Endometriosis, polycystic ovary syndrome, and the thyroid: a review

Endometriosis and polycystic ovary syndrome (PCOS) are common gynecological disorders that constitute a significant burden of disease in women of fertile age. The disorders share a link to female reproduction and infertility; however, divergent effects on menstrual cycle, related hormones, and body composition have been proposed. Disorders of the thyroid gland including abnormal thyroid dysfunction (hyperthyroidism or hypothyroidism) and/or markers of thyroid autoimmunity similarly show a female predominance and onset in younger age groups. We reviewed the literature on the association between endometriosis, polycystic ovary syndrome (PCOS), and thyroid disease up until July 1, 2023, and identified eight original studies on endometriosis and thyroid disease, and 30 original studies on PCOS and thyroid disease. The studies were observational and heterogenous regarding the design, sample size, and definitions of exposure and outcome; however, a tendency was seen towards an association between hyperthyroidism and endometriosis. Especially an association between endometriosis and slightly elevated levels of thyroid stimulating hormone receptor antibodies has been found and corroborated in studies from different populations. On the other hand, the literature review turned a focus towards an association between hypothyroidism and PCOS, however, with uncertainties as to whether the association is caused by hypothyroidism per se and/or the thyroid autoantibodies (thyroid peroxidase and thyroglobulin antibodies). More evidence is needed to substantiate an association between endometriosis, PCOS, and thyroid disease, and to differentiate between the role of thyroid function and thyroid autoimmunity. Furthermore, studies are warranted to extend knowledge on the different disease characteristics and underlying mechanisms.