IMPACT OF PLACENTAL INVASION (PLACENTA ACCRETA SPECTRUM) ON PREGNANCY AND DELIVERY OUTCOMES IN WOMEN WITH UTERINE SCARS

Abstract

Placenta accreta spectrum (PAS) is a serious obstetric complication characterized by abnormal adherence of the placenta to the uterine myometrium. This condition has increased markedly among women with a history of prior cesarean section (uterine scar). PAS can lead to postpartum hemorrhage, hysterectomy, bladder injury and even maternal death. Therefore, understanding the etiology and pathogenesis of placen-ta invasion in women with a uterine scar is of great importance.[1,14,15]. Placenta accreta spectrum is a complex obstetric pathology associated with high maternal morbidity. This recently recognized disorder of placentation results from disruption of the endometrial-myometrial interface of the uterine wall. When first described about 80 years ago, it was mainly associated with manual removal of the placenta, curettage or post-endometritis changes. Superficial damage primarily leads to abnormally adherent placenta and is histologically diagnosed as partial or complete absence of the decidua.[2,13,16] Today, the principal cause of the placenta accreta spectrum is uterine surgery, in particular cesarean section scars that are secondary in nature. If re-epithelialization of the endometrium over the scar does not occur, trophoblast and chorionic tissues may invade the myometrium, including its vascular network, and may extend to the small pelvic organs. The trophoblastic cell changes observed in the placenta accreta spectrum are likely not a primary defect in trophoblast biology that causes excessive myometrial invasion, but rather secondary to an abnormal developing myometrial environment. Pathologists classify the placenta accreta spectrum into three categories: placenta accreta — chorionic villi attach to the myometrium without invading it; placenta increta — chorionic villi invade into the myometrium; and placenta percreta — chorionic villi penetrate through the full thickness of the myometrium. Over the past 35 years several prenatal ultrasound signs of the placenta accreta spectrum have been described, principally loss of the normal retroplacental clear zone (the hypoechoic zone), focal excessive thinning of the underlying myometrium, placental lacunae and placental vascular abnormalities (hypervascularity). The pathophysiological basis of these signs is related to persistent damage of the uterine wall down to the serosa, allowing placental tissue to reach deep uterine vasculature. Adherent and invasive placentation may coexist within the same placental bed and evolve with advancing pregnancy. This may explain why a single ultrasound sign or a fixed combination of signs is not specific enough to differentiate reliably the depth of abnormal placentation or to distinguish adherent from invasive placentation. Correlating pathological and clinical outcomes with prenatal imaging is important to improve screening, diagnosis and management of the placenta accreta spectrum, and standardized protocols should be developed.[3,10,11,12]