Cesarean Scar Pregnancy: Diagnosis and Pathogenesis

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Key points

  • Cesarean scar pregnancy (CSP) is a potentially dangerous, man-made consequence of a previous cesarean delivery (CD).

  • CSP and placenta accreta spectrum (PAS) share the same histologic picture. CSP is a precursor of PAS.

  • Most patients with a CSP diagnosed in the first trimester that reach the third trimester of pregnancy have the potential to deliver a liveborn infant via repeat CD, almost all have different degrees of PAS, and in most cases will have hysterectomy.

  • The best diagnostic tool is

Nomenclature and terms

Various terms were and are still used for CSP, such as “cesarean ectopic pregnancy,” “cesarean scar ectopic,” “ectopic,” “isthmocele,” and “cesarean delivery scar pregnancy.” Here we use the term cesarean scar pregnancy. The two main reasons are: CSP is not an ectopic gestation because, if left to continue, it expands/morphs into an intrauterine pregnancy; and treatments usually used for what are considered “real” ectopic pregnancies (tubal, cornual, interstitial, and cervical) cannot be

Background

The occurrence of CSP is closely related to a previous CD. In the United States the rate of CD estimated in 2017 was 32.0%.2 The cesarean section rate is lower today. The Centers for Disease Control and Prevention reveals that the overall rate of cesarean section births have stopped increasing and steadied at 32% from 2009 to 2011.3

Incidence

The true incidence of CSP is unknown. Almost all articles and related articles quote the only available estimates that the range is from 1/1800 to 1/2500 of all CD performed.4, 5 One can expect an increase of the reported incidence caused by increased awareness and the more accurate diagnosis of this entity.

Risk factors for cesarean scar pregnancy

The only risk factor for CSP is one or more previous CDs.

Pathogenesis

During a normal pregnancy the trophoblast penetrates the myometrium and remodels the vascular bed to enable a low-resistance/high-velocity blood flow to the conceptus. This physiologic “invasion” is stopped by the Nitabuch fibrinoid layer, a layer of fibrin (fibrinoid material) between the boundary zone of compact endometrium and the cytotrophoblastic shell in the placenta. This layer is naturally present between the endometrium in normally attached placentae. Previous uterine surgery or

What is the cesarean scar pregnancy?

CSP occurs when a blastocyst implants in a microscopic or macroscopic tract on the uterine scar or in the “niche” (or dehiscence) left behind by an incision site of the previous CD. The mechanism is the same after uterine surgery (curettage, myomectomy, endometrial ablation, manual removal of placenta, or any intrauterine surgical manipulation) with one significant difference: the latter causes are extremely rare (Fig. 1A, B).

The difference between the “on the scar” and “in the niche”

What is a niche of a previous cesarean section?

The niche or dehiscence is a discontinuity of the low anterior uterine wall seen after the healing process of a previous CD. At times a thick scar forms without leaving behind a defect, other times a usually triangular defect is visible either on an unenhanced ultrasound (US) or highlighted by a saline infusion US examination.8, 9

It should be realized that regardless of the size or measurements of the niche on the sagittal uterine sections, a transverse/coronal section may reveal the actual

Clinical presentation of cesarean scar pregnancy

As in every intrauterine pregnancy vaginal bleeding of different degrees may be the first sign of a CSP. Pain is usually not a typical presenting symptom. Patients may be asymptomatic and only become aware of a CSP when detected by US. The initial and early US between 5 and 7 weeks is critical because many CSPs are misdiagnosed as threatened abortion, miscarriage, or simply intrauterine pregnancies. Misdiagnoses may lead to curettage for a presumed failed pregnancy causing profuse bleeding and

Diagnosis of cesarean scar pregnancy

Every woman who presents in the first trimester to the obstetrics/gynecology practitioner with a positive pregnancy test and a history of a previous CD should be considered a CSP until proven otherwise.

