What is the management approach for a pregnancy with a very thin or nearly absent myometrial (muscle layer of the uterus) layer between the placenta and bladder or serosa on imaging, indicating potential placenta accreta spectrum disorder?

Management of Very Thin or Nearly Absent Myometrial Layer Between Placenta and Bladder/Serosa

This imaging finding is highly suggestive of placenta accreta spectrum disorder (PASD) and mandates immediate referral to a tertiary care center with multidisciplinary expertise, planned cesarean hysterectomy at 34-36 weeks gestation, and avoidance of any attempt at placental removal to prevent catastrophic hemorrhage. 1, 2

Diagnostic Confirmation and Staging

Myometrial thickness <1 mm is a specific diagnostic marker for PASD that should not be interpreted in isolation. 1

Complete the diagnostic workup:

• Add Doppler ultrasound immediately to assess for increased placental vascular flow, subplacental hypervascularity, and bridging vessels from placenta to bladder, which have 97% sensitivity and 92% specificity when "numerous coherent vessels" are present 1

• Look for additional ultrasound markers including intraplacental lacunae (multiple, large, irregular), loss of retroplacental clear zone, placental bulging into bladder, and bladder wall interruption—the presence of 3 or more markers increases sensitivity to 84.6% and specificity to 92.3% 1, 3

• Obtain MRI without contrast after 24 weeks (ideally 30-35 weeks) if ultrasound findings are equivocal or to define extent of invasion for surgical planning, particularly for posterior placentation or suspected percreta 1

• MRI should assess for dark T2 intraplacental bands (77-88% sensitivity), focal myometrial interruption, bladder wall invasion, and parametrial involvement—3 or more MRI signs have 92.3% sensitivity 1, 3

Immediate Management Steps

Referral and team assembly:

Transfer care immediately to a level III or IV maternal care facility with maternal-fetal medicine subspecialists, experienced pelvic surgeons, urologists, interventional radiologists, obstetric anesthesiologists, neonatologists, and blood bank capable of massive transfusion protocols 4, 2

Optimize maternal status:

• Maximize hemoglobin during pregnancy with oral or intravenous iron supplementation to treat any anemia 4

• Notify blood bank early and ensure availability of large-volume blood products with established massive transfusion protocols 4, 2

Surveillance protocol:

• Perform follow-up ultrasound at 28-32 weeks to assess for progression of invasion depth, placental edge location, and cervical length 1, 5

• Weekly or biweekly cervical length measurements in third trimester to predict antepartum bleeding risk 1

Delivery Planning

Timing:

Schedule planned cesarean delivery at 34 0/7 to 35 6/7 weeks gestation to balance neonatal outcomes against maternal hemorrhage risk—do not delay beyond 36 weeks as approximately 50% require emergent delivery for hemorrhage after this point 4, 2

• Administer antenatal corticosteroids when delivery is anticipated before 37 weeks 4

• Have contingency plan for emergent delivery as bleeding risk increases with advancing gestational age 4

Surgical approach:

The most accepted approach is cesarean hysterectomy with placenta left in situ—attempts at placental removal are associated with catastrophic hemorrhage and should be avoided 4, 2, 6

Preoperative preparation:

• Consider ureteral stent placement if bladder involvement is suspected based on imaging 4

• Coordinate dorsal lithotomy positioning to allow vaginal access and optimal surgical visualization 4

• Inspect uterus after peritoneal entry to determine placental location and optimize uterine incision away from placenta when possible 4

Intraoperative Management

Hemorrhage control:

• Transfuse packed red blood cells, fresh frozen plasma, and platelets in 1:1:1 fixed ratio when acute hemorrhage occurs 4

• Maintain patient temperature >36°C as clotting factors function poorly at lower temperatures 4

• Re-dose prophylactic antibiotics if blood loss exceeds 1,500 mL 4

Laboratory monitoring:

Obtain baseline platelet count, PT, PTT, and fibrinogen at initiation of bleeding and monitor serially 4

Critical Pitfalls to Avoid

• Never perform digital pelvic examination until placenta previa has been excluded, as this can trigger massive hemorrhage 5, 4

• Never attempt forced placental removal when abnormal adherence is encountered—this causes profuse hemorrhage 4, 6

• Do not rely on absence of ultrasound findings to exclude PASD—clinical risk factors (prior cesarean delivery, placenta previa, advanced maternal age) remain equally important predictors 7, 2

• Do not interpret single imaging sign in isolation—myometrial thinning alone has limited specificity and must be considered with other markers 1

Alternative Conservative Management

Leaving placenta in situ without hysterectomy may be considered in highly selected patients desiring fertility preservation, but this requires extensive counseling about risks including delayed hemorrhage (median 5 weeks postpartum), infection, coagulopathy, and need for delayed hysterectomy in 45% of cases 6

• This approach involves no attempt at placental removal, hysterotomy closure, prophylactic IV antibiotics for up to 1 week, and close outpatient follow-up until uterus is empty (median 18 weeks) 6

• This conservative approach should only be attempted at experienced centers with immediate access to surgical intervention 6