Table 1.

Clinical and histological grading system for PAS disorders (FIGO guidelines).

Grade	Definition
Clinical criteria		Histologic criteria
1. Abnormally adherent placenta (accreta)	At vaginal delivery: no separation with synthetic oxytocin and gentle controlled cord traction; attempts at manual removal of the placenta result in heavy bleeding from the placenta implantation site requiring mechanical or surgical procedures	Microscopic examination of the placental bed samples from the hysterectomy specimen shows extended areas of absent decidua between villous tissue and myometrium with placental villi attached directly to the superficial myometrium. The diagnosis cannot be made on just delivered placental tissue or on random biopsies of the placental bed
	If laparotomy is required (including for cesarean delivery): the same as above; macroscopically, the uterus shows no obvious distension over the placental bed (placental “bulge”), no placental tissue is seen invading through the surface of the uterus, and there is no or minimal neovascularity
2. Abnormally invasive placenta (increta)	At laparotomy: abnormal macroscopic findings over the placental bed: bluish/purple coloring and distension (placental “bulge”); significant amounts of hypervascularity (dense tangled bed of vessels or multiple vessels running parallel craniocaudally in the uterine serosa); no placental tissue seen to be invading through the uterine serosa; gentle cord traction results in the uterus being pulled inwards without separation of the placenta (so-called the dimple sign)	Hysterectomy specimen or partial myometrial resection of the increta area shows placental villi within the muscular fibers and sometimes in the lumen of the deep uterine vasculature (radial or arcuate arteries)
3. Abnormally invasive placenta (percreta)
3a. Limited to the uterine serosa	At laparotomy: abnormal macroscopic findings on the uterine serosal surface (as above) and placental tissue seen to be invading through the surface of the uterus; no invasion into any other organ, including the posterior wall of the bladder (a clear surgical plane can be identified between the bladder and uterus)	Hysterectomy specimen showing villous tissue within or breaching the uterine serosa
3b. With urinary bladder invasion	At laparotomy: placental villi are seen to be invading the bladder but no other organs: clear surgical plane cannot be identified between the bladder and uterus	Hysterectomy specimen showing villous tissue breaching the uterine serosa and invading the bladder wall tissue or urothelium
3c. With invasion of other pelvic tissue or organs	At laparotomy: placental villi are seen to be invading the broad ligament, vaginal wall, pelvic sidewall, or any other pelvic organ (with or without invasion of the bladder)	Hysterectomy specimen showing villous tissue breaching the uterine serosa and invading pelvic tissues/organs (with or without invasion of the bladder)

From Jauniaux et al. [38] with permission.