Irregular cycles — what is variation, and what is a reason to talk

The textbook cycle lasts about 28 days, but few people have one "like clockwork". Cycle length differs between women and, in the same woman, from month to month — a degree of variation is ordinary and does not by itself mean illness.

There are times of life when irregularity is downright typical: the first years after the first period (cycles can take up to two years to settle), the time after childbirth and breastfeeding, and perimenopause — the years of change leading up to menopause. Rhythm is also shifted by stress, travel and illness — and, very often, by hormonal contraception: with some methods bleeding becomes irregular, light, or stops. If you use contraception or other medicines that affect the cycle, a change in bleeding is first of all a topic about the medicine — not a reason to stop it on your own.

When is an appointment worthwhile? A simple rule: when something has changed noticeably against your own usual pattern, or when the irregularity worries you or gets in the way of plans (for example, trying to conceive). You don't need to meet any threshold or "prove" anything — telling how it was and how it is now is enough. One piece of information helps at the appointment: the date of the first day of your last period; if you like, you can also note the dates of subsequent bleeds.

Regardless of everything else, report to a doctor: bleeding between periods, bleeding after sex, any bleeding after menopause — and if a period is missed and pregnancy is possible, take a pregnancy test first.

Urgent help: very heavy bleeding with weakness, dizziness or feeling generally unwell is a situation for urgent medical contact, not a routine appointment.

Sources: [1] NHS — Irregular periods; [2] NHS inform — Irregular periods.