Placenta accreta spectrum disorders (PAS) refer to a group of conditions in which the placental villi abnormally invade part or all of the uterine myometrium.
Based on the depth of invasion of the placental villi into the uterine myometrium, PAS can be classified as:
- Placenta accreta: The placental villi adhere to the surface of the uterine myometrium.
- Placenta increta: The placental villi penetrate into the uterine myometrium.
- Placenta percreta: The placental villi penetrate through the uterine myometrium, reaching or exceeding the uterine serosa.
Figure 1 Classification of placenta accreta spectrum disorders
It can also be classified based on the area of implantation into complete placental implantation and partial placental implantation.
Placenta accreta spectrum disorders may result in severe postpartum hemorrhage, hypovolemic shock, and may lead to hysterectomy. In severe cases, it can even result in maternal death. Additionally, the incidence of puerperal infection is increased. Common high-risk factors include placenta previa, a history of cesarean delivery, a history of myomectomy, a history of uterine perforation, a history of placental implantation, multiple miscarriages, advanced maternal age, and others.
Clinical Features and Diagnosis
There are no typical clinical features, but they may present as vaginal bleeding associated with placenta previa. Diagnostic efforts rely on the identification of high-risk factors along with ultrasound and/or magnetic resonance imaging (MRI). Definitive diagnosis depends on surgical findings during delivery or postpartum pathological evaluation.
Clinical Features
The primary manifestation involves failure of the placenta to separate more than 30 minutes after fetal delivery, with or without vaginal bleeding. Manual attempts at placental removal reveal difficulty with detachment, or a seamless and firm adhesion of the placenta to the uterine wall. During cesarean delivery, placental implantation may be observed, with penetration into or through the uterine myometrium.
Imaging Examination
Color Doppler ultrasound is the most commonly used method for assessing placental location and implantation. Ultrasound findings may indicate disruption of normal placental architecture, diffuse or focal vascular lacunae within the placenta, thinning or absence of the normal hypoechoic zone behind the placenta, and abundant vasculature at the uterine serosa-bladder junction. MRI is frequently used to evaluate posterior uterine wall implantation, the depth of placental invasion into the myometrium, involvement of adjacent tissues and the bladder, or in cases of highly suspicious PAS not confirmed by ultrasound.
Management
Placenta accreta spectrum disorders are a significant cause of both antepartum and postpartum hemorrhage. In cases where PAS is diagnosed during pregnancy, patients must be fully informed of the risks of poor pregnancy outcomes. Facilities unable to provide appropriate follow-up or management conditions should transfer patients to higher-level centers promptly. A multidisciplinary team approach, along with adequate monitoring and skills training, may improve pregnancy outcomes in affected individuals.
Prenatal Management
Prevention and correction of anemia are prioritized, with a recommendation to increase the frequency of ultrasound examinations to evaluate placental location, depth of placental implantation, and fetal development.
Time to Delivery
For patients in stable condition, pregnancy termination is typically planned between 34–37 weeks of gestation. If the condition significantly endangers maternal or fetal life, immediate termination of pregnancy may be required regardless of gestational age.
Mode of Delivery
Planned delivery is commonly utilized for patients with PAS, often via cesarean section. Patients without placenta previa and without indications for cesarean section may attempt a trial of vaginal delivery.
Cesarean Preoperative Evaluation
A multidisciplinary diagnostic and treatment team is assembled, with comprehensive preparation of blood products, surgical instruments, and other necessary resources.
Surgical Approach
The uterine incision depends on the location of placental attachment and generally avoids the placenta or the main bulk of placental tissue. Diverse hemostatic measures may be employed intraoperatively, with prophylactic antibiotics administered postoperatively. The optimal management strategy is based on intraoperative findings and surgical progress. Placental in situ preservation, if performed, requires careful consideration.