Assistant Professor of Radiology, Shahid Beheshti University of Medical Sciences
Consultant Radiologist in Tehran University of Medical Science (TUMS), Arash Hospital, Headmaster of Radiologic Department
There are three commonly recognized types abnormal adhered placenta defined by the depth of penetration of the placental villi into the myometrium.
The placenta accreta spectrum disorders include both abnormally adherent (accreta) and invasive placenta (increta and percreta).
Placenta accreta spectrum disorders prevent normal separation of the placenta at delivery, resulting in a high risk of severe post-partum hemorrhage.
Abnormally invasive placenta (increta and percreta) is a life-threatening condition, and a major cause of caesarean-hysterectomy and maternal morbidity and mortality.
The prevalence in the general population of pregnant women is around 1.7 per 10,000 pregnancies.
The incidence of PAS is 4.1% in women with one prior cesarean delivery and 13.3% in women with two or more previous caesarean deliveries.
Prenatal diagnosis of PAS is vital as it facilitates appropriate referral to a team experienced in the complexities such deliveries present and has been shown to reduce maternal morbidity.
In the FIGO consensus guidelines, there is a clinical grading system to categorize placental adherence at delivery,but the main criteria for diagnosis are sonographic signs.
Prenatal ultrasound diagnosis is based on a number of different signs. Standardized descriptions of these signs were proposed by the European Working Group on Abnormally Invasive Placenta (EW-AIP) which is going to explain with detail in the lecture.
There are two sub groups , 2D Grey-scale and Color Doppler imaging.
Magnetic Resonance Imaging is widely used to assist with the prenatal diagnosis of PAS, although the accuracy of MRI isn’t much more better than high resolution accurate sonography ;however, MRI is especially useful where evaluation of uteroplacental interface is difficult, for example when there is a posterior placenta.
Management depends both on the type of PAS and the standard practices of the specialist centre. Delivery is generally by planned caesarean section at around 34-36 weeks’ gestation, in order to avoid emergency delivery.
The two most common management strategies are caesarean-hysterectomy and leaving the placenta in situ (conservative management)