Measurement of Obstetric Conjugate Diameter by Transabdominal Ultrasonograghy During Pregnancy and Comparison of Its Size with the Type of Delivery

Introduction: Normal morphological features of the maternal pelvis are an important prerequisite for vaginal delivery. Clinical evaluation and radiopelvimetry are the accepted methods for the evaluation of the maternal pelvis.But while the clinical method is associated with a subjective error, radiopelvimetry is cumbersome and associated with radiation hazard to the fetus, the ultrasonic measurement of obstetric conjugate is stated to be simple, cost effective,and clinically useful in women with suspected inlet obstruction. This study aimed at evaluating the relationship of ultrasonic measurement of the obstetric conjugate with the type of delivery. "nMaterials and Methods: In a diagnostic value study, 200 primigravidae with a cephalic presentation referred to 2 ultrasonography centers were recruited during a 14-months period. The obstetric conjugate diameter was measured twice by the means of transabdominal gray-scale ultrasonography at weeks 25-30 and 30-35 of pregnancy and the mean was employed as the main reading. The optimal cut-off point for predicting vaginal or cesarean delivery was calculated by the ROC curve. "nResults: Two hundred pregnant women with the mean age of 24.12± 4.94 (15-40) years were enrolled. Finally, the cesarean section (CS) was indicated in 65 (32.5%) patients. There was no significant difference between the first and the second measurements (p=0.065).According to the ROC curve analysis ,the optimal cut-off point for the obstetric conjugate diameter was > 119.75mm in prediction of vaginal delivery with a sensitivity and specificity of 80% and 78.5%, respectively."nConclusion: According to this study the ultrasonic measurement of obstetric conjugate is an accurate method which almost remains constant during the end of pregnancy; it's easy to be measured and might be confidentially employed for predicting the CS. Almost 80% of women with a reading of > 120mm could be expected to end up with the vaginal delivery. Below 100mm C/S is inevitably expected.