The cardinal symptom of perimenopause is menstrual irregularity — cycles that become shorter, longer, heavier, lighter, or simply unpredictable after years of relative regularity. This irregularity reflects declining ovarian reserve and increasingly erratic estrogen fluctuation. Hot flashes and night sweats — vasomotor symptoms — are present in 75–80% of women during the menopausal transition and can begin years before periods stop. They are caused by narrowing of the thermoregulatory neutral zone in the hypothalamus due to declining estrogen.
Beyond the classic symptoms, perimenopause drives a constellation of changes that are frequently unrecognized as hormonal: sleep disruption (often driven by night sweats but also by direct estrogen effects on sleep architecture), mood changes including increased anxiety and irritability, brain fog and memory difficulties, joint pain, vaginal dryness and genitourinary symptoms (GSM — genitourinary syndrome of menopause), and changes in libido. These symptoms are real, physiologically driven, and treatable.
The diagnosis of perimenopause is clinical — based on age, menstrual pattern, and symptom constellation. FSH and estradiol levels are highly variable during perimenopause and are not reliable diagnostic tools except at the extremes. AMH (anti-Müllerian hormone) provides a better estimate of ovarian reserve. Thyroid function, anemia, and mood disorders must be excluded as contributing factors — they are common in this age group and amplify perimenopausal symptoms.
Hormone therapy (HT) — specifically, low-dose estrogen with progesterone (for women with a uterus) — is the most effective treatment for vasomotor symptoms and has broader benefits for bone density, cardiovascular risk (when started early), genitourinary symptoms, and sleep. The historical overcorrection following the 2002 WHI study resulted in massive underuse of HT in appropriate candidates. Current evidence, including the Menopause Society (formerly NAMS) guidelines, supports individualized HT in healthy women under 60 and within 10 years of menopause onset.