Abstract
Introduction
Prenatal diagnosis of placenta accreta spectrum (PAS) depends on reliable ultrasound markers and skilled image interpretation. Existing PAS markers emphasize placental features suggestive of abnormal adherence and require advanced image optimization. However, emerging hypotheses suggest that uterine dehiscence—not placental invasion—is the central mechanism underlying PAS, particularly in severe (Grade 3) disease. Despite this, few established ultrasound markers address this uterine dehiscence. We describe a novel ultrasound marker, the taper sign, which uniquely represents the uterine dehiscence in severe PAS with anterior placenta previa, and outline a standardized technique for image acquisition and interpretation.
Methods
This descriptive report details the sonographic appearance of the taper sign on grayscale ultrasound in pregnancies with anterior placenta previa and prior cesarean delivery with surgically and histopathologically confirmed Grade 3 PAS. Ultrasound images from cases at our center were reviewed to characterize the morphologic features of the taper sign and define optimal imaging parameters. Representative images illustrate this novel marker and the required anatomical landmarks.
Results
The taper sign is characterized by progressive myometrial thinning until it disappears at the level of the prior cesarean scar, producing a wedge‐shaped appearance; this is distinct from previously described PAS markers. It is best seen using transvaginal ultrasound with a partially full bladder. Beginning in a midsagittal 2D grayscale view of the cervix, the anterior cervical lip is traced proximally as it transitions into the lower uterine segment myometrium. With the placenta previa bulging anteriorly, the overlying myometrium tapers to a point, terminating at the margin of the uterine dehiscence. This correlates with the deepest placental infiltration seen in Grade 3 PAS. In our experience, the taper sign is easily obtained and consistently identified in Grade 3 PAS with anterior placenta previa and prior cesarean delivery.
Conclusion
The taper sign represents a novel ultrasound marker of severe PAS, reflecting the distinct wedge‐like appearance of attenuated myometrium as it terminates at the uterine dehisence. This report provides a standardized description and imaging protocol to facilitate recognition of patients at increased risk for severe maternal morbidity. Ongoing studies aim to validate this marker's diagnostic performance.
Keywords: abnormal placentation, abnormally invasive placenta, increta, morbidly adherent placenta, percreta, placenta accreta spectrum, placenta previa
1. INTRODUCTION
Placenta accreta spectrum (PAS), the clinico‐pathologic diagnosis of deeply implanted placenta within or beyond the myometrium, is an increasingly common cause of severe maternal morbidity and mortality [1]. Complications include hemorrhage, coagulopathy, hysterectomy, massive transfusion, surgical injury, intensive care unit admission, and death. Patients with placenta previa and prior cesarean delivery have the highest risk, increasing from 3% with no prior cesareans to 11%, 40%, 61%, and 67%, with one through four prior cesareans, respectively [2].
Historically, PAS was attributed to abnormal placental invasion into and beyond the uterine wall. This theory underpins the International Federation of Gynecology and Obstetrics (FIGO) classification system, in which Grade 1 represents superficial attachment, Grade 2 represents invasion into but not through the myometrium, and Grade 3 represents deep invasion through the myometrium and beyond [3]. Grade 3 PAS carries the highest maternal morbidity risk, making prenatal identification essential for multidisciplinary planning [1, 4].
Prenatal ultrasound is the preferred diagnostic tool for PAS [5]. Current ultrasound markers emphasize placental features suggestive of abnormal adherence, including lacunae, loss of the retroplacental clear zone, bladder wall interruption, placental bulge, exophytic mass, and bridging vessels [5]. Many of these require advanced image optimization and expert interpretation, and demonstrate variable reproducibility.
Emerging pathophysiologic models increasingly support uterine dehiscence at the prior cesarean scar—rather than true placental invasion—as the central mechanism underlying PAS, particularly in severe (Grade 3) disease [6, 7]. This concept reframes PAS as a disorder of uterine wall integrity with secondary placental herniation and deep adherence into areas of myometrial deficiency [3]. Despite this paradigm shift, existing ultrasound markers continue to focus on placental morphology, and aside from placental bulge and myometrial thinning, no established marker specifically represents uterine dehiscence [5].
We describe a novel ultrasound marker, the taper sign, which reflects the uterine dehiscence in severe PAS with anterior placenta previa and prior cesarean delivery. This descriptive technical report aims to define the sonographic appearance of the taper sign and outline a standardized technique for its acquisition and interpretation.
2. MATERIALS AND METHODS
This descriptive technical report characterizes the taper sign on prenatal ultrasound in pregnancies with anterior placenta previa, prior cesarean delivery, and surgically and histopathologically confirmed Grade 3 PAS. We retrospectively reviewed ultrasounds for cases diagnosed and delivered at our tertiary PAS referral center over 19 months.
At our center, patients with placenta previa and prior cesarean undergo systematic transvaginal ultrasound evaluation by perinatologists with PAS expertise. Magnetic resonance imaging is not routinely performed.
