Table 1.

Evidence salient to the hypothesis that endometriosis involves relative extremes of phenotypes that show evidence of sex differences in humans, due to genetic and environmental effects during development

Trait	Female–male sex difference, or variation among females	Pattern in endometriosis or its symptoms	References
Anogenital distance	Shorter in females than in males	Shorter in women with endometriosis compared to control women	[40, 41]
2D4D digit ratio	Longer in females than in males	Longer in women with heavy menstrual bleeding and dysmenorrhea (menstrual pain during periods caused by contractions)	[46]
Waist-to-hip ratio	Lower in women than in men	Lower in women with endometriosis than in control women	[47]
Inflammation levels	Higher in women than in men, during reproductive period of female life history	Higher in women with endometriosis compared to control women and men	[21, 48]
Pain (chronic)	Higher sensitivity in women than in men, and lower β-endorphin levels in women	Higher sensitivity to pain, and lower β-endorphin levels, in women with endometriosis compared to controls	See text for details
Serum testosterone	Lower in women than men	Lower in women with endometriosis than in controls	[49]
Serum oxytocin	Higher in women than in men	Higher in women with endometriosis than in control women	[50, 51]
Timing of menarche and menopause	Varies among females	Earlier menarche and menopause in women with endometriosis	[52, 53]
Length of menstrual cycle	Varies among females	Shorter menstrual cycle length in women with endometriosis	[54]
Dysmenorrhea	Varies among females	Higher levels in women with endometriosis	[55]
Bleeding during menstruation	Varies among females	Higher levels in women with endometriosis	[55]