at ≤8 weeks of gestation) or rounded or oval (at >8 weeks of gestation) gestational sac that fills the scar “niche” (the shallow area representing a healed hysterotomy site); (4) a thin (1–3 mm) or absent myometrial layer between the gestational sac and bladder; (5) a prominent or rich vascular pattern at or in the area of a cesarean scar; and (6) an embryonic or fetal pole, yolk sac, or both, with or without fetal cardiac activity ( Figure 4 ). All of these criteria may not be observed. Especially with very early diagnosis and before fetal cardiac activity, the patient should have confirmation of pregnancy (for example, a positive pregnancy test result). Bulging or ballooning of the lower uterine segment in the midline sagittal transabdominal view has also been considered to be supportive of CSEP diagnosis. ,
A challenge in the diagnosis of CSEP is distinguishing it from other clinical entities with a similar ultrasonographic appearance. In a literature review that collected 751 cases of CSEP, 107 (13.6%) cases were originally misdiagnosed as cervical ectopic pregnancies, spontaneous abortions in transit, or low implantation of an intrauterine pregnancy. Given the importance of prompt diagnosis, referral to an experienced center for a second opinion may be preferable to ongoing follow-up examinations that are likely to delay diagnosis.
Are other modalities useful for the diagnosis of cesarean scar ectopic pregnancy?
Transvaginal 3-dimensional ultrasound and 3-dimensional power ultrasound imaging have been used in an attempt to enhance the accuracy of CSEP diagnosis, with case reports supporting the utility of these techniques. However, because of limited published experience with these approaches, there are insufficient data to support a benefit of routine use of 3-dimensional ultrasound imaging for the diagnosis or management of CSEP.
MRI has been used as an adjunct to ultrasound imaging for the diagnosis of CSEP, although its incremental benefit over ultrasound imaging alone is unknown. , , , Both T1- and T2-weighted images can demonstrate a gestational sac embedded within the lower uterine segment at the level of a previous cesarean scar niche and an empty endometrial cavity and endocervix. In one MRI series, most CSEPs presented as a thin-walled diverticulum at the cesarean scar niche. MRI may also provide useful information regarding the degree of invasion and whether there is evidence of PAS. Most authors do not recommend MRI as a routine component of CSEP evaluation because transvaginal ultrasound imaging with color Doppler interrogation is believed to be reliable in securing a correct diagnosis. However, in cases in which ultrasound imaging is inconclusive, MRI could be considered as an adjunct study. Given the risks associated with delayed diagnosis, the use of multiple ultrasound imaging approaches and modalities, such as MRI, is likely preferable to serial ultrasound examinations.
CSEP diagnosis has been reported with the use of hysteroscopy and laparoscopy. , , , Although these methods are not recommended solely for diagnostic purposes, they can be used to confirm a diagnosis at the time of planned operative intervention. With laparoscopic examination, CSEP has been described as an ecchymotic bulge with a “salmon-red” appearance beneath the bladder at the level of the previous cesarean scar with an otherwise normal-appearing uterus. ,
What is the natural history of cesarean scar ectopic pregnancy?
Limited information exists regarding the natural history of CSEP because few recognized CSEPs continue to a viable gestational age. Those that do are believed to be at high risk for severe complications in the second and third trimesters, although the rates of these complications are unknown. CSEPs have resulted in live births, often associated with PAS, cesarean hysterectomy, and massive hemorrhage at delivery. , , Series describing outcomes of expectantly managed CSEPs all involve small case numbers and high hysterectomy rates that range from 50% to 100% and are usually associated with PAS. , In case series of women who were treated expectantly, most required additional treatment, and >50% had severe complications. In one series that prospectively followed up 10 women with a first-trimester ultrasonographic diagnosis of a pregnancy implanted in or on a previous cesarean scar, all the women had PAS diagnosed at the time of the repeated cesarean delivery.
Because of the high risk of severe maternal morbidity, expectant management is not recommended for a recognized CSEP, and definitive surgical or medical management generally is advised as soon as the diagnosis is confirmed. , , For cases where CSEP is suspected but the diagnosis is not certain, short-interval follow-up, a second opinion, or additional imaging with MRI should be considered to establish a timely diagnosis without undue delay. We recommend against expectant management of CSEP (GRADE 1B).
An exception to the recommendation against expectant management involves early CSEP characterized by fetal death or other evidence of early pregnancy failure. In the case of an early CSEP that is definitively diagnosed as nonviable, expectant management may be pursued with serial ultrasound surveillance, quantitative human chorionic gonadotropin (hCG) measurements, and monitoring for maternal symptoms such as bleeding or pelvic pain. However, it should be recognized that it can take several months for a nonviable CSEP to resolve spontaneously, and expectant management of nonviable CSEPs has been associated with the development of a uterine arteriovenous malformation (AVM). Uterine AVM in this clinical context has been associated with persistent, severe vaginal bleeding and may require umbilical artery embolization or even hysterectomy. In a series by Timor-Tritsch et al, 20% (2/10) of expectantly treated women had an AVM.
What cesarean scar ectopic pregnancy treatment modalities have been reported?
Although many different options for the management of CSEP have been reported, the optimal treatment is unknown ( Table ). Surgical, medical, and minimally invasive therapies and various combinations of such treatments have been described. However, the medical literature consists predominantly of case series, with a limited number of randomized controlled trials comparing treatment approaches. These series are influenced by variable levels of clinical experience, institutional capability, provider skill, and case complexity, which hinders comparisons between studies. Conclusions regarding optimal CSEP therapy are further limited by a lack of head-to-head comparisons between medical and surgical approaches.
| Method | Number of studies | Number of patients | Efficacy, % a | Complications b | |
|---|---|---|---|---|---|
| Case series | RCTs | ||||
| Expectant management | 5 | 0 | 41 | 41.5 | 53.7% |
| sMTX | 18 | 3 | 339 | 75 | 13% |
| Needle aspiration+sMTX | 6 | 0 | 148 | 84.5 | 15.5% |
| D&C | 21 | 0 | 243 | 48 | 21% |
| Hysteroscopy c | 7 | 0 | 95 | 83 | 3.2% |
| Transvaginal resection d | 6 | 0 | 118 | >99 | 0.9% |
| UAE+D&C | 5 | 2 | 295 | 93.6 | 3.4% |
| UAE+D&C+hysteroscopy | 1 | 1 | 87 | 95.4 | 1.2% |
| UAE+D&C+sMTX | 13 | 1 | 427 | 68.6 | 2.8% |
| Local and sMTX | 2 | 0 | 34 | 75 | 2.3% |
| Laparoscopy | 7 | 0 | 69 | 97.1 | 0 |
| Local MTX | 2 | 1 | 74 | 64.9 | 4.1% |
| HIFU | 1 | 0 | 16 | 100 | 0 |
| HIFU+hysteroscopic suction curettage | 1 | 0 | 52 | 100 | 0 |
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