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 conclusions. The results suggest that there are relatively consistent patterns in the sensitivity to painful stimulation. These patterns are similar across stimulus modality with the exception of electrical stimulation. The magnitude of the effect was approximately 0.40 across all stimulation. For pressure stimulation, cold pressor pain, thermal heat stimulation, and ischemic muscle pain, a clear pattern emerges with the follicular phase demonstrating higher thresholds than later phases. When the effect size was pooled across studies (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 similar for tolerance measures. Electrical stimulation was different than the other stimulus modalities, showing the highest thresholds for the luteal phase. When the effect size was pooled across studies for electrical stimulation, effect sizes were small to moderate (menstrual (d(thr) = -0.37), follicular d(thr) = -0.30) periovulatory d(thr) = -0.61), and premenstrual d(thr) = 0.35) phases. This paper raises several important questions, which are yet to be answered. How much and in what way does this menstrual cycle effect bias studies of female subjects participating in clinical trials? Furthermore, how should studies of clinical pain samples control for menstrual related differences in pain ratings and do they exist in clinical pain syndromes? What this paper does suggest is that the menstrual cycle effect on human pain perception is too large to ignore.