Placenta accreta spectrum

Placenta accreta spectrum (PAS) is a medical condition that occurs when all or part of the placenta attaches abnormally to the myometrium (the muscular layer of the uterine wall) during pregnancy. This condition was first documented in medical literature in 1927. Three grades of abnormal placental attachment are defined according to the depth of attachment and invasion into the muscular layers of the uterus. From least to most invasive uterine attachment they are: Placenta Accreta, Increta, and Percreta.

Because of abnormal attachment to the myometrium, PAS is associated with an increased risk of massive hemorrhaging, heavy bleeding, at the time of attempted vaginal delivery. This leads many to deliver through a caesarean section. The need for transfusion of blood products is frequent, and a surgical removal of the uterus (hysterectomy) is sometimes required to control life-threatening bleeding.

Rates of placenta accreta are increasing, and are even higher in developing countries. As of 2016, placenta accreta affects an estimated 1 in 272 pregnancies. Furthermore, the increase in PAS prevalence in recent decades has been a major cause of morbidity and mortality among pregnant women, and has been a main factor in the increase of caesarean deliveries.