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[Comparison of perineal sonography and abdominal ultrasound examination in placenta praevia]
This study describes a comparison between two different ultrasound methods used to localize a low-lying placenta or a placenta previa. The methods implemented were the abdominal ultrasound and the so-called "perineal scan", an ultrasound examination of the female urogenital tract, which is performed by using the perineum as an acoustic window. Between 1985 and 1988, 84 patients, suspected of having a low-lying placenta, were examined by perineal scanning. In all these cases it was possible to compare the results with those of abdominal ultrasound examinations documented in the patient's records. The "perineal scan"-examinations were performed "blind", i.e., without knowledge of the results of prior abdominal ultrasound. Abdominal sonography was performed by a different examiner using the full-bladder-technique. Perineal scanning was done a short time after voiding. The results showed considerable and significant (p less than 0.001) discrepancies between the two methods; perineal scanning more often demonstrated higher grade diagnoses (27 patients, 32%) than vice versa (9 patients, 11%). These differences may be at least partially explained by the influence of bladder distension. Probably a full bladder produces false negative results more often than previously suspected. An analysis of pregnancy outcome yielded positive predictive values of 78% (abdominal ultrasound) and 86% (perineal scanning). Perineal scanning therefore seems to provide an uncomplicated and reliable means to verify an abdominal placenta localisation.
This study describes a comparison between two different ultrasound methods used to localize a low-lying placenta or a placenta previa. The methods implemented were the abdominal ultrasound and the so-called "perineal scan", an ultrasound examination of the female urogenital tract, which is performed by using the perineum as an acoustic window. Between 1985 and 1988, 84 patients, suspected of having a low-lying placenta, were examined by perineal scanning. In all these cases it was possible to compare the results with those of abdominal ultrasound examinations documented in the patient's records. The "perineal scan"-examinations were performed "blind", i.e., without knowledge of the results of prior abdominal ultrasound. Abdominal sonography was performed by a different examiner using the full-bladder-technique. Perineal scanning was done a short time after voiding. The results showed considerable and significant (p less than 0.001) discrepancies between the two methods; perineal scanning more often demonstrated higher grade diagnoses (27 patients, 32%) than vice versa (9 patients, 11%). These differences may be at least partially explained by the influence of bladder distension. Probably a full bladder produces false negative results more often than previously suspected. An analysis of pregnancy outcome yielded positive predictive values of 78% (abdominal ultrasound) and 86% (perineal scanning). Perineal scanning therefore seems to provide an uncomplicated and reliable means to verify an abdominal placenta localisation.