{"paper_id":"0cceb225-eff2-4a98-97ea-7f8dec238418","body_text":"www.ogscience.org 1\nClinical insights into placenta accreta spectrum:  \na comprehensive review \nSul Lee, MD, PhD\n1,2\n, Seung-Chul Kim, MD, PhD\n1,2\nDepartment of Obstetrics and Gynecology, \n1\nBiomedical Research Institute, Pusan National University Hospital, \n2\nPusan National University School of \nMedicine, Busan, Korea\nPlacenta accreta spectrum (PAS) is defined by abnormal placental adherence or invasion into the myometrium \nor adjacent organs and is a leading cause of massive obstetric hemorrhage. Its global incidence is increasing due \nto rising cesarean delivery rates, uterine surgeries, and the use of assisted reproductive technologies. This review \nsummarizes the current knowledge regarding PAS, including its pathophysiology, risk factors, diagnostic methods, \ntreatment options, and pregnancy outcomes after conservative management. The underlying pathogenesis is related \nto defective decidualization at the endometrial-myometrial interface, which is commonly associated with uterine \nscarring. Prenatal diagnosis relies on a thorough clinical history and imaging tools such as ultrasound and magnetic \nresonance imaging. Management strategies depend on fertility preservation goals and range from hysterectomy to \nconservative approaches such as leaving the placenta in situ. Effective management requires early risk identification, \nprenatal screening, referral to specialized centers, and delivery planning by a multidisciplinary team. Despite recent \nadvances in imaging and surgical techniques, PAS remains the leading cause of maternal mortality and morbidity \nworldwide. There is a critical need for multicenter studies, standardized risk stratification tools, and long-term follow-\nup studies to optimize care and improve maternal and reproductive outcomes.\nKeywords: Placenta accreta spectrum; Postpartum hemorrhage; Physiopathology; Diagnosis; Disease management\nReview Article\nObstet Gynecol Sci 2026;69(1):1-15\nhttps://doi.org/10.5468/ogs.25231\neISSN 2287-8580\nIntroduction \nPlacenta accreta spectrum (PAS) refers to abnormal adher -\nence or invasion of the placenta into the myometrium, \npreventing normal separation after childbirth. It is a major \ncause of severe postpartum hemorrhage (PPH) and maternal \nmorbidity. Its global incidence has sharply increased in paral-\nlel with the rising rates of cesarean delivery, placenta previa, \nand other uterine surgeries [1,2]. Uterine scars, often result -\ning from cesarean delivery or myomectomy, are believed \nto create defects at the endometrial-myometrial interface. \nWhen placental implantation occurs in these areas, abnor -\nmal trophoblast infiltration and anchoring of villi adhesions \nmay contribute to PAS development. PAS, previously termed \nmorbidly adherent placenta or abnormally invasive placenta, \nencompasses a spectrum of conditions with varying degrees \nof villous invasion of the myometrium. Although the sensitiv-\nity and specificity of prenatal diagnosis have improved with \nthe use of ultrasound and magnetic resonance imaging (MRI) \nin high-risk pregnancies, it remains impossible to identify all \ncases antenatally, and unexpected massive hemorrhages at \ndelivery remain common. In response to these challenges, \nmajor professional societies such as the Society for Maternal-\nFetal Medicine (SMFM; 2021), the Royal College of Obstetri-\ncians and Gynecologists (RCOG; 2019), and the International \nFederation of Gynecology and Obstetrics (FIGO; 2018) have \nissued evidence-based guidelines to optimize diagnosis and \nArticles published in Obstet Gynecol Sci are open-access, distributed under the terms of \nthe Creative Commons Attribution Non-Commercial License (http://creativecommons.\norg/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, \nand reproduction in any medium, provided the original work is properly cited.\nCopyright © 2026 Korean Society of Obstetrics and Gynecology \nReceived: 2025.07.16.   Revised: 2025.09.28.   Accepted: 2025.10.09.\nCorresponding author: Seung-Chul Kim, MD, PhD\nDepartment of Obstetrics and Gynecology, Pusan National \nUniversity School of Medicine, 179 Gudeok-ro, Seo-gu, Busan \n49241, Korea\nE-mail: ksch0127@naver.com \nhttp//orcid.org/0000-0002-8174-9931\n\n\nwww.ogscience.org2\nVol. 69, No. 1, 2026\nmanagement. This review aims to synthesize the current \nknowledge by drawing upon these guidelines and recent \nliterature to provide a comprehensive overview of PAS diag -\nnosis and management.\nIncidence \nThe incidence of PAS is steadily increasing, which is largely \nattributed to an increase in the associated risk factors. In the \nU.S., the incidence dramatically increased from approximate-\nly 1 in 2,510 deliveries in 1970 to 1 in 272 deliveries in 2016 \n[3,4]. A population-based study published in 2021 reported \na PAS incidence rate of 0.48% between 2013 and 2015 [5]. \nThis upward trend in incidence appears to be influenced by \ndemographic shifts such as advanced maternal age and the \nincreased use of assisted reproductive technology (ART). Fur-\nthermore, improvements in the sensitivity of diagnostic tools \nhave played a significant role [6]. Notably, advancements in \nimaging techniques since 2010, including high-resolution ul-\ntrasonography and MRI, have enhanced the prenatal detec -\ntion rate of PAS. Consequently, this has led to an increase in \nthe reported incidence, as milder cases that might have gone \nundiagnosed previously are now being identified. Interesting-\nly, some studies have observed regional or ethnic variations \nwith relatively low incidence rates reported in certain Asian \ncountries [7,8]. \nAlthough somewhat dated, the most reliable domestic \ndata on PAS in Korea were obtained from a retrospective \npathology-based study conducted between 1995 and 1999. \nThis study reported a PAS incidence of approximately 0.267% \namong all deliveries. Of these, placenta accreta accounts for \n35%, placenta increta for 60%, and placenta percreta for 5% \n[9]. Although recent nationwide data on the PAS incidence \nin Korea are lacking, a Japanese nationwide prospective birth \ncohort study published in 2019 reported an incidence rate \nof approximately 0.6% [7]. Given the high prevalence of \nadvanced maternal age and persistently high cesarean deliv -\nery rates in Korea, the actual incidence of PAS in the Korean \npopulation may exceed that observed in Japan.