Why Placenta Accreta Spectrum is More Serious Than Placenta Previa
Placenta accreta spectrum is fundamentally more dangerous than placenta previa because it involves abnormal invasion of placental tissue into or through the uterine wall, creating a life-threatening hemorrhagic risk that typically requires hysterectomy, whereas placenta previa is simply an abnormal placental location that can be managed with cesarean delivery alone. 1
The Critical Difference in Pathophysiology
Placenta previa is a positional problem—the placenta covers the cervical opening but remains normally attached to the uterine wall and can separate appropriately after delivery. 2
Placenta accreta spectrum represents abnormal trophoblast invasion through defective decidua directly into the myometrium (accreta), deep into the myometrium (increta), or completely through the uterine wall into surrounding organs like the bladder (percreta). 1 This creates a vascular nightmare where the placenta cannot separate from the uterus after delivery without catastrophic hemorrhage. 1
Why the Hemorrhage Risk is Catastrophic
Severe PAS transforms the pelvis into an extremely high-flow vascular state with distorted anatomy that makes bleeding nearly impossible to control once it starts. 3
Attempts to remove the placenta are associated with significant hemorrhagic morbidity—this is why the standard approach is cesarean hysterectomy with the placenta left in place rather than trying to deliver it. 1, 4, 5
The bleeding can be massive and life-threatening, often requiring large-volume blood transfusions, intensive care unit admission, and emergency hysterectomy to save the mother's life. 1, 3
In contrast, placenta previa bleeding—while serious—can typically be managed with cesarean delivery and does not usually require hysterectomy unless accreta is also present. 2
The Devastating Surgical Reality
Even in experienced referral centers, cesarean hysterectomy for PAS results in prolonged surgery, frequent urinary tract injury, massive blood transfusion, and ICU admission. 3
Maternal morbidity and mortality rates are significantly elevated compared to placenta previa alone. 1
Postoperative complications include high rates of posttraumatic stress disorder, chronic pelvic pain, decreased quality of life, and depression. 3
Why Delivery at 34-35 Weeks is Recommended
The timing balances two competing risks: delivering too early (neonatal complications) versus waiting too long (catastrophic maternal hemorrhage). 4
The Evidence for Early Delivery
ACOG and FIGO recommend planned cesarean delivery at 34-38 weeks, with optimal timing at 34 0/7 to 35 6/7 weeks for stable patients. 1, 4
Approximately 50% of women with placenta accreta spectrum who wait beyond 36 weeks require emergent delivery for hemorrhage—this is the critical statistic that drives the recommendation. 4
The goal is to deliver before spontaneous labor or bleeding begins, because once hemorrhage starts in an uncontrolled setting, maternal mortality risk skyrockets. 1
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. 1, 4
Why Not Wait Longer?
The risk of spontaneous labor or bleeding increases dramatically with advancing gestational age, and emergency delivery in the setting of active hemorrhage has much worse outcomes than planned delivery. 4
Antenatal diagnosis allows for scheduled delivery in optimal conditions—this is the single most important factor in reducing maternal morbidity and mortality. 1, 5
The Compounding Risk When Both Conditions Coexist
Women with placenta previa AND prior cesarean deliveries have dramatically elevated risk for placenta accreta spectrum—the risk increases 7-fold after one cesarean to 56-fold after three cesareans. 1, 4
Placenta previa was present in 49% of placenta accreta spectrum cases in large cohort studies, making it the single most important risk factor. 1
This combination creates the perfect storm: abnormal placental location (previa) overlying a uterine scar where abnormal invasion (accreta) is most likely to occur. 1, 4
Common Pitfall to Avoid
Failure to diagnose placenta accreta spectrum in women with placenta previa and prior cesarean deliveries can lead to catastrophic hemorrhage. 4 All women with placenta previa and any prior uterine surgery must be evaluated with ultrasound for signs of accreta, and MRI should be considered in difficult cases. 1, 4