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Placenta accreta spectrum (PAS) refers to an atypical adherence of villous tissue to the uterine wall and includes the medical conditions of placenta accreta, increta, and percreta. PAS can result in significant bleeding and may necessitate perinatal hysterectomy, increasing the likelihood of maternal mortality.
The first step in diagnosing prenatal PAS is to identify maternal risk factors. Previous cesarean delivery (CD) is considered one of the most significant risk factors, particularly when combined with placenta previa or multiple previous CD deliveries. The prevailing hypothesis about the etiology of PAS over the past few decades has been that damage to the endometrial-myometrial interface causes the failure of normal decidualization of the uterine scar area, leading to the loss of sub-decidual myometrium, allowing for abnormal deep placental villi anchoring and trophoblast infiltration. Various studies have demonstrated that disruptions to the uterine cavity can result in damage to the endometrial-myometrial interface, thereby affecting the development of uterine scar tissue and increasing the likelihood of PAS. However, this hypothesis cannot entirely explain the rare occurrence of PAS in women who have not undergone any previous uterine surgery.1
Reports of PAS are rare in women who have not previously been pregnant and have no significant damage to the myometrium. However, PAS often goes undiagnosed in half to two-thirds of cases before delivery, which further increases maternal risk. The first recorded case of placenta accreta was in 1927 by Dr D.S. Förster in a patient who had no prior uterine surgery but had previously experienced placental retention during three vaginal births. During her fourth delivery, the patient developed PAS and hemorrhaged during a failed attempt to deliver the placenta, resulting in a hysterectomy. While some studies have shown that placenta previa (PP) covered with a uterine scar leads to more postpartum bleeding compared to PP without a uterine scar, it is crucial to improve awareness of PAS clinical management in non-uterine scar sites to improve overall outcomes for patients with PAS.
In China, a range of medical procedures are common for childbearing age women, including induced abortion, curettage for incomplete abortion or retained placenta, hysteroscopy for endometrial polypectomy, and diagnosis of infertility. These surgeries are often performed under anesthesia, and surgical instruments such as electric cutters or curettes may inadvertently penetrate the myometrium, causing undetected perforations that can result in permanent myometrial defects and uterine scars. These injuries can lead to serious conditions such as PAS and prenatal uterine rupture.
To prevent these complications, healthcare providers need to be vigilant and focus on identifying risk factors beyond a history of previous cesarean delivery or uterine surgery. Other factors that warrant attention include multiparity, placenta previa, advanced maternal age, twin gestation, prior postpartum hemorrhage (PPH) or PAS, prior cesarean scar pregnancy (CSP), prior curettage or manual placental extraction, and a history of hysteroscopy. By considering these factors and taking appropriate measures to prevent uterine scarring, healthcare providers can reduce the risk of PAS and other serious complications in childbearing age women.
In addition to obtaining a comprehensive medical history and identifying high-risk factors for PAS, it is essential to strengthen the capacity of healthcare providers in identifying ultrasound images of PAS. Currently, Doppler techniques, including grayscale ultrasound and color Doppler modalities, are preferred for prenatal diagnosis of placental anomalies. The Doppler ultrasound imaging of PAS may reveal lacuna, abnormal uteroplacental interface, abnormal uterine contour (placental bulge), exophytic mass, bridging vessel, and the presence of cervical blood sinus. Among these, the best indicators for predicting PAS are placental lacuna, loss of the uteroplacental interface, and dilated bulging vessels in the uterus–bladder interface. Some studies suggest that a low-lying placenta in the first trimester (where the gestational sac is located close to the internal cervical os and/or the placental implantation is behind the partially filled maternal bladder) may progress to PAS. Other studies have found that placentas with large areas and/or located in the cervix or uterine horn are more likely to develop PAS.2–6 Therefore, it is important for healthcare providers to pay attention to abnormalities in the attachment site and area of the placenta, especially in pregnant women who have not had previous uterine scars. By identifying these abnormalities early on and taking appropriate measures, healthcare providers can prevent serious complications and improve maternal and fetal outcomes.
