Risk of Placenta Accreta After Myomectomy with Endometrial Cavity Entry
A. Increase - The risk of placenta accreta is definitively increased when the endometrial cavity is entered during myomectomy, as this creates a disruption of the endometrial-myometrial interface that damages the normal decidualization process and allows abnormally deep placental anchoring in future pregnancies. 1, 2
Pathophysiologic Mechanism
The American College of Obstetricians and Gynecologists explains that placenta accreta spectrum develops through a specific mechanism: defects in the endometrial-myometrial interface lead to failure of normal decidualization in areas of uterine scarring, which allows abnormally deep placental anchoring villi and trophoblast infiltration. 3, 1, 2
Entry into the endometrial cavity during myomectomy creates precisely this type of pathologic disruption. When the surgeon enters the endometrial cavity, this creates a full-thickness defect that damages the endometrial-myometrial interface and affects scar tissue development—the exact mechanism that increases placenta accreta likelihood. 1 This is particularly significant because it creates a defect similar to cesarean delivery rather than a subserosal defect that would not involve the decidual layer. 1
Established Risk Factor Status
Prior uterine surgeries, including myomectomy, are explicitly listed as established risk factors for placenta accreta spectrum by the American College of Obstetricians and Gynecologists. 1, 4 This places myomectomy in the same category as cesarean delivery, curettage, and Asherman syndrome as recognized causes of accreta. 1
Multiple case reports and series document placenta accreta occurring at myomectomy sites, particularly when the placenta overlies the surgical scar in subsequent pregnancies. 5, 6 One case series specifically documented placenta increta after hysteroscopic myomectomy, emphasizing that any uterine leiomyoma treatment carries increased risk for abnormal placentation. 6
Risk Magnitude and Clinical Context
The absolute magnitude of risk after myomectomy with cavity entry is not as precisely quantified as it is for cesarean delivery, where systematic data shows 3% baseline risk with placenta previa alone, escalating to 11% after one cesarean, 40% after three, and 67% after five or more cesarean deliveries. 3, 1 However, the pathophysiologic mechanism is identical. 1, 2, 7
The risk escalates dramatically if placenta previa develops overlying the myomectomy scar—similar to the well-established cesarean scar-previa combination that creates the highest accreta risk. 1 This represents the highest-risk scenario requiring intensive surveillance. 1
Clinical Implications for Future Pregnancies
Surveillance Requirements
- All future pregnancies require careful ultrasound evaluation for placenta location relative to the myomectomy scar site. 1, 5
- If the placenta overlies any uterine abnormality or surgical scar, a meticulous search for invasive placentation is warranted. 5
- Gray-scale ultrasound should assess for loss of the normal hypoechoic retroplacental zone, multiple placental lacunae, retroplacental myometrial thickness <1mm, and abnormalities of the uterine serosa-bladder interface. 1, 8
- Color Doppler imaging should evaluate for turbulent lacunar blood flow, increased subplacental vascularity, and vessels bridging the placenta to the uterine margin. 1, 8
Delivery Planning
- Women with suspected placenta accreta spectrum should be referred to a level III or IV maternal care facility with multidisciplinary expertise for delivery planning. 1, 8, 2
- Planned delivery at 34 0/7 to 35 6/7 weeks gestation optimizes outcomes in stable patients with confirmed accreta. 8
- The most accepted approach is cesarean hysterectomy with placenta left in situ, as attempts at placental removal are associated with significant hemorrhage risk. 2
Important Caveats
The absence of ultrasound findings does not preclude a diagnosis of placenta accreta spectrum—clinical risk factors (including history of myomectomy with cavity entry) remain equally important as predictors even when imaging appears normal. 2 This patient's surgical history alone mandates heightened vigilance regardless of imaging findings.