Placenta accreta spectrum disorder (PAS) is a complication of pregnancy where the placenta attaches to the wall of the uterus (womb) in an abnormal way. The placenta is the organ that provides oxygen and nutrients to the developing fetus. Normally the placenta attaches quite superficially to the wall of uterus but, in PAS, the placenta adheres or invades in an abnormal way during the first trimester of pregnancy, pushing too deeply into the uterine wall (myometrium).
There are roughly three parts to the spectrum defined according to the depth the placenta invades into the myometrium:
PAS disorder occurs in around 1.7 per 10,000 pregnancies; the incidence increases with the presence of risk factors. Risk factors for PAS include: advanced maternal age, multiparity, previous uterine surgery including curettage, assisted reproductive techniques and previous caesarean delivery.
The most commonly described risk factor is the association of previous caesarean delivery and low-lying placenta or placenta previa.
In case of suspicion of PAS, you will be referred to a center with expertise for prenatal diagnosis of PAS. The prenatal diagnosis consists of an ultrasound, performed especially for the evaluation of the uteroplacental interface, the area where the placenta attaches to the uterine wall. This ultrasound should be performed with full bladder and, in some cases, magnetic resonance imaging can also be used.
This abnormal adherence of the placenta prevents the normal separation of the placenta at the time of delivery and is at high risk of severe post-partum hemorrhage. In some cases, especially with partial placenta accreta, there may be no clinical consequence at delivery.
Management of PAS disorders may differ depending on your specialist center and the degree of invasiveness of the placenta. Some centers perform a caesarean-hysterectomy, where the uterus (womb) is removed during a cesarean delivery of the baby. Other centers use conservative management, where the placenta is left in the uterus until its complete reabsorption. The best management is the one you decide with your expert center. Generally, the management of PAS consists of a planned caesarean delivery under general anesthesia.
PAS disorders do not usually affect the fetus if placental function is preserved. The possible consequences for your baby are related to moderate prematurity, if caesarean delivery is performed before term, and the risks of general anesthesia. In many cases, delivery will be planned for 35 weeks’ gestational age. In some cases, delivery may need to take place earlier.
The recurrent risk for a future pregnancy is around 22% to 29% if uterus was conserved.
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Last updated September 2019