\nPathogenesis\nThe pathophysiology of PAS is primarily attributed to defec -\ntive decidua rather than to inherently invasive trophoblasts. \nIn normal pregnancy, extravillous trophoblast infiltration is ar-\nrested at the decidual spongiosus; however, surgical disrup -\ntion, such as a prior cesarean scar, compromises the endome-\ntrial-myometrial interface, eliminating the inhibitory signals \nthat normally restrain trophoblast invasion [10,11]. Recent \nreviews have indicated that dysregulation of angiogenic sig -\nnaling, integrin expression, and hypoxia-inducible pathways \nexacerbates abnormal trophoblast invasion in PAS [12]. Other \nproposed mechanisms contributing to PAS include altered \ninflammatory response at the implantation site and abnor -\nmal angiogenesis. Some studies have suggested that an \nexaggerated or chronic inflammatory state in the uterine scar \nmay promote the invasive properties of trophoblasts. Addi -\ntionally, dysregulation of the expression of various adhesion \nmolecules, growth factors, and cytokines at the maternal-\nfetal interface can facilitate abnormal placental attachment \nand invasion [13,14]. Emerging evidence also highlights the \nabnormal expression of integrins, excessive activity of matrix \nmetalloproteinases, and hypoxia-related signaling pathways, \nall of which may enhance defective decidualization and ex -\ncessive trophoblast infiltration. Abnormal remodeling of the \nspiral arteries and altered vascular architecture within the \nscar tissue may also contribute to the unique pathological \nfeatures observed in PAS. Abnormal uterine healing after \na cesarean delivery may contribute to the development of \nPAS. Previous studies have suggested that single- or double-\nlayer continuous uterine sutures may shorten the operative \ntime and reduce blood loss by facilitating rapid closure of \nthe incision site. However, excessive pressure on the myo -\nmetrium and the ischemic effects of continuous suturing \nmay impair optimal wound healing, although supporting \nevidence remains limited. Inadequate scar healing can reduce \nthe protective barrier against trophoblast invasion, predis -\nposing patients to PAS. A case-control study reported that \ncontinuous inner-layer uterine sutures were associated with a \nsignificantly increased risk of PAS compared with interrupted \nsutures, possibly due to localized ischemia and scar forma -\ntion. The adjusted odds ratio (OR) for PAS in patients with \ncontinuous sutures was 6.0 (95% confidence interval [CI], \n1.4-25.2; P=0.015). These findings support the hypothesis \nthat excessive tightening or non-physiological closure may \nimpair endometrial regeneration and predispose patients to \nabnormal placental attachment [15]. These combined factors \nlead to the failure of physiological decidual separation dur -\n\nwww.ogscience.org 3\nSul Lee, et al. PAS: clinical insights\ning the third stage of labor, resulting in massive hemorrhage \nupon attempted manual removal of the placenta.\nRisk factor\nThe most well-established pathophysiological mechanism of \nPAS is the failure of normal decidualization due to a defect \nin the endometrial-myometrial interface. This defect is often \ncaused by uterine scarring from previous surgeries such as \ncesarean delivery, myomectomy, adenomyomectomy, or dila-\ntion and curettage. These procedures are recognized as risk \nfactors of PAS.\n1. Cesarean delivery\nThe global increase in cesarean delivery rates is strongly as -\nsociated with the rising incidence of PAS, a fact well-docu -\nmented in numerous studies [16,17]. A matched case-control \nstudy conducted in the U.S. in 2005 reported that the inci -\ndence of PAS after cesarean delivery increased from 12.5% \nin 1982 to 23.5% in 2002 [3]. Similarly, a cohort study from \nHong Kong in 2015 observed an increase in PAS disorder \nfrom 0.17 per 1,000 deliveries in 1999-2003 to 0.79 per \n1,000 deliveries in 2009-2013 [18]. A recent meta-analysis \nreported a summary OR of 1.96 (95% CI, 1.41-2.74) for PAS \nfollowing a single cesarean delivery [19]. \nThe risk of PAS increased significantly with the number of \nprevious cesarean deliveries. A large prospective cohort study \nconducted in the U.S. in 2014 found that patients with two \nor three prior cesarean deliveries had an adjusted OR for ac -\ncreta of 7.7 (95% CI, 2.4-24.9) [20]. Furthermore, a large \npopulation-based pregnancy cohort study published in 2016 \nreported ORs for PAS of 8.6 (95% CI, 3.5-21.1) for one prior \ncesarean, 17.4 (95% CI, 9.0-31.4) for two, and a substan -\ntial increase to 55.9 (95% CI, 25.0-110.3) for three or more \nprior cesarean deliveries [21]. Beyond the number of previous \ncesarean sections, a classical hysterotomy incision has also \nbeen reported to increase the risk of PAS compared to a low-\nsegment hysterotomy incision [22].\nWhen cesarean scar pregnancy (CSP) occurs as a result of \nprior cesarean delivery, the risk of subsequent PAS increases \nsubstantially. CSP is considered a significant precursor of \nPAS. CSP occurs when a gestational sac implants within \nthe fibrous scar of a previous cesarean section, impairing \nnormal decidualization. This abnormal implantation and \ndefective decidual layer facilitate direct placental invasion of \nthe myometrium [23]. Histologically, CSP and PAS share a \nsimilar spectrum of defective decidualization and abnormal \ntrophoblastic invasion at scar sites. Accordingly, CSP has \nbeen classified into two main types: endogenic (type 1), in \nwhich the gestational sac grows toward the uterine cavity, \nand exogenic (type 2), in which the sac deeply invades the \nmyometrium or bladder wall; the latter is strongly associated \nwith progression to PAS [24]. More recently, an updated clas-\nsification has been proposed, refining the diagnostic criteria \nand emphasizing its role as an early stage of PAS [25].