Background and Aim: Detection of women at risk of dystocia could minimize the maternal and neonatal morbidity. The objective of our study was to determine The diagnostic accuracy of the combination of maternal height and transvers diagonal of Michaelis sacral rhomboid to predict dystocia in nulliparous women who referred to Ommolbanin Hospital of Mashade between December 2008 and June 2009. Materials and Methods: In this validity study of diagnostic methods we included 447 nulliparous women with a single pregnancy in vertex presentation and with gestational age of ≥ 38 weeks. The transvers diagonal of the Michaelis sacral rhomboid area and maternal height were assessed in cervical dilatation of ≤ 5 centimeters, then labor progress was monitored and dystocia was defined as caesarean section and vacuum or forceps delivery for abnormal progress of labor (at presence of effective uterine contractions, arrest of cervical dilatation or cervical dilatation less than 1 centimeter/hour in the active phase for 2 hours and duration of second stage more 2 hours or fetal head descend less than 1cm/h). Results: Maternal height ≤ 155 centimeters had a sensitivity of 50%, a specificity of 70/8% and an accuracy of 68/2%. The transverse diagonal of the Michaelis sacral rhomboid area ≤ 9/6 centimeter resulted in a sensitivity of 60/7%, a specificity of 84/1% and an accuracy of 81/2%. The highest sensitivity, specificity and accuracy were obtained from combination of maternal height tand transvers diagonal of Michaelis sacral and were respectively 89/4%, 90/7% and 86/2%. Conclusion: Transverse diagonal of the Michaelis sacral rhomboid area in comparison to maternal height was the better predictor of dystocia and its combination with maternal height results in a better indicator for prediction of dystocia. This method could predict 86/2% of cases of dystocia and normal vaginal delivery.

Keywords: Dystocia, prolonged labor, cephalopelvic disproportion, Transverse diagonal of the Michaelis sacral, maternal height.

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