Diagnostic Accuracy of Placental Thickness in Lower Uterine Segment Measured By Ultrasound in Prediction of Placenta Accreta Spectrum in Patients With Placenta Previa. A Diagnostic Test Accuracy Study

Overview

Current prenatal diagnosis of placenta accrete spectrum disorders relies on subjective individual interpretations of visual sonographic findings on grayscale and color Doppler imaging. When blinded to clinical data, there is significant interobserver variability in the diagnosis of invasive placentation. This study will evaluate placental thickness among pregnant women with placenta previa and determine if increased placenta thickness correlates with the risk for placenta accreta spectrum (PAS) disorders.

Placenta accreta spectrum is one of the most dangerous conditions associated with pregnancy, because hemorrhage may result in multisystem organ failure, disseminated intravascular coagulation, need for admission to an intensive care unit, hysterectomy, and even death. The reported incidence of placenta accrete spectrum disorder has increased over time and is currently between 1 in 533 to 1 in 300 pregnancies. Prior cesarean delivery and especially multiple cesarean deliveries are major risk factors. The spectrum includes placenta accreta (attachment of the placenta to myometrium without intervening decidua), placenta increta (invasion of the trophoblast into the myometrium), and placenta percreta (invasion through the myometrium, serosa, and into surrounding structures). PAS is linked to placenta previa, and there is a lot of overlap in imaging findings between the two processes. PAS problems affect approximately 11% of people with placenta previa. Differentiating between placenta previa with and without PAS problems is crucial in clinical practice. A finding of placenta previa together with a history of cesarean delivery has long been an indication for counseling patients on their risk of PAS in a current pregnancy, as the risk for placenta accreta in the presence of placenta previa increases with each subsequent cesarean delivery. Aside from cesarean deliveries and placenta previa, other risk factors have been identified for PAS, including past uterine surgeries, in vitro fertilization (IVF), multiparity, maternal age, and even female sex of the infant. Prenatal diagnosis of AIP has been shown to reduce maternal morbidity associated with this condition, most likely due to the opportunity to plan management in advance. Ultrasound is the primary investigation for prenatal diagnosis of morbidly adherent placenta, and the diagnostic accuracy is good both in retrospective, as well as prospective case series. Placental localization with transabdominal sonography (TAS) has been a standard practice for a long time. Despite its availability and noninvasive nature, accuracy of TAS may be limited by many factors, such as the posterior implantation of placenta, being obscured by the fetal head, an under-filled or over-distended bladder, and presence of blood clots, fibroids, uterine contractions, and obesity. These limitations are overcome by transvaginal sonography (TVS), which provides a better resolution by using a higher frequency transducer, shorter distance from the transducer to the internal os, and is not affected by the over- or under-filling of the bladder. Although ultrasonography's sensitivity and specificity for detecting accreta have been reported to be excellent, ranging from 80 to 90%, there was considerable difference among "experts" in predicting whether PAS was present. With placental implantation into the cesarean section scar, the center of the placental disc would be in the vicinity of the lower uterine scar. If placental implantation was near the scar but not in it, only the thinner placental margin might encroach into the lower uterine segment. The investigators therefore hypothesized that the placenta is thicker with AIP in women with a low-lying placenta or placenta previa. So, the investigators hypothesize that placental thickness will be directly related to placental invasion in cases of placenta accrete spectrum.