\n2. Myomectomy and adenomyomectomy\nAlthough clear evidence directly linking myoma or adeno -\nmyosis to invasive placentation is limited, major uterine sur -\ngeries such as myomectomy and adenomyomectomy share \na pathophysiological mechanism similar to that of cesarean \ndelivery in predisposing patients to PAS. A nationwide cohort \nstudy investigating the incidence of PAS after myomectomy \nreported an incidence of 0.96% in women with a history of \nmyomectomy compared to 0.20% in those without, yielding \nan adjusted OR of 2.28 (95% CI, 1.85-2.81) [26]. Although \nlarge-scale studies specifically on the incidence of PAS after \nadenomyomectomy are currently lacking, some smaller re -\nports have indicated a trend towards increased PAS incidence \nfollowing this procedure [27].\n3. Placenta previa\nPlacenta previa is another critical risk factor for PAS. It is es -\ntimated to occur in approximately 1 in 200-300 births and \nnotably, approximately 11% of women with placenta previa \nalso have concomitant PAS [28]. A recent systematic review \nand meta-analysis found that PAS without previa is generally \nless severe, with a lower risk of invasive placenta (OR, 0.24), \nreduced blood loss (mean difference, 1.19 L), and fewer hys-\nterectomies (OR, 0.11) [29]. The incidence of placenta previa \nincreases with a history of previous cesarean deliveries and \nthe risk further escalates with subsequent cesarean delivery \n[30]. Consequently, the combination of a history of cesarean  \ndelivery and placenta previa dramatically increases the in -\ncidence of PAS. While PAS occurs in approximately 4% of \ncases with placenta previa but no prior cesarean deliveries, its \nincidence surges to between 50% and 67% when placenta \nprevia is combined with three or more previous cesarean de-\nliveries [31]. \n\nwww.ogscience.org4\nVol. 69, No. 1, 2026\n4. Other risk factors\nSeveral other conditions and procedures have also been re -\nported as risk factors for placenta accreta, including uterine \nanomalies, endometritis, ART, uterine artery embolization \n(UAE), chemotherapy, and radiation [20,32-34]. Uterine cu -\nrettage, endometrial ablation, and hysteroscopic surgery can \ncause myometrial defects and scarring, thereby increasing \nthe risk of developing PAS in future pregnancies [35,36]. ART \nis also a potential contributor to PAS. The mechanisms may \ninvolve poor decidualization due to suboptimal preparation, \na thin endometrium, or repeated injury [37,38]. Addition -\nally, abnormal implantation in the lower uterine segment or \ncesarean scar sites during embryo transfer may predispose \nto PAS [39]. ART pregnancies often involve multiple uterine \nanomalies, which may increase the risk of PAS. A 2012 UK \nObstetric Surveillance System study reported an adjusted OR \nof approximately 32.1 (95% CI, 2.0-509) for PAS disorders \nin in-vitro fertilization pregnancies [40]. However, a recent \nmeta-analysis of cohort studies reported no significant dif -\nference in the relative risk between ART and spontaneous \nsingleton pregnancies [41], suggesting that further research \nis warranted to clarify this association. According to a retro -\nspective cross-sectional study of 2,223 women with histo -\nlogically verified PAS disorders, prior endometritis was inde -\npendently associated with a three-fold increased risk of PPH \n(OR, 3.01; 95% CI, 1.06-9.02). This suggests that infection-\nrelated damage may worsen placentation and bleeding risk \nin patients with PAS. Although this study primarily investigat-\ned PPH, the observed link supports the role of endometrial \ninflammation in the pathophysiology of PAS [42].\nClassification\nWhile the definitive diagnosis of PAS is ultimately established \nby histopathology, clinical practice often involves prenatal \nor intraoperative diagnoses due to efforts to preserve the \nuterus through various surgical techniques and conservative \nmanagement, such as UAE, before resorting to cesarean \nhysterectomy. Consequently, the number of cases diagnosed \nprenatally or intraoperatively significantly outweighed the \nnumber of cases confirmed histopathologically.\nThe FIGO recently introduced a comprehensive grading sys-\ntem for diagnosing PAS (Table 1). \nThis system classifies PAS into three distinct grades (grade 1 \nto grade 3), each defined according to specific clinical and \nhistological criteria. Grade 1 represents cases in which the \nplacenta adheres to the myometrium and the adherence is \nabnormal. Grade 2 signified invasion of the myometrium. \nGrade 3, specifically designated as percreta, indicates full-\nthickness invasion through the myometrium, potentially in -\nvolving the adjacent organs. Grade 3 is further subclassified \ninto 3a, 3b, and 3c based on the extent and type of involve-\nment of the surrounding structures, such as the serosa, blad-\nder, or other pelvic organs. This standardized grading system \naims to improve the consistency of diagnoses and guide \nmanagement strategies.\nPrenatal screening and diagnosis  \nThe only way to definitively diagnose PAS is through histo -\npathology, which can occur after the surgical removal of the \nuterus. In cases where there is an attempt to save the uterus \nbut only part of the placenta shows abnormal adherence, \na definitive histopathological diagnosis is often not possible \nand will instead remain clinically suspicious. Given the high \nrisk of massive hemorrhage and maternal morbidity associ -\nated with PAS, antenatal identification and delivery planning \nin a specialized facility are necessary. This also emphasizes \nthe importance of early prenatal diagnosis and the ability \nto stratify risks, especially during the first trimester. First-\ntrimester ultrasonography is especially valuable in difficult \ncases early in pregnancy, such as the posterior placenta or \npercreta, as later imaging may underestimate the depth of \ninvasion because of acoustic shadowing or limited visualiza -\ntion. Early detection under these circumstances increases \nthe potential for accurate diagnosis and multidisciplinary \npreparation. Throughout pregnancy, ultrasound and MRI \nremain the primary imaging modalities used. While maternal \nserum markers like β-human chorionic gonadotropin (β-hCG), \npregnancy-associated plasma protein A (PAPP-A), and alpha-\nfetoprotein (AFP) have been associated with PAS in some \nstudies, their effectiveness as diagnostic tests is limited, and \nthey are not recommended as standalone tools for screening. \nNew biomarkers are being studied and require further clinical \ntesting before being considered for practical use.