Assessment of the 2D : 4D Digit Ratio in Women With Fibromyalgia: Traces of Prenatal Hormonal Exposure

OBJECTIVES: Fibromyalgia is a chronic pain syndrome predominantly affecting women, characterized by widespread pain, fatigue, sleep disturbances, and cognitive impairment, yet lacks objective diagnostic biomarkers. The 2D:4D digit ratio is considered an indirect marker of prenatal sex hormone exposure, with lower values reflecting greater fetal androgen influence. This study aimed to evaluate the 2D:4D digit ratio in women with fibromyalgia and assess its potential as a noninvasive biomarker. METHODS: Fifty-seven female fibromyalgia patients (2016 ACR criteria) and 32 age-matched healthy female controls were enrolled. Index and ring finger lengths were measured bilaterally using digital calipers, and group comparisons were performed with Welch's t-test and Mann-Whitney U test. RESULTS: Mean age was comparable between groups (p = 0.685). Both the right 2D:4D ratio (0.991 ± 0.031 vs. 1.022 ± 0.016; p < 0.001; Cohen's d = -1.18) and the left 2D:4D ratio (0.999 [IQR 0.975-1.023] vs. 1.021 [IQR 1.013-1.034]; p < 0.001; Cohen's d = -0.98) were significantly lower in patients. CONCLUSION: Women with fibromyalgia exhibit significantly lower 2D:4D digit ratios in both hands compared to healthy controls, with the right hand demonstrating greater discriminative power. These findings suggest an association between digit ratios and fibromyalgia, pointing to potential observational links with prenatal hormonal proxy markers that warrant further mechanistic investigation. The right-hand 2D:4D ratio is simple, painless, and inexpensive to measure, and might therefore be worth exploring as a potential supportive parameter in future research. Larger multicenter studies are warranted to validate these findings across different populations.