Background: Detection of women at risk for dystocia will allow physicians to make preparations and treatment decisions that can minimize maternal and neonatal morbidity. We aimed to determine the risk factors for dystocia in nulliparous women. Methods: This case series enrolled 447 nulliparous women who presented with a single pregnancy in the vertex presentation and gestational age of 38-42 weeks. Maternal anthropometric measurements were obtained upon admission. We defined dystocia as a cesarean section or vacuum delivery for abnormal progression of labor as evidenced by the presence of effective uterine contractions, cervical dilation of less than 1 cm/h in the active phase for 2 h, duration of the second stage beyond 2 h, or fetal head descent less than 1 cm/h. Data were analyzed by SPSS software version 11.5. Kruskal-Wallis, logistic regression, chi-square, Student’s t test and the Mann-Whitney tests were used as appropriated.Results: The state anxiety score (OR=10.58, CI: 1.97-56.0), posterior head position (OR=9.53, CI: 4.68-19.36), fetal head swelling in the second stage of labor (OR=6.85, CI: 2.60-18.01), transverse diagonal of Michaelis sacral ≤9.6 cm (OR=6.19, CI: 2.49-15.40), and height to fundal ratio <4.7 (OR=2.68, CI: 1.09-10.60) were significant risk factors for dystocia.Conclusion: Critical care during labor and delivery in women who have a height to fundal height ratio of <4.7 or transverse diagonal of Michaelis sacral ≤9.6 cm, an anxiety score greater than moderate, and posterior head position or fetal head swelling during the second phase could play an effective and important role in preventing dystocia.