\n\nwww.ogscience.org 5\nSul Lee, et al. PAS: clinical insights\nTable 1. General classification of PAS from the FIGO grading system [79]\nGrade 1: abnormally adherent placenta (placenta adherent or creta)\nClinical criteria\nAt vaginal delivery\nNo separation with synthetic oxytocin and gentle controlled cord traction\nAttempts at manual removal of the placenta results in heavy bleeding from the placental implantation site requiring mechanical or \nsurgical procedure\nIf laparotomy is required (including for cesarean delivery)\nSame as above\nMacroscopically, the uterus show no obvious distension over the placental bed (placental “bulge”), no placental tissue is seen invading \nthrough the surface of the uterus, and there is no or minimal neovascularity\nHistologic criteria\nMicroscopic examination of the placental bed samples from hysterectomy specimen shows extended areas of absent decidua between \nvillous tissue and myometrium with placental villi attached directly to the superficial myometrium\nThe diagnosis cannot be made on just delivered placental tissue nor on random biopsies of the placental bed\nGrade 2: abnormally invasive placenta (increta)\nClinical criteria\nAt laparotomy\nAbnormal macroscopic findings over the placental bed: bluish/purple coloring, distension (placental “bulge”)\nSignificant amounts of hypervascularity (dense tangled bed of vessels or multiple vessels running parallel craniocaudially in the uterine \nserosa)\nNo placental tissue seen to be invading through the uterine serosa\nGentle cord traction results in the uterus being pulled inwards without separation of the placenta (so-called the dimple sign)\nHistologic criteria\nHysterectomy specimen or partial myometrial resection of the increta area shows placental villi within the muscular fibers and sometimes \nin the lumen of the deep uterine vasculature (radial or arcuate arteries)\nGrade 3: abnormally invasive placenta (percreta)\nGrade 3a: limited to the uterine serosa\nClinical criteria\nAt laparotomy\nAbnormal macroscopic findings on uterine serosal surface (as above) and placental tissue seen to be invading through the surface of the \nuterus\nNo invasion into any other organ, including the posterior wall of the bladder (a clear surgical plane can be identified between the \nbladder and uterus)\nHistologic criteria\nHysterectomy specimen showing villous tissue within or breaching the uterine serosa\nGrade 3b: with urinary bladder invasion\nClinical criteria\nAt laparotomy\nPlacenta villi are seen to be invading into the bladder but no other organs\nClear surgical plane cannot be identified between the bladder and uterus\nHistologic criteria\nHysterectomy specimen showing villous tissue breaching the uterine serosa and the bladder wall tissue or urothelium\nGrade 3c: with invasion of other pelvic tissue/organs\nClinical criteria\nAt laparotomy\nPlacenta villi are seen to be invading into the broad ligament, vaginal wall, pelvic sidewall or any other pelvic organ (with or without \ninvasion of the bladder)\nClear surgical plane cannot be identified between the bladder and uterus\nHistologic criteria\nHysterectomy specimen showing villous tissue breaching the uterine serosa and invading pelvic tissues/organs (with or without invasion \nof the bladder)\nPAS, placenta accreta spectrum; FIGO, International Federation of Gynecology and Obstetrics.\n\nwww.ogscience.org6\nVol. 69, No. 1, 2026\n1. Obstetric sonography\nObstetric ultrasound is the primary and most essential tool \nfor the prenatal diagnosis of PAS. However, diagnostic ac -\ncuracy can be influenced by the examiner’s skill, gestational \nage, and equipment performance. While simple grayscale \nimaging alone has reported sensitivities ranging from ap -\nproximately 50% to 87%, the addition of color Doppler \nimaging significantly improves the diagnostic accuracy. A re-\ncent systematic review and meta-analysis demonstrated that, \nwhen performed by highly experienced operators, ultrasound \nachieved a sensitivity of 90.72%, a specificity of 96.94%, \nand a diagnostic OR of 98.59 for PAS diagnosis [43]. Three-\ndimensional ultrasonography can also be used as an adjunct \ntool. The antenatal diagnosis of PAS was significantly higher \nin women with coexisting placenta previa (72.3%) than in \nthose without (6.9%), highlighting the challenge of diagnos-\ning PAS in the absence of previa (P<0.001) [44]. Therefore, \nPAS diagnosis cannot rely solely on ultrasound, as it has \ninherent limitations, particularly in the absence of placenta \nprevia. The use of additional diagnostic tools is necessary to \nimprove the detection accuracy. Sonographic features associ-\nated with placenta accreta have recently been systematically \ncategorized by the International Society for PAS (Table 2).\nThe “loss of clear zone” finding, while relatively easy to \ndetect, has a notable drawback of a somewhat high false-\npositive rate of approximately 21% [45]. In contrast, ab -\nnormal placental lacunae, also known as the “Swiss cheese \nappearance” due to the vascular spaces within the placental \nparenchyma, boast a high sensitivity of 80-90% and a low \nfalse-positive rate. This makes it one of the most critical ultra-\nTable 2. IS-PAS unified descriptors for PAS disorders\nUS finding IS-PAS suggested standardized definition\n2D grayscale \nLoss of ‘clear zone’ Loss, or irregularity, of hypoechoic plane in myometrium underneath placental bed (‘clear zone’)\nAbnormal placenta lacunae Presence of numerous lacunae including some that are large and irregular (finberg grade 3), often \ncontaining turbulent flow visible on grayscale imaging\nBladder wall interruption Loss or interruption of bright bladder wall (hyperechoic band or ‘line’ between uterine serosa and \nbladder lumen)\nMyometrial thinning Thinning of myometrium overlying placenta to <1 mm or undetectable\nPlacental bulge Deviation of uterine serosa away from expected plane, caused by abnormal bulge of placental \ntissue into neighboring organ, typically bladder; uterine serosa appears intact but outline shape is \ndistorted\nFocal exophytic mass Placenta tissue seen breaking through uterine serosa and extending beyond it; most often seen \ninside filled urinary