Role of modern ultrasonography in antenatal detection of placenta increta: a case report

Introduction / Введение

Placenta accreta is a severe pregnancy complication that occurs when placental tissue and blood vessels abnormally invade the uterine wall. The history of placenta accreta dates back more than a century. The earliest case documented in 1890 is reported from Tübingen, Germany, in 1890. Later, in 1937, C. Irving and A.T. Hertig published the first comprehensive case series, providing a systematic description and classification of abnormal placental adherence [1]. While earlier single case reports existed, their work laid the foundation for clinical recognition and standardization of the diagnosis.

In recent years, the terminology and classification of this pathology was revised. The term Placenta Accreta Spectrum (PAS) is now globally accepted and encompasses a range of abnormal placental adherence and invasion, including placenta accreta, increta, and percreta [2]. PAS disorders have become more prevalent alongside the global rise in cesarean deliveries, posing serious risks to both maternal and fetal health.

Etiological factors and risk stratification / Этиологические факторы и стратификация риска

PAS disorders are multifactorial in origin and are strongly associated with defective decidualization and excessive trophoblastic invasion. Normally, the decidua basalis provides a protective barrier that prevents chorionic villi from invading the myometrium. When this barrier lacks or underdeveloped, commonly due to previous uterine surgeries such as cesarean section, myomectomy, or curettage, the placenta may penetrate the myometrium pathologically [3].

Established risk factors for PAS include:

• multiple prior cesarean sections (with risk increasing with each subsequent operation);
• placenta previa, particularly overlying a uterine scar;
• advanced maternal age (≥ 35 years);
• uterine curettage or dilation and evacuation;
• assisted reproductive technologies (ART);
• uterine anomalies or intrauterine adhesions (e.g., Asherman’s syndrome).

These factors often overlap, increasing the overall risk. In the current case, the patient's history of multiple cesarean deliveries, placenta previa, and chronic urological conditions referred her to a high-risk category. Identifying such risk factors is essential for early diagnosis, appropriate imaging, and planning delivery in specialized centers.

The classification / Классификация

The traditional PAS classification used widely for many years is based on assessing the depth of chorionic villi invasion [4]:

• placenta accreta – superficial attachment of chorionic villi to the myometrium without penetration;
• placenta increta – deep invasion into the myometrium, disrupting its structure;
• placenta percreta – invasion through the entire myometrial thickness, potentially extending to the serosa, parametrium, peritoneum, or adjacent organs (e.g., bladder, intestines).

The currently accepted PAS classification was proposed by the International Federation of Gynecology and Obstetrics (FIGO), which includes [5]:

• PAS 1 – abnormally adherent placenta (creta);
• PAS 2 – abnormally invasive placenta (increta);
• PAS 3 – deeply invasive placenta (percreta).

The precise PAS etiopathogenesis remains under investigation. One hypothesis links PAS to defective decidual formation (e.g., lacked decidua basalis or underdeveloped fibrinoid layer), abnormal vascular remodeling during pregnancy, and excessive trophoblastic invasion, particularly following prior uterine surgery.

Placental adherence may be:

• complete – involving the entire area of implantation;
• partial – affecting localized zones.

Over the past four decades, cesarean section rates have risen by over 20 %, while PAS cases have increased tenfold [6]. The prevalence of PAS varies between 1 in 500 to 1 in 10,000 deliveries, with complete placental invasion being particularly rare – around 1 in 24,506 births [7][8]. Among PAS cases: accreta accounts for 60–75 %, increta for 15–20 %, and percreta for 5–10 %.

Diagnostic challenges and controversies / Проблемы диагностики и спорные вопросы

Despite ultrasound being the primary tool for PAS detection, distinguishing between placenta accreta, increta, and percreta remains challenging using grayscale imaging alone. Depth of invasion is difficult to assess due to overlapping sonographic features and variation in interpretation. Classic markers such as placental lacunae, myometrial thinning, and loss of the retroplacental clear zone are helpful but not specific, especially in early gestation.

Color Doppler imaging and emerging signs such as the “rail sign” (vascular bridging between placenta and adjacent tissues) improve diagnostic precision. However, these findings are not yet standardized and require operator experience and high-resolution equipment. Likewise, advanced tools like 3D power Doppler and shear-wave elastography are being explored but are not yet widely adopted into routine clinical protocols. Unlike most previously reported cases, current report highlights the diagnostic contribution of the "rail sign" on color Doppler as an early marker of placenta increta, verified later by MRI. To our knowledge, such a detailed correlation between Doppler vascular markers and intraoperative findings has been rarely documented.

