Placenta Accreta Spectrum: Prenatal Diagnosis And Surgical Planning
Placenta accreta spectrum (PAS) describes abnormal placental attachment and invasion into the uterine wall. It ranges from accreta, in which chorionic villi attach abnormally, to increta, where they invade the myometrium, and percreta, where invasion may extend through the serosa or into nearby organs. The condition can cause severe obstetric hemorrhage, particularly during attempted placental removal or cesarean delivery.
Antenatal recognition changes the entire care pathway. Imaging findings help determine the likelihood and extent of invasion, while maternal history, placental location, previous uterine surgery, and delivery planning establish the level of risk. The objective is not simply to assign a diagnostic label, but to create a safe, coordinated plan for birth, blood loss prevention, anesthesia, and possible pelvic surgery.
For clinicians working in perinatal medicine, PAS management reflects the value of multidisciplinary communication. The scientific focus associated with FAOPS 2020 included perinatal and neonatal medicine, fields in which structured assessment and coordinated decision-making are central to better outcomes.
Recognizing The Clinical Risk
The strongest clinical predictors of PAS are placenta previa or a low-lying placenta combined with a previous cesarean delivery. Risk rises with the number of prior cesareans, especially when the placenta overlies or approaches the cesarean scar. Previous myomectomy, operative hysteroscopy, endometrial curettage, Asherman syndrome, and assisted reproductive technology may add risk, although the degree of association varies.
A careful review of the medical and obstetric history should occur early in pregnancy. The location of the placenta can be assessed during routine ultrasound, with targeted evaluation when it is low-lying, anterior over a scar, or associated with other risk factors. A normal early scan does not eliminate concern if placental migration, scar anatomy, or later sonographic features raise suspicion.
Clinical risk and imaging should be interpreted together. A patient with significant risk factors may require specialist review even when the scan is equivocal, while a highly suspicious ultrasound in a patient without an obvious history still warrants referral. This combined approach reduces the chance that a difficult diagnosis will be discovered only at delivery.
Ultrasound As The Primary Assessment
Targeted obstetric ultrasound is the first-line imaging method for suspected PAS. Transabdominal and transvaginal approaches can complement one another, particularly when the placenta is low, anterior, posterior, or near the cervix. Gray-scale and color Doppler assessment should be systematic rather than based on a single sign.
Features that may suggest PAS include loss or irregularity of the clear zone behind the placenta, interruption of the hypoechoic myometrial layer, placental lacunae with turbulent flow, increased vascularity at the uterine-bladder interface, bridging vessels, and placental tissue extending beyond the uterine contour. Bulging of the lower uterine segment and abnormal vessels in the parametrial region can indicate more extensive disease.
No individual sign is perfectly sensitive or specific. Interpretation is affected by gestational age, placental position, bladder filling, maternal body habitus, prior surgical anatomy, and operator experience. A standardized report should describe placental location, relationship to the scar and cervix, depth of suspected invasion, bladder or parametrial involvement, and the confidence level of the examiner.
The purpose of ultrasound is also practical. It helps determine whether a patient should be referred to a PAS center, whether additional imaging may clarify anatomy, and whether delivery should be scheduled earlier with blood products and specialist teams immediately available.
When Magnetic Resonance Imaging Adds Value
MRI is generally an adjunct rather than a replacement for expert ultrasound. It can be useful when the placenta is posterior or lateral, when ultrasound visualization is limited, or when the suspected invasion extends toward the bladder, pelvic sidewall, cervix, or parametria. MRI may provide a broader anatomical field and assist surgical mapping in complex cases.
Radiologists evaluate placental signal heterogeneity, dark intraplacental bands, uterine bulging, disruption of the uterine contour, abnormal vessels, and extension into adjacent structures. MRI findings should be interpreted in the context of gestational age and prior cesarean-related changes, since normal placental variation can resemble disease.
Imaging specialists who routinely assess fetal and placental anatomy can improve the value of MRI by using a focused protocol and communicating directly with obstetric surgeons. The broader principles of choosing the right modality and linking imaging findings to clinical decisions are also illustrated by fetal MRI applications, although PAS requires its own pregnancy-specific interpretation.
| Planning Element | Key Questions | Effect On Care |
|---|---|---|
| Maternal history | Prior cesarean, uterine surgery, placenta previa, curettage, or assisted reproduction? | Determines baseline risk and referral urgency |
| Placental location | Is the placenta anterior, posterior, low-lying, or covering the cervix? | Guides targeted imaging and operative access |
| Ultrasound findings | Are there lacunae, bridging vessels, loss of the clear zone, or uterine bulging? | Estimates likelihood and possible invasion depth |
| MRI assessment | Is ultrasound limited or are extrauterine structures involved? | Helps map complex pelvic anatomy |
| Surgical preparation | Is a hysterectomy likely, and could bladder or vascular surgery be required? | Determines team composition, consent, and equipment |
| Hemorrhage readiness | Are blood products, cell salvage, massive transfusion protocols, and postoperative care available? | Reduces delay during major obstetric bleeding |
Translating Imaging Into A Surgical Plan
A PAS diagnosis should trigger a coordinated plan rather than an isolated imaging report. The core team commonly includes a maternal-fetal medicine specialist, experienced obstetric surgeon, anesthesiologist, transfusion medicine specialist, neonatologist, radiologist, and operating room personnel. Urology, interventional radiology, vascular surgery, or gynecologic oncology may be involved when imaging suggests bladder, ureteric, parametrial, or pelvic sidewall disease.
