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
Condition: Placenta Accreta Spectrum
MeSH terms: Placenta Accreta; Placenta Previa
Study type: Observational

Summary: 
      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.
    

Detailed description: 
      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.
    

Intervention name(s): Ultrasound measurment of placental thickness
Intervention type(s): Diagnostic Test
Intervention description(s): The maximum placental thickness in the lower uterine segment will obtained using trans-abdominal ultrasound scan. For the image to be deemed suitable, a midline sagittal section of the lower uterine segment (with the implanted placenta) and the cervical canal, with the intervening urinary bladder will be required (Bhide et al., 2019). The measurement will be performed by a researcher who will be blinded to the final diagnosis.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Pregnant women with placenta Previa attending outpatient obstetric clinic at Ain Shams
        University Maternity Hospital
      
Biospecimen description: 
      Cases with morbidly adherent placenta who will undergo cesarean hysterectomy will have thier
      uteri sent for histopathologic examination