Perimenopause vs PCOS: How to Tell the Difference
Irregular periods, weight gain, and mood changes appear in both perimenopause and PCOS. Learn how these two conditions differ and why correct diagnosis matters.
Two Conditions That Are Easily Confused
Polycystic ovary syndrome (PCOS) and perimenopause share several prominent symptoms, including irregular or absent periods, weight changes, mood disruption, and fatigue. For women who were diagnosed with PCOS in their 20s or 30s and are now entering their 40s, the question of whether new or worsening symptoms reflect their existing condition or the onset of perimenopause is genuinely complex. For women who have never been diagnosed with either, irregular periods and associated symptoms during the mid-40s can look like either condition on the surface. Getting the correct picture matters because the management approach for each is quite different.
What PCOS Involves
PCOS is a hormonal and metabolic condition that affects roughly one in ten women of reproductive age. It is characterised by irregular or infrequent ovulation, elevated androgens (male hormones such as testosterone), and polycystic-appearing ovaries on ultrasound. A diagnosis of PCOS requires at least two of these three features under current Rotterdam criteria. PCOS is associated with insulin resistance in many cases, and with increased risk of type 2 diabetes, cardiovascular disease, and metabolic syndrome over time. Symptoms of PCOS include irregular periods, heavy or prolonged bleeding, difficulty conceiving, acne, excess facial or body hair (hirsutism), and scalp hair thinning.
What Perimenopause Involves
Perimenopause is the natural transition toward the end of the reproductive lifespan, typically beginning in the mid-to-late 40s, during which ovarian hormone production becomes increasingly erratic and then declines. It is driven by a reduction in the quantity and quality of remaining egg follicles, which leads to rising FSH and falling estrogen and progesterone. Perimenopause is not a disorder. It is a normal biological transition. Key features include changes to menstrual cycle length, frequency, or flow, hot flashes, night sweats, sleep disruption, mood changes, brain fog, joint aches, and vaginal dryness. Symptoms can be mild and brief or severe and prolonged.
Overlapping Symptoms That Create Confusion
Irregular periods are the most obvious shared feature. Both PCOS and perimenopause cause cycles that are unpredictable, too frequent, too infrequent, or that skip months entirely. Weight gain, particularly around the abdomen, occurs in both, though driven by different mechanisms: insulin resistance and androgen excess in PCOS, and declining estrogen with associated metabolic changes in perimenopause. Mood changes including anxiety, low mood, and irritability appear in both conditions. Hair thinning occurs in perimenopause as estrogen declines, and in PCOS as a result of androgen-related effects on hair follicles. Fatigue and difficulty sleeping are also common to each.
Symptoms That Point More Toward PCOS
Hirsutism, meaning unwanted hair growth on the face, chin, chest, or abdomen, is a characteristic PCOS feature driven by elevated androgens. This does not typically arise from perimenopause alone, though the relative increase in androgen effects as estrogen falls can sometimes give the impression of increased facial hair. Acne in adult women, particularly cystic acne along the jawline, is more characteristic of androgen excess than of estrogen decline. A polycystic-appearing ovary on ultrasound, combined with irregular periods and elevated androgens on a blood test, meets the criteria for PCOS regardless of age. Infertility due to infrequent ovulation in a woman of reproductive age is another PCOS indicator.
Symptoms That Point More Toward Perimenopause
Hot flashes and night sweats are the most specific perimenopause indicators and do not arise from PCOS. A clear age context matters: a 48-year-old woman with recently irregular periods and new hot flashes has a much higher prior probability of perimenopause than PCOS. Vaginal dryness and discomfort during sex reflect estrogen-related tissue thinning and are features of perimenopause rather than PCOS. A rising FSH on blood testing, particularly two or more elevated FSH results taken at least four weeks apart, points strongly toward perimenopause. Estradiol levels that are low or erratically low are another indicator of the perimenopausal transition.
When PCOS and Perimenopause Both Apply
Women with PCOS do go through perimenopause, and some evidence suggests they may experience a slightly later onset of menopause than women without PCOS, possibly because the larger follicle reserve characteristic of polycystic ovaries takes longer to deplete. However, this is not universal and should not be assumed. A woman in her late 40s with a long-standing PCOS diagnosis who develops new hot flashes and sleep disruption deserves investigation for perimenopause in addition to ongoing PCOS management. Blood testing for FSH, estradiol, LH, testosterone, and SHBG can help disentangle the two. Tracking symptoms and cycle changes over several months in a consistent log, such as PeriPlan, gives both you and your clinician the clearest possible picture of what is happening and when.
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