**2. The prenatal prediction of placenta accreta in women with placenta previa**

#### **2.1. Ultrasonography**

It has been reported that ultrasonography is the most useful method for diagnosing placenta accreta. Previous studies have demonstrated that ultrasound (US) findings involving the presence of placental lacunae (PL) [4], an anterior myometrial thickening [5], loss of the retroplacental hypoechoic clear zone (LCZ) [6], anomalies of the bladder-myometrium interface [7], and the presence of turbulent blood flow (TBF) in the arteries radiating from the placenta toward the uterine serosa, detected by color Doppler [8] are associated with placenta accreta. However, these previous results were based on retrospective studies for pregnant women with and without placenta previa.

**2.2. Magnetic resonance imaging**

internal uterine os [11].

stillbirth or neonatal death [18].

**2.3. Diagnostic scoring systems**

the prospective study (OR, 24.6; 95% CI, 4.7–129.2; p < 0.01) [9].

Some investigators suggested that MRI was a useful tool for diagnosing placenta accreta prenatally [12, 13]. MRI findings suggestive of placenta accreta included indistinctness or the absence of myometrial wall at the placental site, loss of the thin T2 dark uteroplacental interface, a nodular interface between the placenta and the uterus, a mass effect of the placenta on the uterus causing uterine outer bulge, heterogeneous signal intensity within the placenta, dark intraplacental bands on T2-weighted images, and abnormal dilated venous lakes within the placenta [13–15]. MRI provided advantages in diagnosing placenta accreta in women who had posterior placental location [16]. We found that MRI was selected as a significant finding in predicting placenta accreta in pregnant women with placenta previa by univariate analyses in

**Figure 1.** (A) The presence of the irregular sign in a case with placenta accreta. (B) The absence of the irregular sign in a case without placenta accreta. Dashed white marks indicate the border between the placenta and myometrium around

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However, other investigators claimed that MRI was more expensive and invasive examination than US; therefore, US should be the diagnostic modality of first choice for placenta accreta, and MRI was not always necessary [17]. Dynamic contrast-enhanced MRI with gadolinium (Gd) is not recommended at any time during pregnancy, because the use of Gd increases the risk of a broad set of rheumatological, inflammatory, or infiltrative skin conditions and of

Diagnostic scoring systems may be more useful than a single US finding for predicting placenta accreta in women with a history of previous CS, placenta previa, or low-lying placenta [19–21]. These scoring systems include several US findings suggestive of placenta accreta, the presence of placenta previa, and the number of prior CS. Optimal cut-off values of these scores determined in the retrospective or prospective studies yielded 72.0–94.2% sensitivity, 52.5–85.0% specificity, 63.4–70.0% PPV, and 86.0–100% NPV for the prediction of placenta accreta [19–21].

In the prospective study, we aimed to determine more effective imaging for predicting placenta accreta in women with placenta previa using stepwise logistic regression analyses [9]. Univariate logistic regression analyses demonstrated that US findings of anterior placental location (odds ratio [OR], 5.1; 95% confidence interval [CI], 1.2–20.5; p < 0.05), grade 2 or higher PL (PL ≥ G2) (OR, 17.0; 95%CI, 4.0–71.1; p < 0. 01), LCZ (OR, 49.4; 95% CI, 8.5–2862; p < 0.01), and magnetic resonance imaging (MRI) (OR, 24.6; 95% CI, 4.7–129.2; p < 0.01) were associated with placenta accreta. Multivariable analyses revealed that LCZ (OR, 15.6; 95%CI, 2.1–114.6; p < 0.01) was a single significant predictor of placenta accreta in women with placenta previa [9]. In this study, LCZ yielded 86.7% sensitivity, 88.4% specificity, 72.2% positive predictive value (PPV), and 95.0% negative predictive value (NPV) for the prediction of placenta accreta in women with placenta previa. In contrast, a previous study found that LCZ had low PPV for predicting placenta accreta, because LCZ is often observed among women with anterior placental location during normal pregnancy [10]. However, the previous study enrolled women who had anterior placental location and a history of cesarean section (CS); if the subjects were limited to women with placenta previa, diagnostic accuracy of LCZ might be improved.

Recently, we demonstrated that a novel US finding referred to as an "irregular sign" might be useful for predicting placenta accreta in women with placenta previa [11]. The irregular sign is defined as the irregularity of the border between the placenta and the myometrium around internal uterine os observed by transvaginal ultrasonography (**Figure 1**). The presence of irregular sign yielded 56.5% sensitivity, 99.3% specificity, 92.9% PPV, and 93.8% NPV for predicting placenta accreta in women with placenta previa [11].

