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Placenta accreta represents a pathological entity that includes different types of placental implantation anomalies, such as placenta with abnormal adhesion and invasive placenta(1-4).
The term accreta comes from the Latin language (ad + crescere), translated as growth by adherence, adhesion and attachment(5).
Accretization represents the direct adhesion of the villous tissue to the superficial myometrial layer or near the myometrial fibers, with the partial or total absence of basal decidua, the imperfect development of the fibrinoid or the Nitabuch layer(4,6). The partial or total absence of the decidua determines the absence of the physiological cleavage space.
This abnormal decidualization can be either located strictly in a certain area at the level of the implantation site, or the implantation was carried out in a uterine scar area. Therefore, partially or fully, the placental cotyledons become deeply anchored intramyometrial. The extension of the accreted placentation area as well as the depth of invasion are different from case to case(1,6,7).
Classification
1. Placenta accreta – chorionic villi invade the superficial myometrial layer.
2. Placenta increta – the invasion is deep into the myometrium.
3. Placenta percreta – the placenta penetrates through the myometrium and uterine visceral peritoneum into the neighboring viscera, most often in the bladder.
The term placenta accreta has gradually been replaced by “morbidly adherent placenta”(1).
In classical terminology, any situations in the placenta accreta-increta-percreta spectrum is called placenta accreta spectrum (PAS)(2).
Incidence and risk factors
PAS anomalies are now considered iatrogenic conditions, attributed to the increasing rates of caesarean deliveries in the last decade(1,8). More than 90% of PAS cases occur in women with at least one caesarean section delivery in the past, especially in cases with a history of placenta praevia(1,6) (Table 1). Placenta accreta represents approximately 79% of PAS cases, placenta increta represent 14% of PAS cases, and placenta percreta represents 7% of PAS cases(1).
PAS is associated with an increased risk of maternal morbidity and mortality, and therefore this entity requires multidisciplinary care. It represents the most important cause of hemorrhage and emergency peripartum hysterectomy(9).
Diagnosis
The specific symptomatology in the first and second trimesters is hemorrhage, as a result of the coexistence of PAS with placenta praevia or if hematuria is persistent in cases of placenta percreta with extension into the bladder wall. There are situations when pregnant women who don’t associate placenta praevia end up being diagnosed with PAS in the third stage of labor, when placenta with abnormal adhesion is found(1,9).
Diagnostic ultrasound
Ideally, PAS should be diagnosed antepartum in the second trimester, for an optimal conduit in the third trimester(1,9). The examinations by transabdominal and endovaginal ultrasound (Figures 1 and 2) of the placenta, in combination with color Doppler ultrasound of placental blood flow and power Doppler, represent valuable tools for the diagnosis of PAS(1,2,4,9).
To establish the diagnosis, the definitions accepted by the European Working Group on Abnormally Invasive Placenta are used(2).
PAS is suspected in the situations presented in Table 2(1,2,9).
Although it is a recent technical acquisition, three-dimensional ultrasound is a very useful tool in the diagnosis of PAS(10).
MRI diagnosis
The role of magnetic resonance imaging (MRI) in the diagnosis of PAS is comparable to that of two-dimensional ultrasound corroborated with color Doppler, performed by specialists with expertise in imaging(2,11). It has a limited role in pregnancies below 24 weeks of amenorrhea(12).
MRI is not recommended as a primary diagnostic tool, but as an adjunct to ultrasound, when the ultrasound results are equivocal, inconclusive. It’s a valuable tool in the evaluation of the anatomy, of the degree of myometrial invasion, the invasion of the ureters, the urinary bladder or the parameters, in the posterior placental locations(1,2,9).
The MRI elements that establish the diagnosis of PAS are presented in Table 3(1,9).
The timely confirmation of the PAS diagnosis is vital in order to plan the birth.
Therapeutic behavior
The therapeutic behavior in case of PAS is planned according to the same principles as those described in case of placenta praevia.
Preterm birth must be anticipated in symptomatic pregnant women, so the administration of antenatal corticosteroids to accelerate fetal lung maturation can be performed starting at 24 weeks of amenorrhea(1).
The basic principle is to plan the birth, to avoid an emergency caesarean section. Current recommendations are for elective delivery at 35-36 weeks of amenorrhea(1,2,4,8). Delivery under 34 weeks of amenorrhea is an option in pregnant women with recurrent episodes of vaginal bleeding, especially in cases of placenta percreta with invasion of the neighborhood viscera(1,8).
The recommended surgical approach is through a median incision, to allow easy conversion from caesarean section to necessary hysterectomy(8). The hysterotomy should be performed in such a way as to avoid the placenta. After the extraction of the fetus, extraction of the placenta is attempted. If abnormal adhesion is found, it is recommended to perform hysterorrhaphy and then perform necessary hysterectomy. This approach minimizes the risk of intraoperative hemorrhage(8). There are cases when it is useful to leave the placenta in its insertion area and perform the hysterectomy in a second time, as it has been reported to decrease the volume of intraoperative bleeding and the need for a massive transfusion(8,13). For women who wish to preserve fertility and only if possible intraoperatively, the placenta can be abandoned in situ, with or without the adjuvant use of methotrexate(14).
Intraoperatively, careful monitoring of hemodynamic balance, blood loss, and evaluation of hemoglobin, blood gases, electrolytes and coagulation factors are necessary. Current protocols recommend a 1:1:1 transfusion of red blood cell mass – fresh frozen plasma – platelets, antifibrinolytic therapy in the first three hours after birth (1 gram of tranexamic acid intravenous)(8,15,16).
Differential diagnosis
Although all the entities discussed belong to PAS, it’s vital to make the differential diagnosis between placenta accreta, increta and percreta. The stage diagnosis of the invasion of neighboring organs is essential before the planned surgical intervention(15).
Prognosis and complications
The prognosis is better for pregnant women with placenta accreta without placenta praevia. Accreted placenta praevia has a higher risk of intraoperative bleeding, requiring hysterectomy for hemostasis, thus increasing maternal morbidity(17).
Pregnant women with placenta percreta have a higher risk of complications compared to those with placenta accreta or placenta increta, due to the higher risk of damage to the neighboring organs, most commonly the bladder and ureters(8). n
Conflict of interests: The authors declare no conflict of interests.