Comparison of the accuracy of trans-abdominal sonography (TAS) and transperineal sonography (TPS) in the diagnosis of Placenta Praevia

Abstract

Although the incidence of Placenta Praevia (PP) is low, its association with increased perinatal and maternal morbidity and mortality underscores the imperative of accurate pre-labour diagnosis. To compare through a prospective study, the accuracy, sensitivity and specificity of Trans-Abdominal Sonography (TAS) and Trans-Perineal Sonography (TPS) in the diagnosis of Placenta Praevia and to determine the causes, if any, of avoidable diagnostic errors. During the study period from 1999 to 2001, 133 patients were evaluated by TAS and TPS. The age ranged from 19-41 years while the gestational age ranged from 20-weeks to term. All had examination with 3.5 MHz mechanical sector real-time scanner (Siemens high-resolution Sonoline SL-1 ultrasound machine). The accuracy of TAS and TPS in diagnosing PP was then compared with surgical outcome in each patient. Out of the 133 patients diagnosed to have PP early on in pregnancy, 41 (30.8%) had persistent praevia till delivery, while in 92 (69.2%), the placenta converted to a normal location. The diagnosis at delivery confirmed the TPS diagnosis in 40 of 41 cases, while TAS diagnosis was confirmed in 39 of 41. TPS did not predict the delivery diagnosis in 1 patient where it ruled out a PP, TAS did not predict the delivery diagnosis in 2 patients who were believed not to have a clinically significant placenta praevia. In 1 patient TAS suggested PP but delivery diagnosis showed a normal placental implantation. The overall accuracy, specificity and sensitivity for TPS and TAS were 99.3%, 100%, 99.2% and 97.7%, 98.9%, and 95.1% respectively. TPS is a safe, accurate and rapid technique, which complement TAS for evaluation of patients with PP. In patients who decline this method however, graded bladder distension, Trendelenburg and traction scanning and determination of the absence of focal uterine contraction, which distorts the lower uterine segment, are techniques, which significantly improve the diagnosis of PP by TAS.