Ultrasound examinations were performed using GE Voluson E8/E10 systems (GE Healthcare) with endocavitary transducers (5–9 MHz). Images and cine loops were reviewed to identify consistent morphologic features of the taper sign and define optimal imaging conditions. Representative images illustrate the taper sign and relevant anatomic landmarks. Here, we present a descriptive and technical report; diagnostic performance metrics were not assessed. Institutional review board approval was obtained with waiver of informed consent.
3. RESULTS
3.1. Description of the taper sign
The taper sign is characterized by progressive myometrial narrowing beneath a prior cesarean scar, producing a wedge‐like configuration that tapers and ultimately disappears as it approaches the uterine serosa. This reflects the attenuated lower uterine segment myometrium at the distal margin of the uterine dehiscence. Unlike myometrial thinning, which represents a single‐point measurement, the taper sign describes the dynamic geometric configuration as the myometrium progressively narrows toward complete dehiscence.
3.2. Imaging technique
The taper sign is best visualized using transvaginal ultrasound with the patient in lithotomy position and bladder partially full, allowing optimal delineation of the lower uterine segment, uterocervical junction, and uterovesical interface. Imaging begins in the midsagittal plane using two‐dimensional grayscale ultrasound.
Starting with a standard cervical view, the anterior cervical lip is followed cephalad as it transitions into the lower uterine segment myometrium. With an anterior placenta previa and prior cesarean scar, the overlying myometrium progressively tapers, terminating abruptly at the point of uterine dehiscence, producing the characteristic triangular wedge‐like appearance of the taper sign (Video S1, Figure 1). This is readily appreciated on grayscale imaging with minimal optimization, similar to standard cervical length assessment. Color Doppler demonstrates the hypervascularity and neovascularization of engorged vessels along the anterior lower uterine segment (Video S2). Adjusting the depth, magnification, and focal zone at the level of the prior cesarean scar enhances visualization of the dehiscence. Slow cine sweeps distinguish true tapering from artifact.
FIGURE 1.
(A) Transvaginal 2D gray scale ultrasound in the midsagittal plane of PAS Grade 3. Asterisk represents bulging placenta with multiple placenta lacunae. Arrowhead represents the caudal pole of the uterine dehiscence. (B) Same image from (A). The cervical canal is highlighted with a solid white line. The anterior lip of the cervix is seen transitioning to the residual wegde‐shaped portion of the myometrium in the lower uterine segment (dashed line), demonstrating the taper sign. (C) Transvaginal 2D gray scale ultrasound in the midsagittal plane demonstrating a placenta previa (P) without PAS in a patient with prior cesarean delivery. Here, the anterior lip of the cervix is seen extending into the lower uterine segment without any evidence of tapering (dashed line).
3.3. Clinical correlation
We have incorporated the taper sign into routine evaluation of patients with anterior placenta previa and prior cesarean delivery. The sign is easily obtained and highly reproducible in severe PAS cases.
In our experience, the taper sign corresponded to the region of maximal uterine disruption and deepest placental extension observed intraoperatively in Grade 3 PAS. The tapered myometrium is highly vascular on color Doppler, consistent with the neovascularization encountered intraoperatively along the lower uterine segment. These engorged myometrial and serosal vessels abut the thinnest area of dehiscence and carry the highest surgical bleeding risk. We have correlated this tapered area seen on antenatal imaging with intraoperative and histopathologic findings on post‐hysterectomy specimens (Figure 2).
FIGURE 2.
Gross pathology image of a hysterectomy specimen from a case of PAS Grade 3. The uterus and placenta are breadloafed and a section is shown of the lower uterine segment and cervix at the area of uterine dehiscence. The myometrium can be seen thinning at the cephalad and caudal poles of the dehiscence, creating a distinct wedge shape (dashed line) that correlates to the taper sign on antenatal ultrasound. The scar is seen as a thin layer of tissue bounding the placenta in the bulge.
In our practice, among 21 patients with anterior placenta previa, prior cesarean, and surgically and histopathologically confirmed PAS delivered from July 2024 to January 2026, the taper sign was observed in all 19 cases (100%) of FIGO Grade 3, and absent in both cases (100%) of FIGO Grade 1‐2, suggesting strong correlation with the uterine dehiscence specific to severe disease.
3.4. Impact on clinical management
The taper sign influenced management in several ways. First, it enhanced confidence in prenatal diagnosis of Grade 3 PAS, facilitating early multidisciplinary team involvement and delivery planning. Second, localizing the distal margin of dehiscence informed our surgical approach, particularly regarding hysterotomy planning and the anticipated area of maximal vascularity. Third, when other PAS markers were equivocal, the taper sign supported the decision for planned cesarean hysterectomy rather than attempted placental removal or resection with uterine conservation.
4. DISCUSSION
This report introduces the taper sign as a novel ultrasound marker associated with severe PAS and provides a standardized approach for its acquisition. For patients with anterior placenta previa and prior cesarean delivery, the taper sign has consistently identified severe PAS in our experience. Its reliance on grayscale imaging and simple anatomic landmarks enhances reproducibility across practice settings.
