Placenta Percreta: Evidence‑Based Risk Factors and Pathophysiology

Primary Risk Factors

Prior cesarean delivery markedly increases the risk of placenta percreta, rising from ≈0.3 % after one cesarean to ≈6.7 % after five or more cesareans【1】【2】.
When placenta previa co‑exists with prior cesarean delivery, the risk escalates dramatically: 3 % with no cesarean, 11 % with one, 40 % with two, 61 % with three, and ≈67 % with five or more cesareans【1】【2】.

Advanced maternal age is an independent risk factor for placenta percreta【1】【2】.
Multiparity (having given birth multiple times) raises risk independent of cesarean history【1】【2】.
Prior uterine surgeries or curettage damage the endometrial‑myometrial interface, increasing susceptibility【1】【2】.
Asherman syndrome (intra‑uterine adhesions) is a recognized risk factor【1】【2】.

Placenta percreta can occur in nulliparous women with unscarred uteri, demonstrating that mechanisms beyond uterine scarring can contribute【2】.

The leading hypothesis attributes placenta percreta to defects in the endometrial‑myometrial interface caused by uterine scarring, leading to failure of normal decidualization and permitting abnormally deep placental villi and trophoblast infiltration【1】【2】.

In placenta percreta, placental villi penetrate completely through the myometrium to the uterine serosa and may involve adjacent organs such as the bladder, cervix, or parametrial tissue【3】.
Disruptions within the uterine cavity create focal areas of decidual deficiency, facilitating invasive growth of trophoblast tissue【1】【2】.
The placenta adheres directly to myometrial smooth‑muscle fibers without intervening decidua, making separation impossible without catastrophic hemorrhage【4】.

Pathologic examination reveals decidual deficiency with increased extravillous trophoblast at sites of abnormal invasion【4】.
In delivered placentas, basal‑plate myometrial fibers may be present, confirming focal adherence and the absence of a normal decidual separation zone【4】.

The American College of Obstetricians and Gynecologists recommends understanding that placenta accreta spectrum represents abnormal trophoblast invasion through defective decidua directly into the myometrium, deep into the myometrium, or completely through the uterine wall into surrounding organs, creating a vascular nightmare where the placenta cannot separate from the uterus after delivery without catastrophic hemorrhage 5, 6
Placenta accreta spectrum is associated with a high risk of hemorrhagic morbidity, and attempts to remove the placenta are associated with significant hemorrhagic morbidity, which is why the standard approach is cesarean hysterectomy with the placenta left in place rather than trying to deliver it 5, 7

The American College of Radiology recommends planned cesarean delivery at 34-38 weeks, with optimal timing at 34 0/7 to 35 6/7 weeks for stable patients with placenta accreta spectrum 6, 7
Approximately 50% of women with placenta accreta spectrum who wait beyond 36 weeks require emergent delivery for hemorrhage, which drives the recommendation for early delivery 7
Delivery must occur at a level III or IV maternal care facility with a multidisciplinary team, including maternal-fetal medicine, pelvic surgeons, urologists, interventional radiologists, obstetric anesthesiologists, blood bank with massive transfusion protocols, and ICU capabilities 5, 7

Women with placenta previa AND prior cesarean deliveries have dramatically elevated risk for placenta accreta spectrum, with the risk increasing 7-fold after one cesarean to 56-fold after three cesareans 6, 7
Placenta previa was present in 49% of placenta accreta spectrum cases in large cohort studies, making it the single most important risk factor 6
The combination of placenta previa and prior cesarean deliveries creates the perfect storm: abnormal placental location overlying a uterine scar where abnormal invasion is most likely to occur 6, 7