Why Placenta Accreta Spectrum Has Increased
The incidence of placenta accreta spectrum has risen dramatically—from 1 in 2,510 deliveries in the 1970s-1980s to 1 in 272 deliveries by 2016—directly paralleling the escalating cesarean delivery rate over the same four decades. 1
Primary Driver: Rising Cesarean Section Rates
The increased cesarean delivery rate is the single most important modifiable factor driving the placenta accreta epidemic. 1
Prior cesarean delivery creates uterine scarring that disrupts the endometrial-myometrial interface, preventing normal decidualization and allowing abnormally deep trophoblast invasion. 1
The risk escalates in a dose-dependent manner with each additional cesarean section:
In one Italian tertiary center, cesarean rates increased from 17% to 64% between the 1970s and 2000s, while placenta accreta incidence rose from 0.12% to 0.31% during the same period—prior cesarean section was the only risk factor showing a significant concomitant rise. 3
The Multiplicative Effect of Placenta Previa
When placenta previa overlies a cesarean scar, the risk of accreta spectrum increases exponentially. 1, 2
Placenta previa is present in >80% of all placenta accreta spectrum cases, making it the strongest ultrasonographic association. 1, 4
The combined risk of placenta previa plus prior cesarean creates a life-threatening scenario:
Placenta previa overlying a cesarean scar accounts for approximately 49% of all placenta accreta spectrum cases. 2, 4
Additional Contributing Factors
Beyond cesarean delivery, several other factors have contributed to the rising incidence. 1, 5
Uterine Surgery and Instrumentation
- Prior uterine surgeries (myomectomy with cavity entry, curettage) damage the endometrial-myometrial interface and increase accreta risk. 1, 2
- Dilation and curettage carries an odds ratio of approximately 2.8 for placenta accreta spectrum. 2
- Asherman syndrome (intrauterine adhesions) is an established independent risk factor. 1, 2
Demographic Shifts
- Advanced maternal age (≥35 years) independently raises the risk of placenta accreta spectrum. 1, 2, 6
- Multiparity is linked to higher incidence of the disorder. 1, 2
- Delayed childbearing in modern societies means more women are having pregnancies at advanced maternal age with accumulated uterine surgical history. 5
Assisted Reproductive Technology
Uterine Conservation Practices
- With increased conservative management of prior placenta accreta, previous retained placenta or placenta accreta have themselves become significant risk factors for recurrence. 5
Pathophysiologic Mechanism
The underlying mechanism explains why uterine scarring drives the epidemic. 1, 7
- Defects in the endometrial-myometrial interface (from cesarean scars, curettage, or other surgery) lead to failure of normal decidualization in the area of the scar. 1
- This allows abnormally deep placental anchoring villi and trophoblast infiltration into and through the myometrium. 1, 7
- Disruptions within the uterine cavity cause scar tissue development that affects the maternal-fetal interface, predisposing to morbid placentation. 1
Clinical Implications
Understanding this epidemiologic trend has critical practice implications. 1, 5
- Patients considering elective cesarean delivery should be counseled about the cumulative risk of placenta accreta spectrum in future pregnancies. 5
- Women with placenta previa and prior cesarean require targeted ultrasound evaluation for placenta accreta spectrum between 28-32 weeks gestation. 4
- Antenatal diagnosis and delivery planning at a Level III/IV maternal care center with multidisciplinary expertise dramatically improves maternal outcomes. 1, 4
- The absence of ultrasound findings does not exclude placenta accreta spectrum—clinical risk factors (placenta previa + prior cesarean) remain equally important predictors even when imaging appears normal. 1, 4