Abnormal hypervascularity in placenta accreta spectrum disorders: when to expect severe blood loss during surgical delivery

BACKGROUND: One of the principal indications of placenta accreta is pathological vascular remodeling in the region of the placental site. This phenomenon, which may result from various mechanisms, can give rise to significant blood loss in women undergoing cesarean section [2].

AIM: The study aims to evaluate the correlation between different types of abnormal hypervascularization observed on pelvic magnetic resonance imaging in pregnant women with placenta accreta and blood loss during surgical delivery by cesarean section.

MATERIALS AND METHODS: A total of 224 patients in the second and third trimesters of pregnancy with placenta previa and placenta accreta were examined. This was confirmed by ultrasound and magnetic resonance imaging, and subsequently by histopathologic examination. The mean age of the patients was 34.8±0.41 years (M±SE, p >0.05). Magnetic resonance imaging was conducted in accordance with a three-stage protocol on tomographs with magnetic field strengths of 1.5 and 3 Tesla. The diagnosis of placenta accreta was based on 11 signs, as outlined in the joint consensus statement of the Society of Abdominal Radiology and the European Society of Urogenital Radiology [1]. In addition, signs of hypervascularization were evaluated, including intrauterine (retroplacental, intramural, and subserosal) and extrauterine (parametrial, paracervical, and uterine-ovarian anastomosis zone) regions. The diagnostic criteria for hypervascularization were defined as an increase in the diameter of vessels, as indicated by areas of magnetic resonance signal dropout, their pronounced tortuosity, and their location in the corresponding anatomical regions relative to the uterus. Blood loss during labor was assessed in five categories: 1000 mL, 1000–1500 mL, 1500–2000 mL, 2000–3000 mL, and >3000 mL [3]. The correlation between variables was assessed using linear regression and Pearson’s correlation coefficient (r) and one-way analysis of variance. Differences were considered statistically significant at p <0.05.

RESULTS: According to the data of correlation analysis, the formation of anterior (r=0.3591, p <0.0001) and lateral (r=0.2799, p <0.0001) parametrial vascular collateralization, as well as utero-ovarian anastomosis (r=0.1369, p=0.0407) had the most significant effect on the severity of postpartum hemorrhage. There was no statistically significant effect of retroplacental hypervascularization on the increase in blood loss volume (r=–0.01611, p=0.6051).

CONCLUSIONS: The study demonstrated that patterns of abnormal vascular remodeling in the placental site can be clearly identified by magnetic resonance imaging and used as a predictor of severe hemorrhage. Pregnant women with such MRI findings should be referred to a level 3 perinatal center to ensure adequate control of increased risks of obstetric hemorrhage during operative delivery.