FIGURE 41-24 Morbidly adherent placentas: A. Placenta accreta. B. Placenta increta. C. Placenta percreta.
placenta accreta (Linn, 2015; Nliller, 2016). his implies an antecedent "constitutional endometrial defect" in most cases. The greater risk conveyed by previous surgical uterine trauma may be partially explained by an enhanced vulnerability to trophoblast invasion (Garmi, 2012; Gill, 2015; Jauniaux, 2017).
his association with prior trauma is reinforced by the close relationship between cesarean-scar pregnancy (CSP) and later development of placenta accreta in the same pregnancy. Indeed, accruing evidence suggests that CSP and accrete syndromes lie on a spectrum and that CSP is a precursor, as both share the same histopathology (Happe, 2018; Timor-Tritsch, 2014). CSP frequency has been reported to approximate 1 in 2000 pregnancies (Berhie, 2015; Rotas, 2006). Described in Chapter 19 (p. 381), early rupture and hemorrhage are not uncommon with CSP, and women often elect pregnancy-terminating interventions to avoid these (Michaels, 2015; Timor-Tritsch, 2015).
Variants of the morbidly adherent placenta are classified by the depth of trophoblastic growth (Figs. 41-24 and 41-25).
FIGURE 41-25 Varying degrees of myometrial invasion with the accrete syndromes. Incisions begin on the serosal surface and extend through to the placenta. A. In this case, the myometrium (M) shows minimal invasion by the placenta (P). S = uterine serosa. B. A greater degree of myometrial invasion is seen here. C. In this example, the placenta (backets) extends to the serosal edge, held by the surgeon's hand. No myometrium remains at this site. (Reproduced with permission from Dr. C. Edward Wells in Cunningham FG: Placenta previa and morbidly adherent placenta. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap's Operative Obstetrics, 3rd edition. New York, McGraw-Hili Education, 2017b.)
Placenta accreta indicates that villi are attached to the myome trium. With placenta in creta , villi actually invade the myome trium, and placenta percreta defines villi that penetrate through the myometrium and to or through the serosa (Bailit, 2015;
Silver, 20 15a). In clinical practice, these three variants are encountered in an approximate ratio of 80:15:5, respectively (Wong, 2008). In all three varieties, abnormal adherence may involve all lobules-total placenta accreta. If all or part of a single lobule is abnormally attached, it is described as a ocal placenta accreta. Histological diagnosis cannot be made from the placenta alone, and myometrial samples are necessary for confirmation (Benirschke, 2012) .