bladder\n2D color Doppler\nUterovesical hypervascularity Striking amount of color Doppler signal seen between myometrium and posterior wall of \nbladder; this sign probably indicates numerous, closely packed, tortuous vessels in that region \n(demonstrating multidirectional flow and aliasing artifact)\nSubplacental hypervascularity Striking amount of color doppler signal seen in placental bed; this sign probably indicates numerous, \nclosely packed, tortuous vessels in that region (demonstrating multidirectional flow and aliasing \nartifact)\nBridging vessels Vessels appearing to extend from placenta, across myometrium and beyond serosa into bladder or \nother organs; often running perpendicular to myometrium\nPlacenta lacunae feeder vessels Vessels with high-velocity blood flow leading from myometrium into placental lacunae, causing \nturbulence upon entry\n3D ultrasound±power Doppler\nIntraplacental hypervascularity Complex, irregular arrangement of numerous placental vessels, exhibiting tortuous courses and \nvarying calibers\nModified from Collins et al. [80].\nIS-PAS, International Society for placenta accreta spectrum; PAS, placenta accreta spectrum; US, ultrosound; 2D, two-dimensional; 3D, three-\ndimensional.\n\nwww.ogscience.org 7\nSul Lee, et al. PAS: clinical insights\nsound findings in the diagnosis of PAS. Identifying the turbu-\nlent blood flow within these lacunae using color Doppler also \naids in predicting PAS. Furthermore, observing bladder wall \ninterruption along with increased vascularity at the uterovesi-\ncal interface using color Doppler provides highly sensitive \nand specific indicators of PAS [46]. Myometrial thinning, with \napproximately 93% sensitivity and 79% specificity, is another \nkey sign of PAS and is often observed in conjunction with \nlacunae. For an accurate assessment of bladder wall interrup-\ntion, placental bulging, and uterovesical hypervascularity, it \nis crucial to examine the bladder filled to 200-300 mL. Com-\nbining these various ultrasound findings allows the predic -\ntion of the PAS grade and extent of accreta placentation. Ac-\ncording to a recent meta-analysis, ultrasound demonstrated \na pooled sensitivity of approximately 90% and specificity of \n97% for PAS diagnosis, with the highest accuracy when per-\nformed by experienced operators [47]. The current FIGO and \nAmerican College of Obstetricians and Gynecologists (ACOG) \nguidelines recommend ultrasound as the first-line diagnostic \nmodality, reserving MRI scans for equivocal or complex cases. \nAlthough ultrasonography remains the cornerstone of PAS \ndiagnosis, several antenatal scoring systems have been devel-\noped that integrate sonographic features (such as placental \nlacunae, myometrial thinning, and loss of the clear zone) \nwith clinical risk factors to improve predictive accuracy. These \nmodels, such as the placenta accreta index (PAI), can support \nearly recognition of high-risk patients, although their broader \nclinical utility lies in referral and management planning.\n2. MRI \nMRI is highly valuable for diagnosing PAS, offering sensitiv -\nity and specificity comparable to those of ultrasonography. \nIt is particularly effective when the placenta is located pos -\nteriorly, which makes ultrasound assessment challenging. \nFurthermore, MRI provides superior evaluation of myometrial \ninvolvement, bladder invasion, and depth of placental inva -\nsion compared to ultrasound. The optimal timing for MRI is \ngenerally between 24 weeks and 30 weeks of gestation [48]. \nIntravenous contrast agents are typically not administered \nduring prenatal MRI due to concerns regarding fetal toxicity. \nMRI findings of PAS include both direct signs, which indicate \nabnormal placental invasion, and indirect signs, which indi -\ncate secondary effects on the placental parenchyma or vas -\nculature [49]. \nCompared with ultrasound, MRI demonstrates a pooled \nsensitivity of 83% and a specificity of 84%; however, in -\nterobserver variability remains higher, and diagnostic ac -\ncuracy is more dependent on expertise [47,50]. MRI is most \nuseful when ultrasound findings are inconclusive, particularly \nfor posterior placentation, maternal obesity, or when para -\nmetrial or bladder invasion is suspected. Thus, the guidelines \nemphasize MRI as a complementary problem-solving tool, \nrather than as a routine screening modality.\nOn MRI, indirect indicators of PAS include placental het -\nerogeneity, T2 dark bands, and abnormal hypervascularity \ncharacterized by tortuous, ectatic intraparenchymal vessels \nand proliferated retroplacental or pelvic veins. Direct signs \ncomprise focal defects in the myometrial wall and bladder \ntenting, while unequivocal invasion into adjacent organs is \nhighly suggestive of placenta percreta [49].\nPlacental bulging is identified as a deviation of the uterine \nserosa away from its expected plane. This sign is considered \nthe most useful when observed in isolation. It can appear \neither focally or diffusely, with diffuse bulging potentially \naltering the normal inverted-pear shape of the uterus [51].  \nPlacental heterogeneity is a subjective concept and its degree \nis determined by an interpreting radiologist. As an indirect \nsign of PAS, it involves an overall assessment of the placental \ncondition. It manifests as a mixture of abnormal intraplacen-\ntal hypervascularity, irregular or undulating contours, and T2 \ndark bands. T2 dark bands appear as bands traversing the \nperpendicular axis of the placenta, often originating from \nthe maternal surface and extending towards the fetal surface \nwith variable thickness. These bands were thought to repre -\nsent fibrin deposition. Intraplacental hypervascularity requires \ncareful differentiation from normal placental vascularity. \nAbnormally hypervascular areas typically exhibit enlarged \nintraparenchymal vessels that appear bizarre, disorganized, \nor ectatic. The absence of the typical uterine trilaminar layer \n(hypo-hyper-hypointense signal) due to focal interruptions \nin the myometrial wall suggests PAS. However, identifying \nmyometrial line disruption along the entire uterine wall can \nbe challenging, leading to an increased risk of false positives. \nBladder stenting, defined as the elongation of the bladder \ndome towards the uterine wall, is another important sign. \nThe thinning and irregularity of the normally hypointense \nbladder wall suggested bladder invasion. The presence of ex-\ntrauterine invasion, such as invasion into the bladder or ad -\njacent structures or a focal exophytic mass, strongly suggests \nplacenta percreta.