When your periods are irregular

The menstrual cycle is counted from the first day of bleeding to the first day of the next period. It is therefore compared by the number of days, rather than by the calendar date. You can note when bleeding starts, how long it lasts and whether you bleed between periods.

A one-off change is different from a clear pattern of changes over several months. Hormonal contraception can also change or stop bleeding without this meaning that illness has interrupted your natural menstrual cycle. Mention which method you use when asking for advice.

The hormonal system takes time to settle into a more stable pattern after the first period. Cycles can therefore be irregular during adolescence.

Illness, physical and emotional demands, insufficient energy intake and changes in exercise or body weight can affect the hormones that regulate the menstrual cycle. Pregnancy is a possible explanation if sperm may have entered the vagina. Some people need assessment for hormonal conditions or other causes.

Describe what has changed rather than trying to diagnose yourself. If your periods stop, the doctor may ask about food, activity, stress, medication and other symptoms. The conversation should focus on your health and the support you need.

If you have had sex that could result in pregnancy, pregnancy should always be considered as one possible explanation for a missed period.

Talk with a school nurse or doctor if your period is absent for a prolonged time, the pattern changes substantially or you have other symptoms that concern you.