The present case contributes to this field by demonstrating the practical value of vascular Doppler markers for diagnosing placenta increta and early signs of PAS 3a.

Developing diagnostics / Развитие диагностики

Historically, PAS was only diagnosed postnatally upon complicated placental separation or postpartum hemorrhage, as seen in early reports by Forster, Irving, and Hertig. Today, ultrasound is the primary modality for antenatal detection [9–12].

The meta-analysis by D’Antonio et al. assessing 3,070 high-risk pregnancies, demonstrated that ultrasound sensitivity and specificity comprised 90.72 % and 96.94 %, respectively, for PAS diagnosis [13].

Sonographic indicators of PAS include [14][15]:

• no clear hypoechoic zone between the placenta and myometrium;
• abnormal vascular lacunae with turbulent flow in the subplacental region;
• loss of the uterine-bladder interface;
• color Doppler is essential to confirm PAS and reduce false positives.

Key Doppler criteria include [10][11]:

• hypervascularization between the uterus and bladder;
• abnormal vascular branching beneath the placenta;
• low-resistance arterial and venous flow (> 15 cm/s) in the myometrium.

Early diagnosis allows for planned delivery in tertiary centers, reduces emergency hysterectomy rates, and improves maternal and neonatal outcomes. While cases of antenatal PAS diagnosis are well-documented globally, such reports are limited in Georgian literature. This article presents a clinical case that illustrates the role of modern ultrasound, particularly Doppler techniques, in the diagnosis and management of placenta increta.

Case presentation / Клинический случай

Patient D., 29 years old, has a history of three cesarean deliveries (in 2014, 2017, and 2025). The somatic history is significant for chronic pyelonephritis and urolithiasis.

The patient underwent routine screening examinations at 8, 12, 20, 23, and 28⁺⁶ weeks of gestation. Standard transvaginal and transabdominal ultrasounds were performed. After diagnosing placenta increta, magnetic resonance imaging (MRI) was additionally conducted. The diagnosis was confirmed intraoperatively and by histopathological examination.

At gestational age of 8 weeks, first-degree invasion of the gestational sac into the scar area was observed.

At 12–13 weeks of gestation, the placenta was localized on the anterior uterine wall, in the lower segment, covering the medial aspect of the postoperative scar and extending to the internal os of the endocervical canal – indicating placenta previa (Fig. 1).

During the 12-week screening, both placenta previa and partial invasion into the residual myometrium were identified. The patient was classified as high-risk for placental implantation anomalies and was informed about potential complications (Fig. 2).

At 19 weeks of gestation, the ultrasound revealed placenta previa localized over the anterior uterine wall at the site of the previous cesarean scar. The myometrial thickness over the scar was 3.2 mm, indicating its significant thinning. Multiple irregular placental lacunae, ranging in size from 4 to 10 mm, were observed with chaotic flow patterns (Fig. 3). Color Doppler examination showed hypervascularity in the retroplacental and bladder interface zone. Peak systolic velocities exceeded 20 cm/s, with low-resistance arterial and venous flow consistent with abnormally invasive vasculature (Fig. 4).

By 28⁺⁶ weeks of gestational age, placental bulging and invasion into the cervical canal were documented, consistent with PAS 3a. The Doppler “rail sign,” characterized by parallel bridging vessels extending from the myometrium through the serosa, was clearly visualized.

At 24 weeks of gestation, placenta previa was noted again. The myometrial structure could not be assessed as the placenta was fully invading it; the serosal layer remained intact, the endocervical canal was closed, with its length was 40 mm. According to the FIGO classification, this corresponded to PAS 2.

At 28⁺⁶ weeks of gestational age, transvaginal scanning revealed invasion of the placenta into the upper third of the cervix and the cervical canal corresponding to PAS 3a (Table 1).

Additional Doppler imaging allowed to identify vascular bridges (rail sign) extending from the myometrium through the serosal layer, defined as placenta increta (PAS 2).

Subsequent MRI confirmed complete placenta previa, with abnormal growth into the uterine scar and across all layers of the myometrium.

Doppler evaluation of blood flow proved to be a valuable tool for assessing the degree of abnormal placental invasion.

This clinical case demonstrates the effectiveness of modern ultrasonographic technologies, particularly color Doppler imaging, in diagnosing deep placental invasion. Although Jauniaux et al. previously emphasized the limitations for ultrasound in assessing the depth of placenta increta, this case challenges that viewpoint [16].

