INTRODUCTION
Placenta previa often occurs in pregnant women who have had increased age, multiple gestations, high parity, and smoke or use illegal drugs (1). Cesarean delivery induced scar formation in uterine and endometrial injuries also facilitates the development of placenta previa in the subsequent pregnancies of women (2,3). It is estimated that placenta previa occurs in 0.28-0.55% of pregnant women in the USA (4). The overall incidence of placenta previa in China has recently been reported to represent 1.24% of deliveries (5). Placenta previa can cause severe maternal and neonatal complications including the limitation of fetal growth, preterm birth, hemorrhage whatever the degree of overlying placenta and gestation stage, hysterectomy and even the mortality of the fetus and mother (6,7).
To avoid these consequences, cesarean section has been widely applied in pregnancies with placenta previa. However, despite its important role in managing dystocia, pregnancy complications, and reducing maternal and child mortality and morbidity, cesarean delivery rates have increased around the world (8,9). For example, in China, it increased from about 5% in the 1960s to 20% in the late 1980s and early 1990s (10). In particular, cesarean sections made of 40-60% of deliveries in most hospitals in China during the last 20 years (11,12). On the other hand, cesarean history increases the risk of placenta previa by 60% in the subsequent pregnancy of women (13). A pregnant woman who has both a complete placenta previa and cesarean history is more likely to have high risk of placenta implantation, severe bleeding during gestation and delivery, and massive postpartum hemorrhage (14,15). More seriously, in the case where the placenta grows on the scar of a previous cesarean section, referred to as pernicious placenta previa, increases the risk of placenta implantation by up to 50% (16). Both pernicious placenta previa and placenta implantation are very critical and urgent situations in obstetrics, in which fatal bleeding occurs very often during delivery, and the maternal mortality rate is as high as 7% (17). However, no collective data have been reported up to now to demonstrate the severe outcomes and associated risk factors in patients with pernicious placenta previa. To prevent severe bleeding during delivery and severe postpartum hemorrhage in these patients, vascular occlusion has been widely used in clinical practice, with methods such as bilateral uterine artery embolization (UAE), internal iliac artery embolization (IIAE) and intra-aortic balloon occlusion (18,19), although their anti-bleeding effect and influence on the prognosis of pregnancies remain unclear.
We performed a retrospective study in which data on 747 patients who had pernicious placenta previa in their pregnancy following their first cesarean delivery, were collected from 13 first-class hospitals located in different regions of China. The severe consequences and associated risk factors of these patients were analyzed. In particular, we evaluated the approaches taken to predict severe outcomes and the influence of vascular occlusion in preventing severe postpartum hemorrhage and hysterectomy.