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Normally, the placenta attaches to the inner lining of the uterus and separates from the uterine wall after your baby is delivered. Placenta accreta spectrum (PAS) occurs when the placenta attaches abnormally firmly or grows too deeply into the wall of the uterus. This can make it difficult or unsafe for the placenta to separate normally after delivery.
Placenta accreta spectrum varies in severity depending on how deeply the placenta is attached. If PAS is suspected during pregnancy, additional imaging and specialized delivery planning are usually recommended.
Types of Placenta Accreta Spectrum
Types of Placenta Accreta Spectrum
Placenta accreta spectrum describes a range of abnormal placental attachment. The different terms describe how deeply the placenta has grown into or through the wall of the uterus:
Placenta accreta: The placenta attaches too firmly to the uterine wall but does not grow deeply into the uterine muscle.
Placenta increta: The placenta grows into the muscular wall of the uterus.
Placenta percreta: The placenta grows through the uterine wall and may extend into nearby structures, most commonly the bladder.
These conditions are now collectively referred to as placenta accreta spectrum (PAS) because the depth of attachment can vary and may not always be known with certainty before delivery.
Risk Factors for Placenta Accreta Spectrum
Risk Factors for Placenta Accreta Spectrum
PAS is more likely when there is an area of scarring in the uterus where the placenta implants. The risk is particularly increased when placenta previa or a low-lying placenta occurs in someone who has had a previous cesarean delivery. Other risk factors include prior uterine surgery or procedures, prior placenta accreta spectrum, and increasing maternal age.
Why Does Placenta Accreta Matter?
Why Does Placenta Accreta Matter?
The main concern with PAS is that the placenta may not separate normally after delivery. Attempting to remove an abnormally adherent placenta can cause severe bleeding (hemorrhage) and may require blood transfusion or other treatments to control bleeding. Depending on how deeply the placenta is attached, surrounding structures such as the bladder may also be involved.
Planning for Delivery
Planning for Delivery
When PAS is strongly suspected, delivery is typically planned in advance at a hospital with an experienced multidisciplinary team and resources to manage significant bleeding.
For many patients with PAS, the safest approach is a planned cesarean hysterectomy, in which the baby is delivered by C-section and the uterus is then removed with the placenta left in place rather than attempting to separate it from the uterine wall.
Your specific delivery plan will depend on the location and severity of the placental attachment, your medical and surgical history, and the resources available at your delivery hospital.
If you have placenta previa or suspected PAS, vaginal bleeding should be evaluated promptly. Your care team will provide specific instructions about when and where to seek care.
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