The MRI findings corroborated the Doppler-based suspicion of placenta increta with cervical extension (PAS 3a), confirming the depth of myometrial invasion and its relationship to adjacent structures [17]. The diagnostic features, such as myometrial thinning, enlarged lacunae, and abnormal vascular bridging (“rail sign”), are consistent with the FIGO classification for PAS and align with Jauniaux et al.’s standardized ultrasound descriptors. Furthermore, the approach is consistent with the Society for Maternal-Fetal Medicine (SMFM) recommendations, which emphasize the use of grayscale and Doppler imaging for antenatal diagnosis and risk stratification.

While the FIGO classification provides a standardized framework for defining PAS disorders, it has notable limitations. Several specialists have argued that its reliance on histopathological criteria offers little value intraoperatively, when real-time surgical decisions are required. Moreover, studies have highlighted that the FIGO grading does not correlate consistently with maternal morbidity, which limits its prognostic utility. In clinical practice, classifications based on surgical and imaging findings, such as those proposed by Jauniaux et al. (2019) or SMFM, may be more useful, as they emphasize parameters that directly influence management planning, surgical complexity, and outcomes [18]. Incorporating these clinically oriented frameworks alongside FIGO may therefore provide a more comprehensive approach for risk stratification and operative preparation.

We recognize that antenatal ultrasound PAS diagnosis has been well established in the literature. However, the presented case adds more value by demonstrating the utility of the "rail sign" in early gestation and confirming its correlation with MRI and histopathology, thereby reinforcing the clinical applicability of this marker in routine practice.

An additional limitation relates to the pathological assessment per se. Histopathological confirmation is traditionally regarded as the gold standard for PAS diagnosis; however, its validity has been questioned. The degree of placental adherence can vary even within the same specimen, and a diagnosis of placenta increta or percreta may be influenced by the site from which tissue is sampled. This introduces the risk of sampling bias and may lead to under- or over-classification of PAS severity. For this reason, intraoperative findings and the overall clinical context should be considered alongside histological results while establishing a definitive diagnosis.

Despite its high sensitivity and specificity, ultrasound (even when combined with color Doppler or MRI) cannot fully predict the intraoperative degree of surgical difficulty. Numerous studies have shown discrepancies between antenatal imaging findings and actual operative challenges, particularly regarding the extent of vascular invasion, adhesion severity, and risk of hemorrhage. Therefore, while imaging plays a critical role in early detection and management planning, it should not be overestimated as a predictor of surgical complexity. Multidisciplinary readiness and intraoperative adaptability remain essential in managing PAS cases.

Early detection of PAS, especially placenta percreta variants, is vital for maternal and fetal survival, allowing for planned surgical management in high-resource settings. This case illustrates how the integration of Doppler markers into standard prenatal surveillance can improve outcomes and reduce a need for emergency interventions. While limited to a single patient, the findings presented contribute to the growing body of evidence supporting the role for advanced ultrasound in PAS diagnosis. Further studies are needed to validate these vascular markers across diverse clinical settings.

Conclusion / Заключение

Over the past four decades, the rise in placenta accreta cases has underscored the urgent need for timely and accurate diagnosis of this high-risk pregnancy complication. The growing prevalence of PAS disorders parallels the global increase in cesarean deliveries. Current classification systems, such as the FIGO framework, have facilitated systematic diagnosis and clinical management of PAS variants.

This clinical case reinforces the value of ultrasound, including transvaginal scanning and Doppler imaging, as effective, accessible tools for evaluating the depth of placental invasion. Notably, the use of Doppler-based vascular signs, such as the “rail sign,” provided early indicators of placenta increta with cervical extension (PAS 3a), which were later verified by MRI. This case illustrates how the integration of advanced ultrasound technologies can markedly enhance diagnostic accuracy.

Early PAS identification allows for planned delivery in specialized centers, reducing maternal morbidity and emergency surgical interventions. The presented case underscores how incorporating Doppler markers into routine screening of high-risk patients can influence clinical decision-making, including the timing of delivery, surgical preparation, and maternal outcome optimization. Continuous ultrasonographic monitoring in high-risk pregnancies and incorporation of novel imaging markers into routine protocols may improve perinatal outcomes and guide future PAS management strategies.

While based on a single case, these findings highlight the promise of combining Doppler sonography with anatomical imaging, supporting future research into diagnostic standardization and validation.