How do you diagnose placenta accreta (placenta accreta) versus other issues in a patient with suspected placenta previa and a history of two prior C-sections (cesarean sections)?

Diagnosing Placenta Accreta in a Patient with Placenta Previa and Two Prior Cesarean Sections

Ultrasound is the primary diagnostic tool for detecting placenta accreta spectrum, and your patient's combination of placenta previa with two prior cesarean sections places her at 40% risk for accreta—making accurate prenatal diagnosis critical to prevent catastrophic hemorrhage at delivery. 1

Understanding the High-Risk Context

Your patient has the "perfect storm" for placenta accreta spectrum:

• Placenta previa overlying a cesarean scar is the single most important risk factor, present in 49% of all accreta cases 2
• With two prior cesareans and current placenta previa, her risk jumps to 40% for developing accreta 1
• The risk escalates dramatically: 3% with previa alone, 11% with previa plus one cesarean, 40% with two cesareans, 61% with three, and 67% with five or more 1

How Ultrasound Identifies Placenta Accreta

Gray-scale ultrasound is both sensitive and specific enough to diagnose placenta accreta spectrum and should be the first-line imaging modality. 3, 4 The perinatologist looks for specific ultrasound features:

Key Ultrasound Findings for Accreta:

• Loss of the normal hypoechoic retroplacental zone (the clear space between placenta and uterine wall disappears) 1
• Thinning or disruption of the hyperechoic uterine serosa-bladder interface 1
• Presence of placental lacunae (irregular vascular spaces within the placenta that appear as "Swiss cheese" holes) 1
• Abnormal placental vascularity on color Doppler showing turbulent flow 1
• Bladder wall irregularity if invasion extends anteriorly 1

Important Caveat About Ultrasound Accuracy:

The absence of ultrasound findings does NOT rule out placenta accreta—clinical risk factors remain equally important as predictors. 1 Many ultrasound abnormalities associated with accreta can also appear in normal placentas, leading to both false positives and false negatives. 1 Interobserver variability is substantial, with sensitivities ranging from 53-74% and specificities from 71-95% even among experts. 1

When to Add MRI

MRI is not the preferred initial modality but may be helpful in specific situations: 1

• Posterior placenta previa (harder to visualize on ultrasound) 5
• Suspected placenta percreta (invasion through the uterine wall into bladder or other organs) 5, 6
• Ambiguous ultrasound findings requiring clarification 3

MRI does not clearly improve diagnostic accuracy beyond expert ultrasound alone for most cases. 1

Distinguishing Accreta from Other Issues

The perinatologist differentiates accreta from other conditions by:

What Accreta Is NOT:

• Not just placenta previa alone: Previa means abnormal location (covering the cervix), while accreta means abnormal invasion into the uterine wall 1
• Not placental abruption: Abruption shows placental separation with retroplacental hematoma, whereas accreta shows abnormal adherence 1
• Not uterine atony: This is a postpartum complication of uterine muscle tone, not placental invasion 1

The Pathophysiology That Explains the Imaging:

Accreta occurs because defects in the endometrial-myometrial interface at the cesarean scar prevent normal decidualization, allowing abnormally deep placental anchoring villi and trophoblast infiltration directly into the myometrium. 1 This is why the normal tissue planes disappear on ultrasound—the placenta literally invades where it shouldn't.

Critical Next Steps for Your Patient

This patient MUST deliver at a level III or IV maternal care facility with a multidisciplinary team experienced in managing placenta accreta spectrum. 1, 5, 2 This includes:

• Maternal-fetal medicine subspecialists 1
• Pelvic surgeons (gynecologic oncology or experienced OB surgeons) 5, 6
• Urologists (for potential bladder involvement) 5
• Interventional radiologists 5
• Obstetric anesthesiologists 5
• Blood bank with massive transfusion protocols 1, 5
• ICU capabilities 2

Planned delivery should occur at 34 0/7 to 35 6/7 weeks gestation to balance neonatal outcomes against maternal hemorrhage risk, as approximately 50% of women with accreta who wait beyond 36 weeks require emergent delivery for hemorrhage. 5, 2

The Surgical Reality

The standard approach is cesarean hysterectomy with the placenta left in situ—attempting to remove the placenta results in catastrophic hemorrhage and should be avoided. 1, 5, 2, 3 The placenta cannot separate normally because it's invaded into the uterine muscle, so trying to deliver it tears through vascular myometrium causing massive bleeding. 2

Preoperative Optimization:

• Maximize hemoglobin with oral or IV iron during pregnancy 5
• Notify blood bank in advance for large-volume transfusion preparation 5
• Consider ureteral stent placement if bladder involvement suspected 5
• Use transfusion ratios of 1:1:1 to 1:2:4 (packed RBCs:FFP:platelets) for hemorrhage 5

Common Pitfall to Avoid

The biggest mistake is failing to recognize the dramatically elevated risk in women with placenta previa AND prior cesarean deliveries, leading to delivery at an unprepared facility without adequate resources. 2 This patient's 40% accreta risk demands delivery at a specialized center—community hospitals are not equipped for the potential 3500+ mL blood loss and need for emergency hysterectomy that can occur. 7