Definition of pernicious placenta previa

The reason why placenta previa is dangerous is that it is very harmful to pregnant women, especially during delivery, it can easily cause dystocia and cause some unpredictable hazards. Therefore, if placenta previa occurs, a full diagnosis must be made before delivery to identify high-risk factors, such as imaging examinations, including ultrasound, etc.

Definition of pernicious placenta previa

In 1993, Chattopadhyay et al. prospectively analyzed the data of 41,206 deliveries and found that the incidence of placenta previa in patients with a history of cesarean section during subsequent pregnancy was higher than that in patients without a history of cesarean section (2.54% and 0.44%, respectively). Among patients with placenta previa with a history of cesarean section, the proportion of placenta accreta was also higher than that in those without a history of cesarean section (38.2% and 4.5%, respectively). Therefore, the concept of "catastrophe placenta previa" was recommended.

Prediction and diagnosis of pernicious placenta previa 1. Prenatal diagnosis: mainly based on high-risk factors, symptoms, signs and auxiliary examinations. Prepartum hemorrhage is more common in patients with pernicious placenta previa, but clinical symptoms and signs in patients with complete placenta accreta are less common before delivery. Therefore, pernicious placenta previa can be preliminarily diagnosed based on the presence of painless vaginal bleeding without obvious cause, high floating presenting part and abnormal fetal position in the second and third trimesters of pregnancy, and can be diagnosed in combination with imaging examinations. However, the prenatal diagnosis of patients with placenta accreta mainly relies on clinical high-risk factors combined with color Doppler ultrasound and/or MRI manifestations. Among them, the high-risk factors are mainly patients with a history of cesarean section but a history of intrauterine operation, such as myomectomy or curettage. When there is a high suspicion of placenta previa with placenta accreta and the diagnosis cannot be confirmed clinically, further relevant auxiliary examinations should be performed. 2. Imaging examination: mainly includes ultrasound examination and MRI. Ultrasound examination has the advantages of being non-invasive, low-cost, and able to be repeated, so it can be used as the preferred examination method for patients suspected of having invasive placenta previa. Ultrasound examination is of high diagnostic value for placenta previa. If ultrasound shows disordered normal uterine structure at the placental implantation site, diffuse or focal intracavitary blood flow in the placental parenchyma, thinning or disappearance of the normal hypoechoic area behind the placenta, and rich blood vessels at the uterine serosa-bladder junction, pernicious placenta previa with placenta accreta should be considered.