Risk of Placenta Accreta After Myomectomy with Endometrial Cavity Entry
Your patient faces an increased risk of placenta accreta spectrum in future pregnancies due to the endometrial cavity entry during myomectomy, and this risk will escalate dramatically if placenta previa develops overlying the myomectomy scar. 1
Understanding Why This Creates Risk
The American College of Obstetricians and Gynecologists identifies prior uterine surgeries—including myomectomy—as established risk factors for placenta accreta spectrum, alongside cesarean delivery, curettage, and Asherman syndrome 2, 1
Entry into the endometrial cavity is particularly concerning because it creates a full-thickness defect in the endometrial-myometrial interface, similar to cesarean delivery, rather than a subserosal defect that would spare the decidual layer 1
This disruption damages the endometrial-myometrial interface where normal decidualization should occur, allowing abnormally deep placental anchoring and trophoblast infiltration in areas of uterine scarring 2, 1
Quantifying the Risk
While the absolute magnitude of increased risk after myomectomy is not as precisely quantified as it is for cesarean delivery (where risk ranges from 0.3% after one cesarean to 6.74% after five cesareans), the mechanism of injury is comparable when the endometrial cavity is entered 1
The critical scenario to monitor for is placenta previa overlying the myomectomy scar—this combination creates the same "perfect storm" seen with cesarean scars, where abnormal placental location overlies damaged uterine tissue 1, 3
If placenta previa develops over the myomectomy scar, expect risk levels similar to the cesarean-previa combination: 11% with one prior surgery, escalating to 40-67% with multiple surgeries 2, 1
Clinical Evidence Supporting This Risk
Case reports document placenta accreta occurring at myomectomy sites, particularly when the placenta overlies uterine abnormalities or surgical scars 4
A retrospective cohort study of 367 women with prior myomectomy undergoing cesarean delivery found significantly increased rates of cesarean hysterectomy (1.4% vs 0.2%, adjusted OR 3.43) and transfusion requirements compared to controls 5
Hysteroscopic myomectomy cases have resulted in placenta increta, demonstrating that even minimally invasive approaches that enter the endometrial cavity create accreta risk 6
Surveillance Strategy for Future Pregnancies
Obtain early ultrasound at 18-20 weeks to identify placental location relative to the myomectomy scar 1, 7
If the placenta is not overlying the scar, the risk remains elevated but substantially lower than the previa-scar combination 1
Gray-scale ultrasound should be your first-line imaging modality, specifically looking for: loss of the normal hypoechoic retroplacental zone, placental lacunae, thinning of the uterine serosa-bladder interface (<1mm), and abnormal placental vascularity 1, 7
If ultrasound findings are equivocal and clinical suspicion remains high, MRI can provide additional diagnostic information 8, 6
Critical Caveat About Negative Imaging
The absence of ultrasound findings does not rule out placenta accreta—clinical risk factors (like your patient's endometrial cavity entry during myomectomy) remain equally important predictors 7
Interobserver variability in ultrasound interpretation is substantial, so maintain high clinical suspicion regardless of initial imaging reports 7
Delivery Planning If Accreta Is Suspected
Delivery must occur at a level III or IV maternal care facility with multidisciplinary capabilities, including maternal-fetal medicine, pelvic surgeons, urologists, interventional radiologists, obstetric anesthesiologists, and blood bank with massive transfusion protocols 2, 7, 3
Planned cesarean 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 7, 3
The standard surgical approach is cesarean hysterectomy with the placenta left in situ—attempting placental removal results in catastrophic hemorrhage and should be avoided 7, 3, 8