the shape of uterine contractions and labor progress in the spontaneous active labor

background: dystocia is the most common indication of primary cesarean section. the most common cause of dystocia is uterine dysfunction. in prolonged labor, more attention is usually paid to the fetus and pelvis rather than to the role of uterine contractions in a delivery. therefore, we decided to determine the relationship between the labor progress and uterine contractions shapes . methods: in this cross-sectional study, 200 primiparous women participated having a single pregnancy and cephalic presentation. uterus contractions were recorded using electronic fetal monitoring at the beginning of the active phase of labor (dilatation 3-5 cm) for 30 min. fall to rise (f:r) ratio was calculated by determining the duration of returning from a contraction peak to its baseline (fall) and the duration of the rise time from baseline to peak (rise) in two groups. the data were analyzed using t-test and chi-square test. results: in this study, 162 women had a normal delivery and 38 women had a cesarean (cs) delivery due to the lack of labor progress. the average f:r ratio was 1.13±0.193 seconds in the vaginal delivery group and 1.64±0.301 seconds in the cs group. this difference was statistically significant (p<0.001). the frequency of contractions in the vaginal delivery group was more than the cs group (p=0.008). conclusion: our findings demonstrated that uterine contractions shapes change; and f:r ratio was higher in the group that lacked labor progress. therefore, contraction shapes can be used to predict the labor progress.