Another risk marker became apparent with widespread use of MSAFP and human chorionic gonadotropin (hCG) screening for neural-tube defects and aneuploidies. In one study of more than 9300 women screened at 14 to 22 weeks' gestation, the risk for accrete syndromes was eightfold higher with MSAFP levels >2.5 110M, and it was increased fourfold with maternal serum free �-hCG levels >2.5 MoM (Hung, 1999).
In cases offirst-and second-trimester accrete syndromes, there is usually hemorrhage that is the consequence ofcoexisting placenta previa. Such bleeding will typically prompt evaluation and management. In some women who do not have an associated previa, accreta may not be identiied until third-stage labor when an adhered placenta is encountered. Unfortunately, imaging modalities are less than perfect to identiy all of these placentas early.
Ideally, sonography is used for antepartum identiication of abnormal placental ingrowth (Chantraine, 2013; Jauniaux, 2016; Reddy, 2014; Tam Tam, 2012). Happe and colleagues (2018) found that first-trimester measurement of the smallest myometrial thickness can be used to predict the necessity for peripartum hysterectomy with an accrete syndrome. Other indings include loss of the normal hypoechoic retroplacental zone between the placenta and uterus, placental vascular lacunae, and placental bulging into the posterior bladder wall (Fig. 41-27). Using these criteria, Warshak and associates (2006) calculated the following values: sensitivity of 77 percent; specificity of 96 percent; positive-predictive creta shows mUltiple and massive placental "lakes" or "lacunae". (Reproduced with permission from Dr. Martha Rac in Cunningham FG: Placenta previa and morbidly adherent placenta. In Yeomans ER, Hofman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap's Operative Obstetrics, 3rd edition. New York, McGraw-Hili Education, 201o7b.) value of 98 percent. Similar values are cited by the American College ofObstetricians and Gynecologists (2017c) and others (Chalubinski, 2013; Elhawary, 2013; Maher, 2013).
Despite these findings, some investigators report less spectacular results with sonography aauniaux, 2016; Primo, 2014). Bowman and colleagues (2014)r.described the sensitivity of sonography to be 54 percent; specificity, 88 percent; positivepredictive value, 82 percent; negative-predictive value, 65 percent; and accuracy, 65 percent. Location afects sonographic accuracy. In one study, the detection rate was 90 percent for anterior placenta accreta compared with 50 percent for posterior wall ones (Pilloni, 2016). Nageotte (2014) concluded that identiication of the morbidly adherent placenta with sonography should be interpreted along with clinical and operative indings.