Placenta accreta is a histopathologic term that refers to an obstetrical condition in which the placenta will not detach normally from the uterine wall at delivery due to the abnormal attachment or invasion of the villi into the myometrium(1-3). The term placenta accreta was initially used by Baisch at the beginning of the 19th century and it was first described by Irving et al. in 1937(4,5). It is a very serious pathology that might lead to tragic consequences, especially for the mother, being associated with massive peripartum hemorrhage(5).
In terms of histopathology, abnormal placentation could take many forms depending on the depth of the invasion in the uterine wall, namely: placenta adherenta/creta/vera (the villi adhere to the uterine wall without penetrating it), placenta increta (the villi invade the myometrium) and placenta percreta (the villi invade all layers of the uterine wall, through the serosa, with possible invasion of adjacent organs)(1-3). The International Federation of Gynecology and Obstetrics (FIGO) recently proposed a new standardized terminology named placenta accreta spectrum (PAS) disorders, encompassing all of the aforementioned terms(2).
During the last decades, there has been a significant rise worldwide in the prevalence of PAS disorders and the most incriminated factor is the global elevated caesarean deliveries (CD) rates, leading to a nearly 10-fold increase(3,6,7). Additionally, the risk increases proportionally to the number of previous caesarean deliveries, from 11% after one caesarean delivery to nearly 60% after the third one(8).
One theory that explains the occurrence of PAS disorders is related to the importance of decidua which plays the important role of hampering abnormal placentation, therefore the absence of the decidua in the scarred uterus leads to deep infiltration of the trophoblast into the uterine wall(5,6,9). This theory is supported by the physiopathology of ectopic pregnancy, where the lack of decidua leads to invasive implantation of the trophoblast into the fallopian tube wall or the abdomen(10). In the majority of cases, the uterine scar is an iatrogenic defect following a CD; however, uterine curettage, manual removal of the placenta or endometritis can easily be incriminated as well(6). Changes in the uterine structure after a CD consist of appearance of an avascular tissue (e.g., the scar), a deficient endometrium repair and impaired vascularization around the damaged area(10,11). All these alterations allow an abnormal extensive penetration into the myometrium(10). It is worth mentioning that PAS can also affect primipara, women with no previous uterine procedures, and the involved pathologies are, as follows, bicornuate uterus, adenomyosis or submucosal fibroma(3).
As previously mentioned, the most incriminated risk factor for PAS disorders is a previous CD, whereas the combination of placenta praevia and a history of caesarean operation constitutes the highest risk for anomalous placentation(3,6,12). It must be admitted that CD is not solely responsible for generating a uterine scar, myomectomy, hysteroscopic procedures, uterine curettage, manual removal of the placenta, endometrial ablation, uterine artery embolization being similarly responsible(4,6). Moreover, in vitro fertilization (IVF) procedures, advanced maternal age, multiparity, Asherman syndrome, postpartum endometritis or PAS disorders diagnosed in a previous pregnancy are mentioned to be additional risk factors(3,4,6,13).
It is of greatest importance to be aware of the potentially tragic complications this pathology brings along, therefore prenatal diagnosis of PAS disorders is essential. Although it might be challenging, it allows the physician to properly organize a multidisciplinary team and to plan the delivery with the purpose of reducing perioperative complications(1,4,6,14). Notwithstanding, it has been observed that almost half to two thirds of PAS cases failed to be discovered before delivery(1,4). Therefore, it is imperative to identify patients at risk, and in the presence of specific risk factors, namely history of CD or placenta praevia, it is highly recommended to refer these women to a tertiary care center in order to be evaluated(6,10).
Managing a case of PAS disorder can be demanding. FIGO and the American College of Obstetrics and Gynecology (ACOG) recommends caesarean hysterectomy with placenta in situ; in addition, several conservative methods are accepted, although these should be taken into account only in thoroughly selected cases(2,4,10,15).
