Why your periods change first
Perimenopause is defined by shifting hormones, and your menstrual cycle is where that shift tends to show up before anything else. Early in the transition, the gap between periods often shifts by a week or more from one cycle to the next, and for many women it gets shorter at first, so periods come more often than they used to. Later, whole cycles get skipped and gaps of sixty days or more become common on the way to your final period (Journal of Clinical Endocrinology & Metabolism, 2021). In other words, your cycle stops behaving like a metronome and starts behaving more like weather, variable from month to month while still following a broad direction.
This is also why a single reading of anything, a hormone test on one day or one unusually early period, tells you very little. The signal is in the pattern over months, not in any one cycle, which is how perimenopause is actually recognised.
What counts as an ordinary change
Quite a wide range is normal, and it runs in both directions. Periods can arrive closer together, not only further apart, and coming more often is common early on, before the longer gaps set in. The flow can change a great deal too, and from one month to the next: some periods heavier than you are used to, others noticeably lighter, along with shorter or longer bleeds and the occasional missed month (Journal of Clinical Endocrinology & Metabolism, 2021).
Alongside the cycle changes, you might notice new symptoms turning up at the same time, broken sleep, hot flushes, mood changes, or aches, which is the body telling the same story from a different angle.
When to talk to a doctor
Some bleeding patterns deserve a proper look, not because they are usually serious, but because they have causes worth checking. See your doctor if your periods become very heavy, for example soaking through protection or passing large clots, if they come very close together, if you have bleeding between periods or after sex, or if you have any bleeding at all after twelve months without a period (NICE guideline NG23, 2024). None of these means something is wrong on its own, but each is a reason to be seen rather than to wait it out.
It is also worth remembering that a diagnosis is not the only reason to go. If your periods or symptoms are affecting daily life and you want to talk about options, that is reason enough. anna does not diagnose, and this article is not medical advice.