Fatigue, brain fog, weight gain, hair loss — classic perimenopause symptoms. Also textbook hypothyroidism. In midlife women, the overlap is so complete that one condition routinely masks the other, leaving thousands undiagnosed and untreated. Here's the science behind the perimenopause-thyroid connection, why a normal TSH result doesn't mean your thyroid is fine, and the six tests every perimenopausal woman should ask for — including the antibody tests that catch Hashimoto's