A Systematic Review of Labor Pain Used as an Outcome Criterion in Clinical Research

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Research on labor pain currently uses standard scores such as numerical scales as clinical outcomes, but no clear guidelines for such an assessment have appeared since a review published in 1998. We aimed to describe and estimate the quality of the methods used to assess and analyze such outcomes in a systematic review of 215 comparative studies published since then in 27 influential journals.


In addition to a complete description, we created for each study a composite “analysis quality score” (AQS) on the basis of the methods of both measurement of pain/analgesia, and statistical analysis. AQS was tested against various factors, including a “design quality score” (DQS), created to estimate methodological quality (regardless of the analysis of pain intensity).


Both the AQS and its “measurement” component increased with the year of publication, as well as the DQS. The impact factor correlated only with the statistical component of the AQS, and with the DQS. However, the mean AQS and DQS were, respectively, at 43% and 75% of their maximal possible value, and these 2 scores were not correlated. The intensity of labor pain (or pain relief) was the primary outcome in 19% of the studies. Although most of the studies actually used numerical scales, the methods of analysis were heterogeneous. When a cutoff point was determined to define analgesia, this was most often 30% of the maximal value.


This review points out the need for a better standardization of the methods in this field of research.

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