A meta-analytic review of pain perception across the menstrual cycle

The purpose of this article is to review the sixteen published studies that examine associations between the perception of experimentally induced pain across menstrual cycle phases of healthy females. We also performed a meta -analysis to quantitatively analyze the data and attempt to draw conclusion s. The results suggest that there are relatively consistent patterns in the sensitivity to painful stimulation. These patterns are similar across stim ulus modality with the exception of electrical stimulation. The magnitude o f the effect was approximately 0.40 across all stimulation. For pressure st imulation, cold presser pain, thermal heat stimulation, and ischemic muscle pain, a clear pattern emerges with the follicular phase demonstrating high er thresholds than later phases. When the effect size was pooled across stu dies (excluding electrical) comparisons involving the follicular phase were small to moderate (periovulatory phase, d(thr) = 0.34; luteal phase, d(thr ) = 0.37; premenstrual phase, d(thr) = 0.48). The pattern of effects was si milar for tolerance measures. Electrical stimulation was different than the other stimulus modalities, showing the highest thresholds for the luteal p hase. When the effect size was pooled across studies for electrical stimula tion, effect sizes were small to moderate (menstrual (d(thr) = -0.37), foll icular d(thr) = -0.30) periovulatory d(thr) = -0.61), and premenstrual d(th r) = 0.35) phases. This paper raises several important questions, which are yet to be answered. How much and in wha way does this menstrual cycle effe ct bias studies of female subjects participating in clinical trials? Furthe rmore, how should studies of clinical pain samples control for menstrual re lated differences in pain ratings and do they exist in clinical pain syndro mes? What this paper does suggest is that the menstrual cycle effect on hum an pain perception is too large to ignore. (C) 1999 international Associati on for the Study of Pain. Published by Elsevier Science B.V.