**Figure 1.** (A) The presence of the irregular sign in a case with placenta accreta. (B) The absence of the irregular sign in a case without placenta accreta. Dashed white marks indicate the border between the placenta and myometrium around internal uterine os [11].

#### **2.2. Magnetic resonance imaging**

including obstetric anesthesia, appropriate surgical expertise, available blood products, and interventional radiology for uterine artery embolization [2, 3]. Therefore, accurate prenatal

This review will focus on the recent knowledge regarding the prenatal diagnosis and manage-

It has been reported that ultrasonography is the most useful method for diagnosing placenta accreta. Previous studies have demonstrated that ultrasound (US) findings involving the presence of placental lacunae (PL) [4], an anterior myometrial thickening [5], loss of the retroplacental hypoechoic clear zone (LCZ) [6], anomalies of the bladder-myometrium interface [7], and the presence of turbulent blood flow (TBF) in the arteries radiating from the placenta toward the uterine serosa, detected by color Doppler [8] are associated with placenta accreta. However, these previous results were based on retrospective studies for pregnant women

In the prospective study, we aimed to determine more effective imaging for predicting placenta accreta in women with placenta previa using stepwise logistic regression analyses [9]. Univariate logistic regression analyses demonstrated that US findings of anterior placental location (odds ratio [OR], 5.1; 95% confidence interval [CI], 1.2–20.5; p < 0.05), grade 2 or higher PL (PL ≥ G2) (OR, 17.0; 95%CI, 4.0–71.1; p < 0. 01), LCZ (OR, 49.4; 95% CI, 8.5–2862; p < 0.01), and magnetic resonance imaging (MRI) (OR, 24.6; 95% CI, 4.7–129.2; p < 0.01) were associated with placenta accreta. Multivariable analyses revealed that LCZ (OR, 15.6; 95%CI, 2.1–114.6; p < 0.01) was a single significant predictor of placenta accreta in women with placenta previa [9]. In this study, LCZ yielded 86.7% sensitivity, 88.4% specificity, 72.2% positive predictive value (PPV), and 95.0% negative predictive value (NPV) for the prediction of placenta accreta in women with placenta previa. In contrast, a previous study found that LCZ had low PPV for predicting placenta accreta, because LCZ is often observed among women with anterior placental location during normal pregnancy [10]. However, the previous study enrolled women who had anterior placental location and a history of cesarean section (CS); if the subjects were limited to women with placenta previa, diagnostic accuracy of LCZ might

Recently, we demonstrated that a novel US finding referred to as an "irregular sign" might be useful for predicting placenta accreta in women with placenta previa [11]. The irregular sign is defined as the irregularity of the border between the placenta and the myometrium around internal uterine os observed by transvaginal ultrasonography (**Figure 1**). The presence of irregular sign yielded 56.5% sensitivity, 99.3% specificity, 92.9% PPV, and 93.8% NPV

for predicting placenta accreta in women with placenta previa [11].

prediction of placenta accreta in women with placenta previa is important.

**2. The prenatal prediction of placenta accreta in women with** 

ment of placenta accreta in women with placenta previa.

**placenta previa**

86 Placenta

**2.1. Ultrasonography**

be improved.

with and without placenta previa.

Some investigators suggested that MRI was a useful tool for diagnosing placenta accreta prenatally [12, 13]. MRI findings suggestive of placenta accreta included indistinctness or the absence of myometrial wall at the placental site, loss of the thin T2 dark uteroplacental interface, a nodular interface between the placenta and the uterus, a mass effect of the placenta on the uterus causing uterine outer bulge, heterogeneous signal intensity within the placenta, dark intraplacental bands on T2-weighted images, and abnormal dilated venous lakes within the placenta [13–15]. MRI provided advantages in diagnosing placenta accreta in women who had posterior placental location [16]. We found that MRI was selected as a significant finding in predicting placenta accreta in pregnant women with placenta previa by univariate analyses in the prospective study (OR, 24.6; 95% CI, 4.7–129.2; p < 0.01) [9].

However, other investigators claimed that MRI was more expensive and invasive examination than US; therefore, US should be the diagnostic modality of first choice for placenta accreta, and MRI was not always necessary [17]. Dynamic contrast-enhanced MRI with gadolinium (Gd) is not recommended at any time during pregnancy, because the use of Gd increases the risk of a broad set of rheumatological, inflammatory, or infiltrative skin conditions and of stillbirth or neonatal death [18].