Materials and method
We conducted a literature search in the PubMed, Embase and Medline databases in order to identify relevant information for this paper. We used the following search terms: “adherent placenta after caesarean section”, “placenta accreta”, “complications of caesarean delivery”, “caesarean scar and placenta accreta”, “diagnosis of placenta accreta”, “management of abnormal placentation”, “risk factors for placenta accreta”. We found relevant articles published between 2017 and 2022, assessing the complexity of abnormal placentation cases and their management, risk factors implicated in this pathology, possible complications of caesarean delivery for future pregnancies and challenges in antenatal diagnosis of placenta accreta spectrum disorders. In the end, 23 articles that met our criteria were found relevant for this publication.
Diagnostic challenges in PAS
Placenta accreta spectrum disorders consist of the three entities: placenta accreta, placenta increta and placenta percreta, all of which referring to the histopathological features. In this regard, we can most certainly consider histopathological examination as gold standard in PAS diagnosis, while imaging techniques only guide the clinician and raise the suspicion of PAS(3,4). At the same time, the opportunity to be aware of the possibility of this condition before the time of delivery comes in significant support, as it can reduce maternal morbidity and mortality(1,4). In order to elaborate individual management plans for pregnant women suffering from PAS disorders, physicians must identify patients at risk for developing this pathology with the purpose of correctly assessing them(1,2,4,6,10). Therefore, PAS disorders can be diagnosed during pregnancy and thus offering the clinician the opportunity to meticulously plan the delivery, or at birth, as it happens in a significant number of cases, putting the physician in a pressing and critical situation.
Ultrasound (US) evaluation is considered by FIGO and ACOG to be the imaging technique of choice in diagnosing PAS disorders(2,3,10). A precise antenatal diagnosis of PAS depends on the clinician’s experience, equipment and also on scanning conditions(6,10). Although in most patients the ultrasonographic signs of PAS are discovered during the second and third trimesters, some authors acknowledge that PAS disorders can be suspected even from the first trimester and the suspicion is high if the gestational sac is located adjacent to the caesarean scar or to the lower uterine segment(3). There are some ultrasonographic features associated to PAS disorders described in medical literature, namely: placental vascular lacunae, absence of clear zone, thinning of the myometrium, discontinuation of the bladder wall, placental bulging or focal exophytic mass(3,6). Moreover, color Doppler imaging gives the opportunity to identify vascular and circulatory anomalies suggesting PAS disorders(3). It is common knowledge that US, even though it is considered to be the first-line investigation, does not always offer conclusive information. Some cases need further extensive imaging techniques, such as magnetic resonance imaging (MRI)(10,16). MRI has proven its usefulness when there is a high suspicion of PAS disorder at the US and further detailed images are needed in order to assess the depth of the myometrium and the parametrial invasion, as well as extension to neighboring organs(3,4,6,10). Likewise, this imaging tool is very efficient in cases of disadvantageous placental position (such as on the posterior wall of the uterus) and if the patient’s Body Mass Index is rather high(3,4,6,10). It is presumed that the appropriate gestational age to do an MRI screening for PAS is between 24 and 30 weeks of gestation(3). There are data in the medical literature acknowledging the superiority of MRI over US in certain circumstances, though in terms of cost-effectiveness and accessibility US remains the method of choice and MRI screening should be recommended to patients presenting a high risk and ultrasonographic signs of PAS(4,6,10).
Physicians must be aware of the possibility of false positive, as well as of the false negative antenatal diagnosis of PAS disorders, because these may lead to tragic scenarios due to morbid peripartum and postpartum complications caused by unnecessary or inaccurate medical steps(1).