By depicting the uterine dehiscence in severe PAS, the taper sign aligns with contemporary pathophysiologic models of PAS and complements existing placental‐based markers. This marker can be verified intraoperatively and on post‐hysterectomy specimens as shown in this report.
Importantly, the taper sign is distinct from myometrial thinning. While myometrial thinning is a quantitative measurement, the taper sign provides complementary qualitative, morphologic information focusing on structural characteristics of the attenuated myometrium that uniquely correlates with PAS pathophysiology. Myometrial thinning (<1 mm) is a single‐point measurement, whereas the taper sign describes the progressive geometric configuration as the myometrium narrows from the cervix toward the point of complete dehiscence. The taper sign is best appreciated dynamically by tracing the anterior cervical lip into the lower uterine segment, providing anatomical context that single thickness measurements cannot capture. In our experience, the wedge‐shaped tapering pattern is specific for Grade 3 PAS, and it is not seen in low‐grade disease or cases of anterior previa without PAS (Figure 3A,B).
FIGURE 3.
Comparative ultrasound images demonstrating. (A) Anterior placenta previa with Grade 1 PAS in a patient with prior cesarean delivery. This figure demonstrates lacunae (asterisk), placental bulge, and general myometrial thinning (dashed line) suggestive of PAS, but without the characteristic wedge‐shaped tapering to a point that is seen with the dehiscence in Grade 3 PAS. (B) Anterior placenta previa without PAS in a patient with prior cesarean delivery. This figure demonstrates an otherwise normal‐appearing placenta with intact myometrium (dashed line).
Similarly, while placental bulge may reflect uterine attenuation with placental herniation, this finding focuses on placental appearance and can be present in low‐grade disease without dehiscence (Figure 3A).
The taper sign enhances recognition of severe disease, where prenatal diagnosis has major implications for risk stratification and surgical planning. It specifically localizes the distal margin of uterine dehiscence, corresponding to the area of maximal myometrial disruption and vascular engorgement. This complements PAS markers assessing lateral extension, bladder involvement, and depth of invasion [5]. This dynamic anatomical feature provides a visual roadmap to the specific location with the highest surgical risk.
Like other PAS markers, the taper sign should not be used in isolation. Placenta location, surgical history, and other patient characteristics and PAS markers must be considered. The taper sign completes the clinicopathologic story of PAS, adding uterine dehiscence to the ultrasound diagnosis. However, in the absence of other markers, tapering may represent simple dehiscence without deep placental implantation, a distinct entity requiring differentiation from severe PAS [8].
This report is limited by its descriptive design and lack of diagnostic performance assessment. Sensitivity, specificity, and predictive values cannot be inferred. Findings may not be generalizable to posterior placentation, low‐grade PAS, uterine anomalies, lower uterine segment fibroids, or patients without lower segment scars. Prospective studies with standardized protocols, blinded image review, and inter‐observer reliability assessment are needed to evaluate the diagnostic accuracy and performance in combination with established PAS markers.
5. CONCLUSION
The taper sign is a novel, easily reproducible ultrasound marker reflecting the progressive, wedge‐shaped myometrial narrowing at the distal margin of uterine dehiscence in severe PAS. This report provides a standardized description and imaging protocol intended to facilitate recognition of patients at increased risk for severe maternal morbidity. Further validation studies are warranted to define its diagnostic role within multimodal PAS assessment.
CONFLICT OF INTEREST STATEMENT
SAS received authorship honorarium from Oxford University Press and previously served on the Roche Pharmaceutical and Diagnostic Advisory Board.
Supporting information
Video 1: Transvaginal 2D gray scale ultrasound in the midsagittal plane of PAS Grade 3. Following the anterior lip of the cervix cephalad, the myometrium tapers to create a wedge‐shaped appearance resulting in the taper sign. The myometrium eventually disappears and is replaced by placental tissue at the area of complete dehiscence.
Video 2: Transvaginal split screen (left gray scale, right color Doppler) ultrasound in the midsagittal plane of PAS Grade 3. Hypervascularity is seen within the tapering myometrium of the anterior lower uterine segment highlighting the uterine vascular anatomy and neovascularization.
Supporting Information
Supporting Information
ACKNOWLEDGMENTS
Scott A. Shainker received salary and research support from Chase Koch Foundation and authorship royalties from Oxford University Press. He served on the Roche Pharmaceutical Diagnostic Advisory Board. Anna M. Modest received salary and research support from Chase Koch Foundation.
DATA AVAILABILITY STATEMENT
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Video 1: Transvaginal 2D gray scale ultrasound in the midsagittal plane of PAS Grade 3. Following the anterior lip of the cervix cephalad, the myometrium tapers to create a wedge‐shaped appearance resulting in the taper sign. The myometrium eventually disappears and is replaced by placental tissue at the area of complete dehiscence.
Video 2: Transvaginal split screen (left gray scale, right color Doppler) ultrasound in the midsagittal plane of PAS Grade 3. Hypervascularity is seen within the tapering myometrium of the anterior lower uterine segment highlighting the uterine vascular anatomy and neovascularization.
Supporting Information
Supporting Information
Data Availability Statement
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.