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Why are some women's periods irregular?

Dr Louisa Draper

"Most young women get their first period between the ages of 10 and 15, but this varies between individuals. When you first start having periods, you may notice that your cycle is different each month for the first couple of years. "

Dr Louisa Draper

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Once women have been through puberty, they usually develop a regular menstrual cycle with periods that occur around the same time each month. Women’s menstrual cycles last on average 28 days, but can vary from woman to woman. 

However, there are many reasons why some women may experience irregular periods. Some women find that they have periods early or late in their menstrual cycle; that they may last longer or shorter than usual, or that they may sometimes be heavy and sometimes lighter. 

Hormonal changes can affect your periods. If you are using hormonal contraception (such as the pill, the mini-pill, contraceptive patches, contraceptive injections or the contraceptive coil), and you change the method that you normally use, this can affect your menstrual cycle. Also, if you have an imbalance of the female sex hormones progesterone and oestrogen, this can also make your periods irregular. Women with polycystic ovary syndrome (PCOS) can also experience irregular periods.

Other reasons for hormonal changes which can affect the regularity of your periods include losing a lot of weight or exercising too much. Stress and anxiety can also induce hormonal changes which can cause irregular periods. When the stress hormone cortisol is released by the body, it can have a direct effect on the levels of oestrogen and progesterone, which can change the timing of your menstrual cycle.