\n\nwww.ogscience.org8\nVol. 69, No. 1, 2026\n3. Prenatal biomarker for PAS\nAt 11-12 weeks of gestation, lower levels of β-hCG and \nhigher levels of PAPP-A have been associated with an in -\ncreased risk of PAS. In the second trimester, maternal serum \nAFP and β-hCG levels exceeding 2.5 multiples of the median \ncompared to normal pregnancies have also shown a signifi -\ncant association with PAS [34,52]. In contrast, cell-free fetal \nDNA testing did not demonstrate significant differences be -\ntween pregnancies affected by PAS and those with normal \nplacentation [53]. Due to the limited diagnostic accuracy of \nthese serum markers, they are not recommended as stand -\nalone clinical screening tools for PAS.\n4. Emerging trends in PAS diagnosis\nRecent advances are beginning to reshape the diagnostic \nparadigm for PAS. Machine learning and radiomics models \nthat automatically analyze imaging features have shown \npromise. In a recent pilot study, machine learning algorithms \napplied to ultrasound images achieved promising discrimina-\ntion between patients with PAS and healthy controls [54]. \nAnother model combining MRI radiomics and clinical signa -\ntures reported an accuracy of up to 0.825, a sensitivity of \n0.830, and a specificity of 0.822 in an external validation \ncohort for PAS detection [55]. Simultaneously, molecular bio-\nmarkers are currently being investigated. A systematic review \nof new molecular biomarkers (transcriptomics, genomics, and \nprotein-based markers) highlighted several candidate mark -\ners (e.g., miRNAs and growth factors) that may distinguish \nabnormal placentation from normal pregnancies, although \nmost remain experimental [56]. Although these approaches \nare not yet a part of standard care, predictive models that \nintegrate imaging, clinical data, and molecular markers have \nthe potential to improve risk stratification and individualized \ndiagnosis. Continued research and prospective validation are \nessential before widespread clinical adoption.\nManagement \nThe management of PAS is broadly categorized as antepar -\ntum, intrapartum, and postpartum. Furthermore, it can be \nclassified as either conservative (aimed at fertility preserva -\ntion) or nonconservative (surgical) management, depending \non the goal of preserving future fertility. The ideal therapeu-\ntic strategy for patients with PAS involves planned delivery at \na tertiary care hospital, with the active involvement of a mul-\ntidisciplinary care team comprising specialists from obstetrics, \nanesthesiology, urology, and critical care. When properly \nimplemented, this comprehensive approach can significantly \nimprove maternal outcomes, even in severe cases of PAS.\n1. Antepartum management\n1) Patient selection\nAlthough PAS can sometimes be an unexpected intrapartum \ndiagnosis, the most critical step before delivery is to identify \nindividuals at risk for PAS. History taking to uncover relevant \nrisk factors plays a crucial role in the screening of these pa -\ntients. Confirming the history and number of previous cesar-\nean deliveries, other major or minor uterine surgeries, or cur-\nrent pregnancy status via ART facilitates the identification of \nsonographic signs suggestive of PAS. Once appropriate can -\ndidates are identified based on their history, further screening \ninvolves the identification of PAS-specific signs via ultrasound \nor MRI to select those with a strong suspicion of PAS. At this \nstage, maternal biomarkers such as AFP and β-hCG can also \nbe checked. \n2) Risk stratification and scoring systems\nAccurate antenatal risk stratification is an important com -\nponent of PAS management. In addition to recognizing \ntraditional risk factors, structured scoring systems have been \nproposed to improve predictions and guide referrals. One \nsuch model is the PAI, which integrates clinical history (e.g., \nnumber of prior cesarean deliveries and placental location) \nwith ultrasound findings such as placental lacunae, loss of \nthe clear zone, and myometrial thickness. Validation studies \nhave demonstrated that higher PAI scores are associated with \nan increased probability of PAS and greater disease severity \n[57]. Recently, other ultrasound-based scoring systems have \nbeen proposed. For example, Zhang et al. [58] developed a \nmultiparameter scoring system incorporating placental la -\ncunae, myometrial thinning, bladder wall interruption, and \nbridging vessels, reporting an area under the curve of 0.93 \nfor PAS prediction. Similarly, Pekar Zlotin et al. [59] evaluated \na clinical-sonographic score combining patient risk factors \nwith imaging features and demonstrated improved accuracy \nin stratifying patients at high risk of PAS. Although none of \nthese tools have been universally adopted, they are increas -\ningly being utilized in tertiary centers to aid early referral to \n\nwww.ogscience.org 9\nSul Lee, et al. PAS: clinical insights\nspecialized PAS care units and to support multidisciplinary \ndelivery planning. Future studies are required to validate their \nperformance across diverse populations and standardize their \napplication in clinical practice. \n3) Transfer to a center of excellence\nOnce a high-risk patient is identified, delivery transfer should \nbe considered. The transfer should be to a facility equipped \nwith a multidisciplinary team. Optimal management of PAS \nrelies on a coordinated multidisciplinary team. Anesthesi -\nologists ensure perioperative hemodynamic stability and \nrequire massive transfusion. Urology assists with bladder or \nureteral involvement, including stenting or surgical repair. \nInterventional radiology may provide adjunctive control of \nthe hemorrhage through balloon occlusion or embolization \nin selected cases. Blood bank coordination is essential for the \ntimely preparation and rapid availability of blood products. \nEarly referral to specialized centers, where such expertise is \navailable, is crucial for improving maternal outcomes. Addi -\ntionally, the center should have 24-hour access to a surgical \nor medical intensive care unit and a neonatal intensive care \nunit, along with the capacity for rapid blood transfusion to \nmanage massive hemorrhage [60]. \n4) Time of delivery\nFor women with suspected PAS, the delivery method is \nplanned cesarean delivery. The optimal timing for such \nplanned deliveries must carefully balance maternal risks with \nneonatal benefits. One study reported that approximately \n40% of women diagnosed with PAS experienced unplanned \ndeliveries due to bleeding before 34 weeks of gestation [61].  \nTherefore, the ACOG recommends delivery between 34 weeks \nand 0 days and 35 weeks and 6 days [32]. Similarly, the SMFM \nrecommends that in asymptomatic patients with confirmed \nPAS, a planned cesarean hysterectomy should be scheduled \nbetween 34+0 weeks and 35+6 weeks of gestation [62]. If \nvaginal bleeding commences earlier, antenatal corticosteroid \nadministration should be considered depending on the clini-\ncal situation. The RCOG suggests planned delivery at 36+0-\n37+0 weeks in stable patients, while early delivery between \n34+0 and 36+6 weeks should be considered in cases with \nan increased risk of bleeding or spontaneous labor [63]. The \nFIGO acknowledges delivery between 34+0 weeks and 36+6 \nweeks as reasonable for most PAS cases and recommends \nearlier intervention in the presence of maternal or fetal com-\nplications [47]. \n2. Intrapartum and postpartum management\nTable 3 outlines the recommended management strategies \nfor PAS according to the FIGO staging. \n1) Nonconservative surgical management\nCesarean hysterectomy is often the primary treatment for \nprenatally diagnosed PAS. In regions where additional con -\nservative management is not readily available, cesarean \nhysterectomy is the most appropriate treatment option. This \nmethod involves delivering the fetus while leaving the pla -\ncenta in situ within the uterus, which helps reduce immedi -\nate massive hemorrhage from attempted placental removal. \nApproximately 80-90% of PAS diagnoses lead to either \nemergent or elective cesarean hysterectomy [64]. Hysterecto-\nmy is particularly common when placenta increta or percreta \nis suspected. \nSignificant blood loss, typically ranging from 2-3 L, is antici-\nTable 3. Suggested management strategies according to FIGO grading of PAS\nFIGO grade Suggested management\nGrade 1 (accreta/creta) Conservative or uterus-preserving approaches may be considered in selected cases (e.g., local \nresection, repair)\nGrade 2 (increta) Cesarean hysterectomy is the preferred treatment when invasion is deeper; conservative \nmanagement may only be attempted in highly selected settings\nGrade 3a (percreta limited to serosa) In most cases, the placenta should not be removed and cesarean hysterectomy should be planned\nGrade 3b (percreta with bladder \ninvasion)\nHysterectomy with partial cystectomy or urologic reconstruction should be anticipated when \ninvasion of the bladder is present (implied in FIGO invasive percreta management)\nGrade 3c (percreta with extension to \nother pelvic organs)\nMultidisciplinary surgery with possible exenterative approach is required in extensive organ invasion \n(supported by FIGO statements on advanced percreta)\nFIGO, International Federation of Gynecology and Obstetrics; PAS, placenta accreta spectrum.\n\nwww.ogscience.org10\nVol. 69, No. 1, 2026\npated during a cesarean hysterectomy. Therefore, meticu -\nlous preoperative preparation, including the availability of \na cell saver and close collaboration with a blood bank for \ntimely transfusion, is essential. Antifibrinolytic agents such as \ntranexamic acid can be administered prophylactically or dur -\ning hemorrhage. A recent large, multicenter, international \nrandomized clinical trial reported that tranexamic acid could \nreduce maternal mortality in PPH [65]. While some reports \nhave suggested a reduction in bleeding when prophylacti -\ncally administered during cesarean deliveries, further research \nis needed in this area.\nA multidisciplinary team must also be readily available to \nmanage potential complications such as bladder or ureteral \ninjury, other organ damage, massive hemorrhage, and infec-\ntion. The utility of prophylactic ureteral stent placement in \nPAS remains controversial, particularly in cases of suspected \nbladder or ureteric invasion. The ACOG and the SMFM do \nnot recommend routine use but advise that ureteral stenting \nbe considered on a case-by-case basis when genitourinary \ntract involvement is suspected, especially in percreta cases \n[32]. A recent systematic review and meta-analysis concluded \nthat prophylactic ureteral stenting did not significantly reduce \nthe incidence of urinary patients with PAS, suggesting a lim-\nited benefit from routine use [66]. These conflicting findings \nhighlight the need for further prospective studies to clarify \nthe role of ureteral stenting in patients with PAS. Taken to -\ngether, although universal prophylactic use is not currently \nendorsed, selected applications in high-risk PAS cases may \nbe a useful adjunct to minimize urological complications. \nIntra-arterial balloon occlusion (IABO) has been increasingly \nused as an adjunctive strategy in the surgical management \nof placenta accreta. By temporarily reducing pelvic arterial \nblood flow, IABO can decrease intraoperative blood loss and \nimprove visualization of the surgical field during cesarean \nhysterectomy. A large observational study from Scandinavia \nreported that IABO during cesarean hysterectomy was as -\nsociated with reduced estimated blood loss and lower trans-\nfusion requirements, although the overall impact on mater -\nnal morbidity remains debated [67]. Despite the potential \nbenefits, risks such as vascular injury, thrombosis, and limb \nischemia must be considered, and its use is generally recom-\nmended in specialized centers with interventional radiology \nexpertise. Anesthesia for surgery was chosen based on the \npatient’s condition and circumstances, including general or \nregional/neuraxial anesthesia. Although general anesthesia is \ngenerally preferred, regional anesthesia (epidural or spinal) is \nincreasingly