Our team has developed a valuable tool for diagnosing PAS called the “Placenta Accreta Spectrum Ultrasound Scoring System” (PASUSS) (Table 1).5 This system can be used to estimate the severity of PAS when there are clinical high-risk factors or a Doppler ultrasound result suspecting PAS. Patients who have high-risk factors for PAS should undergo specialized Doppler ultrasound imaging by experienced prenatal diagnosis providers. According to the American College of Obstetricians and Gynecologists (ACOG), ultrasound examinations should be performed at 18–20 weeks, 28–30 weeks, and 32–34 weeks of pregnancy for high-risk patients with PAS. However, the optimal timing and frequency of ultrasound examination are still unclear. Pelvic Magnetic resonance imaging (MRI) may be considered if necessary, but it is not routinely recommended. All facilities have implemented plans to manage PAS cases and aim to transfer patients to a tertiary hospital based on pre-established institutional agreements. Additionally, attention is given to the anemia and malnutrition of pregnant women. If necessary, oral replacement or intravenous infusions for iron deficiency can be administered.6,7
Optimal management of antenatally diagnosed PAS is achieved by transferring the patient to a tertiary hospital with considerable experience and a comprehensive multidisciplinary care team. This consistent team can assist in proper preparation for potential complications and delivery. For instance, blood banks can be informed for large volume transfusions, pediatrics for neonatal resuscitation, and vascular interventions for angioembolism. Given the significant risk of maternal morbidity and mortality, it is crucial to determine the appropriate timing and mode of pregnancy termination. The decision of delivery timing is based on the balance of maternal risks and neonatal benefits. Some guidelines recommend scheduling a cesarean section or hysterectomy between 34 0/7 and 35 6/7 weeks for stable patients. However, early delivery may be required in the event of placenta previa, persistent vaginal bleeding, preeclampsia, fetal compromise, or occurrence of maternal comorbidities.
Antenatal glucocorticoids are necessary to promote fetal lung maturation at this point. Our hospital's findings suggest that pregnancy can be terminated at 37 weeks for women with a PASUSS score of less than 10 points.4,5 The appropriate delivery timing for patients with accreta placentation in non-uterine scar sites or without uterine scar has not been thoroughly studied, and it is yet to be determined whether it is safe to wait beyond 37 weeks of gestation while under close monitoring. Pregnant women diagnosed with PAS can attempt vaginal delivery unless there are other maternal indications for cesarean delivery or placenta previa. Cesarean delivery is preferred if there are other indications for cesarean delivery or placenta previa. Pregnant women and their families should be well informed about the risks, including PPH and hysterectomy, as well as the choice of delivery mode before the anticipated delivery.
PAS often goes undiagnosed in about half to two-thirds of cases before delivery, which increases the maternal risk. It may be unexpectedly recognized during cesarean or vaginal delivery, based on the appearance of the uterus. In such cases, delivery should be temporarily postponed until the best surgical expertise is obtained, unless immediate delivery is required for medical reasons. When PAS is discovered after uterine opening during surgery, the same surgical principles apply as for preoperatively diagnosed PAS. If there are placental adhesions or retention during vaginal delivery, the medical history should be reviewed, and caution should be exercised for PAS. After vaginal delivery, attempting to forcibly remove the implanted placenta can result in massive hemorrhage, which should be avoided. Instead, curettage and placenta removal should be performed under ultrasound guidance to prevent uterine inversion or perforation. In cases of sustained or uncontrolled bleeding, interventional radiology embolization of the uterine artery may be helpful, but it can be difficult to perform surgery in unstable patients. Tranexamic acid can be used for antifibrinolytic therapy in cases of postpartum hemorrhage.
PAS has become increasingly prevalent in recent years, and is associated with significant maternal morbidity and mortality. Early detection and diagnosis of PAS can be aided by a thorough understanding of risk factors and prenatal imaging. Effective management of PAS requires a multidisciplinary approach, involving a team of healthcare professionals. Our experience and management strategies can provide valuable insights for the treatment of PAS in cases where there is no uterine scar coverage.
Conflict of interest
The authors declare that they have no competing interests.
Funding
National Key Research and Development Program of China (2021YFC2701500).