What is Placenta Accreta?
Placenta accreta is abnormal trophoblast invasion of part or all of the placenta into the myometrium of the uterine wall, representing a spectrum of pathologic placental adherence that includes placenta accreta (adherence to myometrium), placenta increta (invasion into myometrium), and placenta percreta (invasion through the uterine wall into surrounding organs). 1
Pathophysiology
The underlying mechanism involves a defect at the endometrial/myometrial interface that leads to failure of normal decidualization in areas of uterine scarring, which allows abnormally deep placental anchoring villi and trophoblast infiltration. 1 This creates a vascular nightmare where the placenta cannot separate from the uterus after delivery without catastrophic hemorrhage. 2
Clinical Significance and Mortality Risk
- Placenta accreta spectrum is one of the most dangerous conditions in pregnancy, with severe and sometimes life-threatening hemorrhage being the primary threat to maternal survival. 3
- Maternal mortality rates are increased for women with this condition, and patients are more likely to require hysterectomy at delivery or during the postpartum period with longer hospital stays. 1
- The condition transforms the pelvis into an extremely high-flow vascular state that distorts the uterus and surrounding anatomy. 3
Epidemiology and Rising Incidence
- The incidence has increased dramatically from 1 in 2,510-4,017 in the 1970s-1980s to 1 in 272 birth-related hospital discharges in the United States by 2016. 1
- This rising rate directly parallels the increasing cesarean delivery rate over the past four decades. 1
Major Risk Factors
The single most important risk factor is placenta previa overlying a cesarean scar, which is present in 49% of all accreta cases. 4
- Prior cesarean delivery is the most common risk factor, with risk escalating dramatically with each additional cesarean: 0.3% with one prior cesarean, increasing to 6.74% with five or more cesarean deliveries. 1
- When placenta previa and prior cesareans combine, the risk becomes exponential: 3% with previa alone, 11% with previa plus one cesarean, 40% with two cesareans, 61% with three cesareans, and 67% with five or more cesareans. 4
- Additional risk factors include advanced maternal age, multiparity, prior uterine surgeries or curettage, Asherman syndrome, IVF, short intervals between cesareans, and smoking. 1, 5
Critical Management Principle
Attempts at placental removal are associated with catastrophic hemorrhage and must be avoided—the standard approach is cesarean hysterectomy with the placenta left in situ after fetal delivery. 1, 6 This is not a condition where conservative management should be attempted outside of carefully selected research settings, as it carries a 28.6% recurrence risk in subsequent pregnancies. 6