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Irregular Periods

Why are some women's periods irregular?

Irregular Periods

Why are some women's periods irregular?

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.

Last reviewed: 13/12/2019 by Dr Simran Deo

Irregular periods during puberty

Most young women get their first period (known as the ‘menarche’) 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 after menarche. 

Girls going through puberty sometimes skip a period or get an extra bleed during their menstrual cycle. It is also not uncommon for periods during puberty to differ. While some periods may last for as few as a couple of days, other periods may be heavier and last for a week.

If you are sexually active and have recently had unprotected sex, a missed period could be a sign of pregnancy. If this applies to you, see you doctor, who will check whether you are pregnant.

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Periods during the menopause

The time before menopause is known as ‘perimenopause’ and during this time hormone levels, particularly oestrogen, go up and down. This occurs around four years before the actual menopause (the time of your final period) and can affect the regularity of your periods. 

Some perimenopausal woman may not have periods for months, or they may experience spotting between periods. Some may notice much lighter, or much heavier periods. The menstrual cycle may last for a shorter time than usual, or a longer time. All of this is caused by the fluctuations in hormone levels caused by the arrival of the menopause.

If you experience extremely heavy bleeding during the perimenopause, it is important to visit your doctor to rule out other conditions, such as fibroids, endometriosis, or more serious conditions that can sometimes be mistaken for menopausal symptoms.

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Medications which can affect your periods

There are a number of medicines that can affect how regular your periods are. These include:

  • Hormonal contraceptives - including the combined contraceptive pill, the mini-pill, contraceptive injections, contraceptive implants, intrauterine system (IUS), and the coil.
  • Anticoagulants (medicines used to thin the blood) - aspirin and warfarin and other blood thinners.
  • NSAIDs (non-steroidal anti-inflammatory drugs) - for example, ibuprofen.
  • Chemotherapy - used to treat cancer.
  • Thyroid medications.
  • Hormone therapy - for example, hormone replacement therapy (HRT).

If you are taking any of these medicines and are experiencing irregular periods, talk to your doctor. 

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Which other factors can affect the regularity of your monthly bleeding?

Other reasons for irregularity in your periods include:

  • excessive exercise
  • being very underweight
  • eating disorders
  • thyroid gland disorders
  • an excess of a hormone called androgen
  • endometriosis
  • fibroids
  • diabetes

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When to see a doctor

If your menstrual cycle is usually regular and you suddenly experience irregular periods for no apparent reason, visit your doctor. If you have recently had unprotected sex and your period is late, it could mean that you are pregnant. You should take a pregnancy test. 

If the test is negative and you’ve missed two or three periods, see your doctor. You missing periods could be due to hormonal changes which may need treatment. 

If you are bleeding between periods or after sex, have very heavy periods, or have periods that last longer than seven days, see your doctor.

These symptoms could be due to an infection, problems with your cervix, or rarely, cancer.

If you are under the age of 45 and your periods have stopped, or if you are over 65 and are still experiencing bleeds, seek medical help. 

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Available treatments

In most cases, irregular periods will settle without treatment.

Sometimes a change in lifestyle, such as dealing with stress you may be experiencing, exercising more gently or eating a balanced diet may be all that’s needed to restore your normal menstrual cycle. 

However, if your irregular periods become a problem or if you are experiencing additional symptoms see a doctor, who will be able to decide on the best course of treatment for you. 

In many cases, irregular periods can be treated with hormonal medications such as oral contraceptives or an intrauterine device (IUD) that help to balance your hormone levels.

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