Health A to Z
Some women find their menstrual cycle isn't always regular. Their periods may be early or late, and may vary in how long they last or how heavy they are each time.
Your normal menstrual cycle can be disturbed if you change your method of contraception, or if you have an imbalance of the reproductive hormones oestrogen and progesterone.
Many factors can cause a hormone imbalance, from polycystic ovary syndrome (PCOS) to extreme weight loss and excessive exercise.
Read more about the causes of irregular periods.
Treatment for irregular periods may not always be necessary. However, you should see your GP if:
You may need a different contraceptive, or further investigations may be needed to find out whether you have an underlying health condition.
Read more about treating irregular periods.
On average, a woman's menstrual cycle lasts 28 days, but cycles can vary from 24 to 35 days.
After puberty, most women develop a regular menstrual cycle, with around the same length of time between periods.
Menstrual bleeding usually lasts two to seven days, with the average being five days.
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Your menstrual cycle can be disturbed if you change your method of contraception or you have an imbalance of the hormones oestrogen and progesterone.
It's not unusual to have a hormone imbalance for a few years after puberty and before the menopause. This can cause your menstrual cycle to become longer or shorter. Your periods may also become lighter or heavier.
If your irregular periods are caused by these age-related factors, you won't usually need to see your GP.
The following lifestyle factors can also upset your balance of hormones and cause irregular bleeding:
Small bleeds, known as breakthrough bleeds, are common when the contraceptive pill is first used. They're usually lighter and shorter than normal periods, and usually stop within the first few months.
Polycystic ovary syndrome (PCOS) occurs when very small cysts (small, fluid-filled sacs) develop in the ovaries.
The production of hormones may also be unbalanced, and you could have higher levels of testosterone than normal. Testosterone is a male hormone that women usually have a small amount of.
Irregular bleeding can also be caused by an unsuspected pregnancy, early miscarriage, or problems with the womb or ovaries. Your GP may refer you to a gynaecologist (a specialist in conditions of the female reproductive system) if further investigation and treatment is needed.
A thyroid disorder is another possible, but rare, cause of irregular periods. The thyroid gland, found in the neck, produces hormones that maintain the body's metabolism (the chemical processes your body uses to turn food into energy). Your GP may test for a thyroid problem by taking a blood test to check levels of thyroid hormones in your blood.
Treatment for irregular periods isn't always necessary.
For example, hormone changes are common during puberty and can cause changes to the normal menstrual cycle. Treatment during this time isn’t usually needed.
However, you should see your GP if you have any of the following changes in your periods:
Your GP will ask about your periods, lifestyle and medical history to find the underlying reason for your irregular cycle. Any necessary treatment will depend on the reason for your irregular periods.
If you've recently been fitted with an intrauterine device (IUD) and are experiencing irregular bleeding that doesn't settle within a few months, discuss changing to another method of contraception with your GP or practice nurse.
If you have started taking a new contraceptive pill that's causing irregular bleeding, you may be advised to change to another type of pill.
Alternatively, an intrauterine system (IUS) such as Mirena may be recommended. This is a soft, flexible plastic device that's inserted into your womb and releases a small amount of a hormone called progestogen.
Mirena is a very effective method of contraception (over 99%). You can use it for up to five years and it can be removed at any time. After it's removed, your fertility will return to normal and you can try to become pregnant straight away.
As well as being an effective method of contraception, Mirena can be used to treat heavy, irregular periods. Your periods will become lighter, shorter and, in some cases, less painful.
For overweight women with polycystic ovary syndrome (PCOS), the symptoms can be improved by losing weight, which will also help with irregular periods.
By losing weight, your body doesn't need to produce as much insulin, which reduces testosterone levels and improves your chance of ovulation (releasing an egg each month).
Other treatments for PCOS include hormone treatment and diabetes medication. Read more about treating PCOS.
Treatment for thyroid disorders aims to return the level of thyroid hormones in your blood to normal.
You may need to take medication to stop your thyroid gland producing too many hormones, or too few.
Your menstrual cycle should return to normal after treatment. See your GP if it doesn't.