used. Several studies have indicated that conver-\nsion from regional to general anesthesia due to increased \nblood loss or prolonged surgical time occurs in approximately \n8-45% of cases [68,69]. While neonatal outcomes are re -\nported to be better with regional anesthesia than with gen -\neral anesthesia, maternal outcomes, such as blood loss and \ntransfusion rates, vary across different literature [68-70]. \nFor skin incisions, a midline abdominal incision is gener -\nally preferred to ensure a wide surgical field, although some \noperators, such as Maylard, may opt for transverse incisions. \nThe hysterectomy approach can vary depending on the pla -\ncental location, and it is generally safer to make incisions \nto avoid the placentation site. There was an approximately \n50/50 split in the preference between total and subtotal hys-\nterectomies. Total hysterectomy offers the long-term benefit \nof preventing cervical malignancy, whereas subtotal hysterec-\ntomy may offer advantages in terms of reduced intraopera -\ntive blood loss and recovery. However, in cases of cervical \ninvolvement, such as those with placenta previa, total hyster-\nectomy is a more advisable approach.\n2) Conservative management\nConservative management of PAS is primarily undertaken to \npreserve fertility and maintain the patient’s self-esteem by \navoiding hysterectomy. This approach can be broadly divided \ninto two main strategies: attempting placental removal and \nleaving the placenta in situ within the uterus. Other adjunc -\ntive methods, such as UAE, methotrexate therapy, hemostat-\nic sutures, pelvic devascularization, and balloon tamponade, \nhave also been explored.\n① Uterine preservation and placental removal\nPlacental removal typically involves manual removal, which is \ncommonly encountered when PAS is not diagnosed prena -\ntally. This approach carries a significant risk of massive hem -\norrhage, potentially leading to life-threatening scenarios. If \nbleeding becomes uncontrollable, a subsequent unavoidable \nhysterectomy may be necessary after placental removal. Fur-\nthermore, even if initial bleeding is controlled, rebleeding can \noccur postpartum, necessitating preparedness for additional \nmanagement strategies such as UAE.\n② Excision of the placenta using an in situ approach\nThis method involves leaving the placenta within the uterus \n\nwww.ogscience.org 11\nSul Lee, et al. PAS: clinical insights\nand awaiting spontaneous resorption. A retrospective mul -\nticenter study reported that of 167 cases managed with con-\nservative therapy, 131 women (78.4%; 95% CI, 71.4-84.4%) \nhad successful outcomes, while the remaining 36 underwent \neither primary hysterectomy (18 cases) or delayed hysterec -\ntomy (18 cases). Spontaneous placental resorption occurred \namong 87 out of 116 women (75%; 95% CI, 66.1-82.6%), \nwith a median delay from delivery of approximately 13.5 \nweeks (range 4-60 weeks) [71]. Other studies have reported \nthat approximately 20% of women require hysterectomy af-\nter conservative management [72,73]. \nA retained placenta rarely leads to complications such as \ncoagulopathy or septicemia, necessitating careful monitoring. \nWeekly monitoring of serum β-hCG levels is recommended \nfor the first 2 months, followed by monthly checks to con -\nfirm placental resorption. However, additional MRI is gener -\nally not recommended. Several methods have been proposed \nto aid the resolution of retained placental fragments. One \nmethod involves the administration of methotrexate (MTX). \nA recent observational case series involving 24 women with \nretained placenta in situ who received MTX reported placen-\ntal expulsion in approximately 33.3% of cases, with 55% \nspontaneous and 45% achieved by dilation and curettage \n[74]. However, research is still limited, and considering the \npotential adverse effects of MTX, such as neutropenia and \nmedullary aplasia, its routine use has not yet been recom -\nmended. Hysteroscopic resection has also been proposed for \nremoving retained placental fragments. Although it is gener-\nally successful, its benefit in asymptomatic women remains \nunclear.\nSurgical or radiological uterine devascularization tech -\nniques are employed to reduce PPH in patients with PAS. \nThese methods include bilateral uterine or hypogastric artery \nligation, iliac artery embolization, or balloon occlusion. Pro -\nphylactic embolization reduces intraoperative blood loss and \nsubsequent hemorrhage [75,76]. However, the efficacy of \nprophylactic balloon catheter placement in the iliac arteries \nor aorta in patients with PAS remains controversial.\nObstetrics and fertility outcome\nWomen with successfully preserved uteri may consider fu -\nture pregnancies. However, in those with a history of PAS \ndisorders, the risk of recurrence in subsequent pregnancies \nhas been reported to be approximately 22-29% [77,78]. Ad-\nditionally, intrauterine adhesions and secondary amenorrhea, \nboth of which may impair fertility, were observed in approxi-\nmately 8.3% of these cases [78].\nConclusion\nPAS remains a leading cause of obstetric hemorrhage and \nmaternal morbidity. Its incidence continues to increase, large-\nly in parallel with increasing cesarean delivery rates, uterine \nsurgeries, and assisted reproductive technologies. Antenatal \nrecognition through careful risk assessment and imaging, \nfollowed by referral to centralized high-risk care centers and \nmultidisciplinary management, is critical for improving out -\ncomes. Although conservative options may preserve fertility \nin selected cases, recurrence rates and long-term complica -\ntions remain significant. Future randomized controlled trials \nand longitudinal studies on fertility outcomes are urgently \nrequired to establish optimal management strategies.\nConflict of interest\nNo potential conflict of interest relevant to this article was \nreported.\nEthical approval\nNot applicable.\nPatient consent\nNot applicable.\nFunding information\nThis review article was supported by clinical research funding \nfrom Pusan National University Hospital in 2024.\n\nwww.ogscience.org12\nVol. 69, No. 1, 2026\nReferences\n1. Betrán AP , Ye J, Moller AB, Zhang J, Gülmezoglu AM, \nTorloni MR. 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