Why are my Periods Irregular?

Irregular periods are a form of abnormal uterine bleeding. A menstrual cycle is defined as the time from the start of one period to the start of the next. The average cycle is 28 days long; however, in reality this differs from woman to woman, and anything between 21 and 35 days is considered normal.

Irregular periods occur when one or more of the following is true:

  • The menstrual cycle is shorter than 21 days or longer than 35 days.
  • Bleeding lasts for 8 or more days.
  • The length of the menstrual cycle changes month by month and there is a difference of at least 20 days between the shortest cycle and the longest cycle.

If you suspect that your periods are irregular the first thing is to accurately calculate how long your cycle is and whether the time in days between each period is changing. Although some women will have cycles of exactly 28 days every month, it is not unusual for a cycle to differ by a few days each month. Your doctor will need to know the specifics of any irregularities. Count from the last day of your period to the first day of your next period for at least three months to see whether the value differs significantly between cycles.

As well as the inconvenience of not knowing exactly when you will start menstruating each month, irregular periods can make it difficult to get pregnant. In fact, as irregular periods make it hard to determine precisely when (and if) ovulation has occurred, women who experience them might also be at greater risk of falling pregnant unexpectedly.

Attempting to rectify any irregularities can only be completed once the cause has been established and, unfortunately, this is not always straightforward.

Causes of irregular periods

  • Age. It is not unusual for a female’s periods to be irregular for the first year or two following puberty. Similarly, periods can become more erratic as a female approaches the menopause.
  • Medical conditions. Polycystic Ovary Syndrome and some thyroid conditions can result in irregular periods.
  • Extreme exercising or dieting. Endurance athletes are prone to irregular menstrual cycles. Similarly, those who are severely underweight are likely to notice a change in their periods; a side effect of excessive weight loss can be complete cessation of menstruation.
  • Stress. Physical or emotional stress can interrupt the menstrual cycle.
  • Birth control. Some forms of hormonal contraceptive, such as the oral contraceptive pill and the mini pill, can result in irregular bleeding.

Having irregular periods is not necessarily a sign that there is something wrong and, in many cases, over time the cycle will regulate itself. However, if you are under 45 years old and your periods suddenly become erratic, it is probably worth consulting your doctor.

Nabta is reshaping women’s healthcare. We support women with their personal health journeys, from everyday wellbeing to the uniquely female experiences of fertility, pregnancy, and menopause

Get in touch if you have any questions about this article or any aspect of women’s health. We’re here for you. 


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