When there is no antenatal diagnosis or suspicion of PAS disorders, they can be unexpectedly discovered intrapartum, during vaginal or caesarean delivery. There are macroscopic signs that can be observed when entering the peritoneal cavity during CD, such as: protrusion of the placenta causing a blueish aspect of uterine wall or visible invasion of the placenta through the uterine wall, with or without penetration of the serosa; moreover, in the absence of macroscopic evidence, if spontaneous placental detachment does not occur, the physician can consider applying a little traction on the umbilical cord or even a digital examination and if “dimple sign” appears or there is no detectable cleavage plan between the uterine wall and an area or even all of the placental tissue, PAS disorder can be diagnosed(4,6,15). The attempt of manual removal of the placenta will cause a substantial hemorrhage. Likewise, the absence of spontaneous placental delivery albeit active management or retained placental tissue necessitating uterine curettage after vaginal birth constitute PAS disorder signs(3,4,6,10).
As previously mentioned, the histopathologic examination is the gold standard in PAS disorder diagnosis. However, there is an important observation to be made: this investigation can only be made if there is tissue to be examined, which means that if the surgical team decides on conservative management, with the placenta being left in situ, there will be no certain diagnosis(4,15).
Management of PAS disorders
Managing one case of PAS disorder refers not only to the intrapartum surgical techniques and decisions, but it encompasses all the information, investigations and counseling the patient receives during pregnancy from the moment PAS is suspected. Undoubtedly, there are cases of “unexpected PAS”, when neither the medical team, nor the patient has knowledge of the existence of this pathology and under-pressure medical decisions are needed(10).
Counseling the pregnant patients and their families about this pathology when suspected antenatal is common sense. They must be aware of the potential complications that might occur during pregnancy and delivery. Even though there is the alternative of fertility preservation, they must be correctly informed regarding the possible need for caesarean hysterectomy, blood transfusion or intensive care unit admission, as well as the necessity for postoperative thoroughly follow-up(1,10,17).
The optimal management of PAS disorders requires a multidisciplinary team and a tertiary medical center able to deal with these complex cases(2). As far as surgical techniques are concerned, both radical and conservative methods are described. The ground rule when facing this pathology, regardless the surgical approach, is never to attempt to separate the placenta, in order to avoid an uncontrolled massive obstetrical bleeding(6,10,17). Radical techniques are caesarean hysterectomy and delayed hysterectomy; they stand for the definitive surgical treatment and the only difference between these methods refers to the moment the uterus is removed – during caesarean operation or several weeks later(4,6). Caesarean hysterectomy with the placenta left in situ is generally accepted as gold standard in cases of invasive placentation, according to ACOG(4,6,15). Nonetheless, it is a procedure with a significantly high morbidity and mortality rate, up to 40-50% and 7%, respectively, due massive or uncontrollable hemorrhage, as well as to injury of adjacent pelvic organs(6,10). On the other hand, delayed hysterectomy must be taken into account when challenging surgical steps are required consequently to the invasion of placenta into the surrounding tissues, with the purpose of diminishing uterine vascularity in addition to uterine involution, creating the premises for a safer surgical procedure, with less potential hemorrhagic complications(4,6). Furthermore, delayed hysterectomy is to be considered in the event of accidentally discovering PAS disorder by a not sufficiently experienced medical team(4).
The conservative management of PAS disorders is a feasible technique for women with strong desire for fertility preservation, but also in extreme situations, when massive bleeding is expected in case of peripartum hysterectomy(4,6,10). There are three methods according to FIGO guidelines: the expectant approach, where the placenta is left in situ, expecting its spontaneous resorption; the one-step procedure, consisting of the resection of affected myometrium and uterus reconstruction; and the triple-P procedure(2,15). An important aspect during the conservative procedures is related to the use of uterotonic substances, which should be avoided since they might provoke heavy bleeding by hampering the detachment of the unaffected parts of the placenta(3,10).
Another matter of importance is referring to the optimum timing for delivery in case of PAS disorders. Although there is still no consensus on this subject, various authors find appropriate elective delivery from 34 to 36+ weeks of gestation, depending on the case(3,4,6). It is considered that for patients experiencing unimportant but frequent episodes of vaginal bleeding throughout pregnancy or a single major vaginal bleeding event, patients with history of preterm delivery, suffering from preeclampsia, presenting with premature rupture of the membranes, uterine contractions or any sign of fetal distress, the delivery should be planned at around 34 weeks of gestation(3,6). By contrast, elective caesarean should be planned close to 36+ weeks of gestation in stable patients, who do not meet the aforementioned criteria(6). It is worth considering the need for corticosteroids administration for fetal lung maturation depending on regional protocols(2,6,10). Moreover, if the conservative management is intended, the delivery must not be delayed beyond 36 weeks of gestation, taking into account the considerable risk of abundant bleeding after this gestational age, event which will require an emergency delivery(10).