For many patients with confirmed or strongly suspected PAS, planned cesarean hysterectomy with the placenta left undisturbed is the established surgical approach. Attempting manual placental separation can provoke rapid, life-threatening hemorrhage. Conservative or fertility-preserving strategies may be considered selectively in highly specialized settings, but they require extensive counseling about delayed hemorrhage, infection, reoperation, thrombosis, and prolonged follow-up.
The operative plan should specify the preferred uterine incision, especially when the placenta occupies the lower anterior uterine segment. Surgeons may choose a fundal or high transverse incision to avoid cutting through the placenta, depending on fetal position and uterine anatomy. Imaging should also inform the expected dissection plane, the possibility of bladder repair, ureteric identification, and the need for additional surgical expertise.
Timing is individualized according to bleeding, labor, rupture of membranes, fetal maturity, maternal comorbidities, and local expertise. Planned delivery before spontaneous labor or significant bleeding is often considered for stable patients, with antenatal corticosteroids when clinically appropriate. The schedule must remain flexible because antepartum hemorrhage, contractions, or membrane rupture may require urgent delivery.
Preparing For Hemorrhage And Neonatal Care
PAS surgery can involve major blood loss even when diagnosis and planning are excellent. Preparation should include type and crossmatch, rapid access to blood components, a massive transfusion protocol, large-bore intravenous access, arterial monitoring when appropriate, and a clearly assigned anesthesia strategy. Cell salvage may be useful where available and supported by institutional practice.
The team should discuss transfusion thresholds, fibrinogen replacement, calcium management, warming, coagulation testing, and the location of critical equipment before the operation begins. A separate plan is needed for postoperative intensive care, pain control, thromboprophylaxis, renal monitoring, and recognition of delayed bleeding or infection.
Neonatal planning is equally important because delivery may occur preterm and the operation can be prolonged. Neonatology should be present or immediately available, with preparation for respiratory support, thermal management, vascular access, and transfer to a neonatal intensive care unit. The wider role of advanced imaging in newborn assessment is reflected in resources on neonatal ultrasound and MRI, which emphasize how imaging contributes to coordinated perinatal care.
Counseling should be direct and compassionate. Families need to understand the likelihood of hysterectomy, possible loss of fertility, blood transfusion, urinary tract injury, intensive care admission, preterm birth, and rare maternal or neonatal death. Clear explanations allow informed consent and reduce unexpected decisions during an emergency.
Practical Priorities For A Safer Pathway
A reliable PAS program depends on repeatable processes. Imaging findings should be available to the operating team, referrals should occur early enough to allow consultation, and the hospital should rehearse the response to catastrophic obstetric hemorrhage. Documentation should make the plan understandable to every clinician who may encounter the patient.
Useful priorities include:
- Screen placental location and uterine-scar relationships during routine ultrasound.
- Refer suspected cases to an experienced maternal-fetal medicine or PAS service.
- Use structured ultrasound reporting and reserve MRI for specific anatomical or diagnostic questions.
- Assemble obstetric, anesthesia, transfusion, neonatal, radiology, and surgical expertise before delivery.
- Confirm blood availability, operating room readiness, postoperative monitoring, and emergency escalation procedures.
Simulation and multidisciplinary case review can identify weaknesses before they affect a patient. Teams may examine whether blood products can reach the operating room quickly, whether the chosen incision is documented, and whether communication remains clear during rapid deterioration. These practical details are as important as the imaging diagnosis itself.
Coordinating Care Before Delivery
Prenatal diagnosis of PAS is a process of risk estimation, anatomical mapping, and preparation. Ultrasound usually provides the initial assessment, MRI can clarify difficult or extensive disease, and clinical history determines how aggressively an uncertain finding should be managed. No scan can predict every operative event, so plans must include contingencies for hemorrhage, urinary tract involvement, premature delivery, and unexpected anatomy.
The safest pathway is usually created before labor begins, in a center with the personnel, blood resources, surgical capability, and neonatal support required for complex obstetric care. Patients benefit when the same information is shared across imaging, anesthesia, surgery, transfusion services, and neonatology.
Clinicians and institutions can use these principles to review their referral pathways, standardize reporting, and rehearse delivery scenarios for suspected PAS. Early coordination gives families clearer choices and gives the care team time to turn prenatal imaging into a carefully prepared operation.
