he frequency of accrete syndromes was 1 in 20,000 births almost 100 years ago (McKeogh, 1951). As late as 1971, Hell man and Pritchard in the 14th edition of Williams Obstetrics described accreta to be the subject of case reports. Since then, the incidence has grown remarkably in direct relationship to the rising cesarean delivery rate. For example, incidence was 1 in 2500 births in the 1980s, but it was 1 per 731 births in the report from the MFMU Network comprising 115,502 women (Bailit, 2015). And a Canadian study of more than 570,000 births found an incidence of 1 in 700 deliveries (Mehrabadi, 2015). In the Nationwide Inpatient Sample, the prevalence of accreta was 3.7 per 1000 births-1 per 270 (Mogos, 2016).
This rising frequency has made accrete syndromes one of the most formidable problems in obstetrics. In one review of 5367 pregnancy-related maternal deaths in the United States from 2006 to 2013, 13 percent were due to hemorrhage caused by accrete syndromes (Creanga, 2015, 2017). In addition, they are a leading cause of hemorrhage and emergency peripartum hysterectomy (Awan, 2011; Eller, 2011; Rossi, 2010). The American College of Obstetricians and Gynecologists (2017 c) and the Society for Maternal-Fetal Medicine (2010) have taken the lead to address and optimize management.
In subsequent pregnancies following placenta accreta, recurrence risks are high. Women in whom hysterectomy is avoided have an estimated 20-percent incidence of recurrence (Cunningham, 2016; Roeca, 2017). In addition, some evidence shows that these women have greater risks for previa, uterine rupture, and hysterectomy (Eshkoli, 2013).
hese are similar in many aspects to those for placenta previa (p. 774). That said, the two most important risk factors are an associated previa, a prior cesarean delivery, and more likely a combination of the two (Kia', 2014). A classical hysterotomy incision has a higher risk for a subsequent accrete placenta (Gyami-Bannerman, 2012). In fact, almost half of women with a prior cesarean delivery had myometrial fibers seen microscopically adhered to the placenta (Hardardottir, 1996; Miller, 2016). An associated previa confers an even higher risk. his is shown in Figure 41-26, and the astonishing increase in frequency of associated accrete syndromes is apparent with a concomitant previa.
FIGURE 41-26 Frequency of morbidly adherent placenta in women with 1 to 5 prior cesarean deliveries (CDs) now with a previa. (Data from Silver, 2006.)
Dysfunctional decidual formation also may follow any other type of myometrial trauma such as curettage or endometrial ablation (Benirschke, 2012; Gill, 2015). Even without a prior hysterotomy, coexisting placenta previa is additive to frequency, and in one study, 10 percent ofsuch women with a previa had an associated accrete syndrome. A shorter cervical length with placenta accrete syndromes did not confer a greater risk for preterm delivery (Rae, 2017).