RESUMEN
OBJECTIVE: To determine whether analysis of the frequency or regularity of uterine contractions can distinguish between women delivering vaginally and women requiring Cesarean section for dystocia. STUDY DESIGN: This was a case-control study. Cases meeting the following criteria were identified: nulliparous women in spontaneous labor, singleton pregnancy, cephalic presentation, 37 to 42 weeks' gestation, Cesarean section for dystocia, a minimum of three analyzable hours of electronically archived cardiotocograph (CTG) prior to onset of the second stage. Cases delivered by Cesarean section for dystocia were each matched with two controls delivering vaginally. The peak of each contraction was visually identified and electronically marked on each CTG trace. A moving average (MTIME) and standard deviation (SDTIME) of five interpeak times were calculated for successive 30-minute periods and plotted against cervical dilatation for each group. RESULTS: Overall, both MTIME and SDTIME fell as labor progressed, with these changes being more marked in the vaginal delivery group. In women requiring oxytocin, the rate of fall of MTIME and SDTIME was significantly greater following oxytocin in the group which subsequently delivered vaginally (slope of MTIME -2.71 pre-oxytocin and -28.95 post-oxytocin, p=0.0004; slope of SDTIME -0.44 and -6.44, p=0.0002). No such change was seen in the Cesarean section group. CONCLUSION: As normal labor progresses, there is a shortening of the intercontraction interval and an increase in contraction regularity. A successful response to oxytocin augmentation may be predicted by the change in contraction pattern following treatment.