Correlation between subjective labour pain and uterine contractions: a clinical study

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Abstract
Fifteen primiparous women underwent tocography during the second phase of the first stage of labor in order to evaluate the main characteristics of their uterine contractions (intensity, duration and pattern). At th end of each contraction, for a total of about 8 contractions per woman and an overall total of 125 tocographic curves, each women was asked to make a subjective evaluation of the pain felt during that contraction using a 10 cm visual analogue scale (VAS). All the tocographic curves corresponding to the contractions studied were elaborated mathematically to determine the peak (intensity), base (duration) and area under the curve (AUC). Lastly, correlations between the mathematical parameters of the curves and corresponding VAS scores were sought. In the population a general positive correlation between the 3 main parameters of tocographic curves and the VAS scores was demonstrated; the AUC and the peak tended to be better correlated with VAS than duration. Within-subject comparison showed the existence of a significant correlation with VAS score in 12/15 women as far as peaks are concerned, in 10/15 as far as AUC is concerned and in 0/15 women as regards duration. The findings support the concept that perceived labor pain depends in most of the women on the intensity and pattern of the uterine contractions. The possible clinical and experimental applications of this finding are discussed.