Perimenopause symptoms
Irregular periods
Menstrual cycle changes during perimenopause
Your periods have changed. Maybe they're coming earlier than they used to — one month 23 days, the next 30, the month after 19. Maybe they've become heavier, or lighter, or both at different times. Maybe you've skipped a month entirely and had a pregnancy test come back negative and been left without an explanation.
If you're in your 40s — or even your late 30s — and your periods have started doing things they didn't used to do, perimenopause may be the reason. For most women, a change in the menstrual cycle is the first sign that the hormonal transition toward menopause has begun.
Menstrual cycles are regulated by the interaction between the brain and the ovaries. During perimenopause, this system begins to fluctuate. The ovaries' supply of follicles diminishes, oestrogen levels become unpredictable, and ovulation becomes inconsistent. Some cycles are anovulatory — the body goes through the hormonal motions without actually releasing an egg. These changes produce the irregular, unpredictable periods that characterise perimenopause.
Begins when the cycle becomes persistently different — specifically, when cycle length varies by seven or more days from the usual pattern. This is the clinical marker established by the ReSTAGE Collaboration and adopted in the STRAW+10 consensus. In practice, this often means cycles becoming shorter and more variable.
Marked by a gap of 60 or more days without a period. This signals that ovulation has become rare and the hormonal environment is significantly altered. Women in late perimenopause may have a period after a 2–3 month absence, followed by another gap, before eventually reaching the final menstrual period.
Cycles may become shorter first and then longer. Periods may be lighter than usual at some stages and heavier at others. Spotting between periods can occur. Some women experience prolonged bleeding episodes.
Perimenopause begins earlier than many women expect. Research published in 2025 in npj Women's Health, analysing over 4,000 US women, found significant perimenopause-related symptom burden — including cycle changes — in women aged 30–45. For the majority of women, the transition begins in the mid-to-late 40s — but for some it starts in the early 40s, and in a small proportion before 40.
Irregular periods in perimenopause are common. But irregular periods are also a symptom of other conditions that require medical evaluation. Seek prompt medical assessment if:
- Bleeding is significantly heavier than usual — soaking through protection more quickly than normal, or passing large clots
- Bleeding lasts longer than seven to ten days
- Bleeding occurs after sex
- You have bleeding after a period of 12 months or more without one (postmenopausal bleeding always requires assessment)
- You have pelvic pain alongside irregular bleeding
Irregular cycles in perimenopause do not mean infertility. Ovulation does still occur — unpredictably — during the transition, and pregnancy remains possible throughout perimenopause until 12 months have passed since the final period. If you do not want to become pregnant, contraception should be discussed with your doctor regardless of how irregular your cycles have become.
A change in your menstrual cycle is a legitimate reason to see a doctor and to ask directly whether perimenopause might be relevant. It helps to be specific: when did you first notice the change? What has changed — timing, flow, duration, or all three? Have you noticed any other symptoms alongside it? Blood tests for FSH and oestradiol may be offered — but it is worth knowing these have significant limitations during perimenopause, as hormone levels fluctuate considerably and a single result can be misleading.
Irregular periods are the most visible sign that the menopausal transition has begun — but they rarely arrive alone. The Thea Klara survey covers all eight domains of perimenopause experience, so that your appointment summary reflects the full picture.
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Harlow SD, Paramsothy P. Menstruation and the Menopause Transition. Obstet Gynecol Clin North Am. 2011.
Harlow SD et al. The ReSTAGE Collaboration: defining optimal bleeding criteria. Fertil Steril. 2008.
Soules MR et al. STRAW+10: Addressing the Unfinished Agenda of Staging Reproductive Aging. Climacteric. 2012.
Santoro N et al. Helping midlife women predict the onset of the final menses: SWAN. Menopause. 2007.
Zhaunova L et al. Perimenopause symptoms, severity, and healthcare seeking. npj Women's Health. 2025.
Thea Klara provides self-advocacy tools, not medical advice. Postmenopausal bleeding and significantly abnormal uterine bleeding always require medical assessment.