Risk of Placenta Accreta After Myomectomy with Endometrial Cavity Entry
A. Increase - The risk of placenta accreta is increased when the endometrial cavity is entered during myomectomy, as this creates a full-thickness uterine defect that disrupts the endometrial-myometrial interface, establishing the pathophysiologic foundation for abnormal placental invasion in future pregnancies.
Mechanism of Increased Risk
The American College of Obstetricians and Gynecologists explains that placenta accreta spectrum develops when defects in the endometrial-myometrial interface lead to failure of normal decidualization in areas of uterine scarring, allowing abnormally deep placental anchoring and trophoblast infiltration 1.
Entry into the endometrial cavity during myomectomy is particularly significant because:
- It creates a full-thickness defect similar to cesarean delivery, rather than a subserosal defect that would not involve the decidual layer 1
- This disruption within the uterine cavity damages the endometrial-myometrial interface, affecting scar tissue development and increasing the likelihood of placenta accreta 1
- The defect allows abnormal trophoblast invasion through defective decidua directly into the myometrium 2
Evidence Supporting Increased Risk
Prior uterine surgeries are explicitly listed as established risk factors for placenta accreta spectrum by the American College of Obstetricians and Gynecologists, alongside cesarean delivery, curettage, and Asherman syndrome 1. Multiple case reports and series confirm placenta accreta occurring at myomectomy sites 3, 4.
Previous myomectomy is recognized as a risk factor for abnormal placentation in the literature 5, and patients with a history of hysteroscopic myomectomy or other uterine leiomyoma treatment are at increased risk for abnormal placentation 4.
Critical Caveat: The Placenta Previa Factor
If placenta previa develops overlying the myomectomy scar, the risk escalates dramatically:
- Similar to the well-established cesarean scar-previa combination that creates 11-67% accreta risk depending on the number of prior surgeries 1
- When the placenta overlies any uterine abnormality, a careful search for invasive placentation is warranted 3
- The combination of placenta previa and prior cesarean deliveries creates risk increasing from 11% with one cesarean to 67% with five or more 6
Quantifying the Absolute Risk
An important nuance: While one study found 0% placenta accreta in women with prior myomectomy (95% CI 0-1.98%) 7, this study likely included predominantly subserosal myomectomies where the endometrial cavity was NOT entered. The absolute magnitude of increased risk after myomectomy with endometrial cavity entry is not as precisely quantified as it is for cesarean delivery 1.
Recent evidence demonstrates that endometrial defects detected after uterine surgery are associated with 100% incidence of PAS when pregnancy occurs before endometrial restoration, compared to 20% when endometrial restoration occurs 8.
Clinical Implications for Future Pregnancies
Imaging surveillance is essential:
- Gray-scale ultrasound should be the first-line imaging modality, looking for loss of the normal hypoechoic retroplacental zone, placental lacunae, thinning of the uterine serosa-bladder interface, and abnormal placental vascularity 1, 6
- Imaging studies are suggested in patients with history of myomectomy to coordinate multidisciplinary care 4
If placenta accreta spectrum is diagnosed: