Lesbian and bisexual women may have different levels of sex hormones compared to heterosexual women. We systematically reviewed comparative studies measuring any sex hormones. A protocol was prospectively registered (PROSPERO-CRD42017072436) and searches conducted in six databases. Any relevant empirical studies published within the last 50 years reporting any circulating sex hormones in sexual minority women compared to heterosexual women were included, with no language or setting restrictions. Inclusions, data extraction, and quality assessment were conducted in duplicate. Random-effects meta-analyses of hormone levels, using standardized-mean-differences (SMD) were conducted where five or more studies reported results. From 1236 citations, 24 full papers were examined and 14 studies of mixed designs included, 12 in women without known ovarian problems. Hormones were measured in plasma (n = 9), saliva (n = 4), and urine (n = 2) and included androstenedione, luteinizing hormone, estradiol, pregnanediol, progesterone, testosterone, and several other hormones. Most studies were small, biased, and had considerable heterogeneity. Few found statistically significant differences between groups. All-sample meta-analysis showed increased testosterone in sexual minority women compared to heterosexual women (n = 9; SMD = 0.90; 95% Confidence interval (CI) 0.22, 1.57, I2 = 84%). This was the only difference found. We conclude that the small amount of heterogeneous research, from 50 years to date, suggests little discernable difference in sex hormone levels between lesbian, bisexual, and heterosexual women excepting possibly higher testosterone. A large-scale primary study would be required before placing any certainty in the findings or their implications.
Keywords: Bisexual women; Lesbian; Meta-analysis; Sex hormones; Sexual orientation.