Caesarean delivery has lately become a trending phenomenon all over the world, CS registering an alarming increased rate(18,19). Therefore, we must expect a growing incidence of potential immediate or long-term complications, among which we mention infections, hemorrhage, hysterectomy, infertility, abnormal placentation, uterine rupture, uterine scar defects or ectopic pregnancy(18-21). The long-term complications should not be overlooked due to the potential dramatic consequences in a future pregnancy.
Studies have been conducted concerning whether the incidence of PAS disorders is influenced by the mode of first CS(21,22). Colmorn et al. published a study in 2017 regarding severe obstetric complications at birth after a first elective or emergency caesarean. They described a significantly high incidence of obstetrical complications (97%) after a first caesarean delivery. Also, this article shows that uterine rupture, massive hemorrhage and incidence of PAS disorders were higher after an elective CS. Their results indicate a fourfold risk of abnormal placentation and a twofold risk of uterine rupture in the second pregnancy, after an initial elective CS, when compared with a first emergency caesarean.
In 2018, another paper was published by Shi et al. assessing the same theory(22). Their results were similar to those of Colmorn et al., with a threefold risk of placenta accreta in a subsequent pregnancy for women whose first CS was performed before labor onset, compared to patients whose primary delivery was by emergency caesarean. One possible hypothesis they mention refers to the thickness of the myometrium and its capacity to heal. Therefore, during labor uterus passes through several stages and, due to contractions, the myometrium gets thinner, leading to a potential shortening of the wound, a reduced damage to the uterine wall and a greater healing capability. Another premise concerned immunological changes, meaning that labor initiates an immune response which activates the uterine healing process after a CS. If the stimulus is absent – e.g., uterine contractions, the uterine activation will not occur and abnormal placentation might develop in the future pregnancy.
Alongside PAS disorders, uterine rupture is one of the most severe and common consequences of CS and, more importantly, these two entities can occur simultaneously. In 2020, Akhade et al. published a case report presenting the sudden death of a young female due to uterine scar rupture at the site of abnormal placenta(23). She presented risk factors such as two previous CS and a short period of time between pregnancies (six months). Therefore, in order to prevent additional severe or even life-threatening complications, it is recommended an inter-pregnancy interval of at least one year(23).
With reference to future pregnancies, women who had a successful conservative management have no contraindication for it, although they must be thoroughly informed about the risks and benefits, especially about the high risk of developing PAS disorder again(15,19).
By way of conclusion, during the last few decades there has been a growing concern about the increasing rate of CS, particularly caesareans on maternal demand, which has been proven to be the leading cause of abnormal placentation in future pregnancy. Moreover, it is a fact that the risk of PAS disorders becomes higher with every CS. Studies have shown a greater risk of abnormal placentation after elective CS compared to emergency CS, hence women must be carefully counseled regarding the risk and benefits of both vaginal and caesarean delivery and encouraged to choose vaginal birth over CS if no contraindications exist.
Furthermore, studies have shown the importance of antenatal diagnosis of PAS disorders in managing these complex cases properly. There are still needed future research in order to reach a consensus regarding PAS screening guidelines. For the time being, it is important that women with a high risk for PAS are identified and later on scanned echographically and by MRI in case of inconclusive US images.
Ultimately, women with PAS disorders are preferable to be referred during pregnancy and delivery to a center of excellence where there is a multidisciplinary medical team, whose members are specialized in managing such complex pregnancies as the ones affected by abnormal placentation.
Conflict of interests: The authors declare no conflict of interests.