#### **2.3. Diagnostic scoring systems**

Diagnostic scoring systems may be more useful than a single US finding for predicting placenta accreta in women with a history of previous CS, placenta previa, or low-lying placenta [19–21]. These scoring systems include several US findings suggestive of placenta accreta, the presence of placenta previa, and the number of prior CS. Optimal cut-off values of these scores determined in the retrospective or prospective studies yielded 72.0–94.2% sensitivity, 52.5–85.0% specificity, 63.4–70.0% PPV, and 86.0–100% NPV for the prediction of placenta accreta [19–21].

We devised a novel scoring system for predicting placenta accreta in women with placenta previa, and in a prospective cohort study evaluated the diagnostic efficacy of this scoring system named the placenta previa with adherent placenta (PPAP) score [11]. The PPAP score is composed of two categories: (1) past history of CS, surgical abortion, and/or uterine surgery and (2) US and MRI findings. Each category is graded as 0, 1, 2, or 4 points, yielding a total score between 0 and 24 (**Table 1**).

PPAP scoring failed to predict two women with placenta accreta. One woman had a history of myomectomy and PPAP score of 6 and another had a past history of myometrium resection for adenomyosis and PPAP score of 4. The presence of a history of myomectomy and myometrium resection for adenomyosis seems to increase the risk for placenta accreta in women who had PPAP score < 8. Special attention should be paid to the risk of placenta accreta regardless

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All pregnant women with placenta previa suspected to have placenta accreta should be managed at specialized tertiary centers [22]. Their deliveries should be performed by an experienced medical team consisted of obstetric surgeons, urologists, general surgeons, and gynecologic oncologists [23]. Planned cesarean hysterectomy decreases the morbidity and mortality rates in women complicated by placenta accreta [3]. The timing of delivery in such women must be individualized; however, a recent study suggested that delivery at 34 weeks of gestation (GW) in stable women with placenta accreta optimized the outcomes of both mothers and neonates [24]. The anesthesiologists should assess which anesthetic techniques are used before delivery. Both general and regional anesthetic techniques are available, and the decision of which type of technique to be used should be made on an individual basis [23]. Preoperative cystoscopy with placement of ureteral stents may help prevent accidental urinary tract injury. In addi-

**3. The management of placenta accreta in women with placenta** 

tion, sufficient amount of blood products should be available in the operating room.

method is often used to avoid the placenta and allow delivery of the infant.

when women are willing to accept the risks involved in this approach.

by suitable approaches in each medical institution.

Planned preterm cesarean hysterectomy with the placenta left in situ is generally recommended for women with suspicion of placenta accreta, because forced removal of the placenta causes massive hemorrhage. Midline vertical incision may be considered because it provides sufficient exposure if hysterectomy is needed. CS using transverse uterine fundal incision

Hysterectomy is performed in the usual fashion. In some cases with anterior placenta accreta, especially in cases with placenta percreta, partial resection of the bladder wall is necessary. On the other hand, if the women have a strong desire for future fertility, conservative approach, i.e. leaving the placenta in situ, may be considered. However, a review, which summarized the conservative management of 60 women with placenta accreta, showed that infection occurred in 11 of the 60 women (18%), bleeding in 21 (35%), and disseminated intravascular coagulation in 4 (7%) [25]. Therefore, this conservative approach should be considered only

There has been lack of sufficient evidence for beneficial effects of prophylactic catheter placement for balloon occlusion or artery embolization [26–28] as well as treatment with methotrexate [29–31] . Therefore, a firm recommendation on the use of these procedures cannot be made [23, 31]. It is difficult to establish evidence-based management strategies for placenta accreta in pregnancy with placenta previa. Therefore, clinicians should manage these women

of US or MRI findings.

**previa**

Women with placenta previa who had PPAP score ≥ 8 were considered to be at a high risk for placenta accreta. The PPAP score yielded 91.3% sensitivity, 98.0% specificity, 87.5% PPV, and 98.7% NPV for predicting placenta accreta in women with placenta previa [11]. However, the


PPAP, placenta previa with adherent placenta; CS, cesarean section; USG, ultrasonography; and MRI, magnetic resonance imaging.

**Table 1.** The variables and scores in the PPAP scoring system.

PPAP scoring failed to predict two women with placenta accreta. One woman had a history of myomectomy and PPAP score of 6 and another had a past history of myometrium resection for adenomyosis and PPAP score of 4. The presence of a history of myomectomy and myometrium resection for adenomyosis seems to increase the risk for placenta accreta in women who had PPAP score < 8. Special attention should be paid to the risk of placenta accreta regardless of US or MRI findings.