The best and first-line imaging modality to diagnose a CSP is transvaginal US (TVUS). It presents a clear advantage over the transabdominal imaging. In some articles the authors used MRI for the diagnosis. Our view is that TVUS provides the precise diagnosis in almost all cases without the need

Differential diagnosis of cesarean scar pregnancy

The differential diagnoses of CSP are: cervical pregnancy and a miscarriage in progress “caught” in transition, close to the internal os or the cervical canal. It should be stressed that cervical pregnancies are rare and most importantly usually do not occur in patients with previous CDs. Miscarriages on their way to be expelled from the uterus do not have an actively beating heart. In the case of a sac on its way out, the exerting pressure on the uterus with the vaginal probe results in

Is there a placenta accreta spectrum in the first trimester of pregnancy?

Several articles suspected that there is pathologically implanted placenta in the first trimester. However, the first reliable publication on the subject was Comstock and colleagues.13 More than a decade later articles by Rac and colleagues,14 D’Antonio and colleagues,15 and Cali and colleagues16 (three articles) reported that there are sonographic markers of PAS in the first trimester and they can be recognized at different gestational ages.

The following is a list of the sonographic

Natural history of cesarean scar pregnancy

It is to be expected that several early, first trimester CSPs spontaneously demise much like some intrauterine gestations, of which approximately 15% do so. However, the exact number of spontaneously failing CSPs is unknown. A reasonable speculation is that this may be at least the rate of those in utero considering that the implantation site may not be the most favorable environment for a scar pregnancy. Some patients may elect termination of the pregnancy after evidence-based counseling to

Does the distance between the gestational sac and the anterior uterine surface/bladder predict outcome?

In the last few years based on clinical impression and increasing experience, clinicians started to evaluate if a deeply embedded gestational sac and placenta “in the niche” or dehiscence results in a more ominous outcome than if it is implanted “on the scar” (discussed previously).

Recurrent, heterotopic, and multiple cesarean scar pregnancies

Reviewing the pertinent literature published through 2011 we identified seven recurrent cases of CSP.11 Ben Nagi reported a 5% rate of recurrent CSP among 21 pregnancies after prior conservatively managed CSP.26

Bennett and colleagues27 and our group reported of a single patient with five recurrent CSPs. After the first four live CSPs were injected with local intragestational methotrexate, the last delivered near term with repeat CD and total abdominal hysterectomy for MAP.

Sadeghi and coworkers28

Pregnancy following treatment of cesarean scar pregnancy

There are no reliable articles dealing with this issue. However, compiling the clinical information on the 751 cases of CSP we found descriptions of 64 intrauterine pregnancies after first trimester treatment of CSPs.11 Pregnancies and deliveries after CSPs may be underreported. Wang and colleagues41 reviewed 32 cases of CSP. Seven had subsequent pregnancies.

Ben Nagi and coworkers42 published probably the largest series of reproductive performance of women after a history of CSP. They followed

Short cesarean-to-pregnancy interval: is it a risk factor for subsequent cesarean scar pregnancy

Only indirect information is available in the literature. It was suggested that short pregnancy intervals contribute to development of placenta accreta. A case-control study of uterine scar failures among laboring patients with previous low transverse CD was published with special attention to their interpregnancy interval (IPI). An IPI of less than 6 months was significantly more prevalent among case patients with uterine scar failure (P = .02). Mean IPI interval was less in all cases of

Summary

  • 1.

    CSP is a complication-ridden, potentially dangerous clinical entity. Its occurrence rate is closely related to that of CDs.

  • 2.

    The best diagnostic tool is TVUS. Grayscale and color Doppler US provide satisfactory diagnostic information. MRI is not necessary for making an accurate diagnosis. Every patient with previous CD should be screened for CSP. A patient with previous CD and low anterior gestation is CSP unless proven otherwise.17

  • 3.

    CSP and PAS share the same histologic picture. CSP is a precursor

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    Nothing to declare.

    1

    Present address: viale Acacie 26, Casteldaccia, Palermo 90014, Italia.

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