Some women find their menstrual cycle isn't always regular. Their periods may be early or late. They may vary in how long they last or how heavy they are each time.
Causes of irregular periods
Your menstrual cycle can be disturbed if you:
- change your method of contraception
- 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:
- extreme weight loss or weight gain
- too much exercise
An intrauterine system (IUS - progesterone-releasing coil) or contraceptive pill may cause spotting between periods.
An intrauterine device (IUD - coil) ) doesn't cause irregular periods, but can cause heavy bleeding or painful bleeding.
Small bleeds are known as breakthrough bleeds. They are common when the contraceptive pill is first used. They're usually lighter and shorter than normal periods. They usually stop within the first few months.
Polycystic ovary syndrome
Polycystic ovary syndrome (PCOS) occurs when very small cysts (small, fluid-filled sacs) develop in the ovaries.
The usual symptoms of PCOS are irregular or light periods or no periods at all. This is because, in women with PCOS, ovulation (the release of an egg) may not take place as often as normal.
Irregular bleeding can also be caused by:
- an unsuspected pregnancy
- early miscarriage
- 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 is found in the neck.
Your GP may test for a thyroid problem by taking a blood test to check levels of thyroid hormones in your blood.
When to see your GP
Treatment for irregular periods may not always be necessary. You should see your GP if:
- you have bleeding or spotting between periods or after sex
- you have very heavy periods, where you need to change your tampon or pad every hour or two, or you have to wear both a pad and a tampon
- you experience heavy bleeding that floods into your bed or through your clothes
- your periods last longer than seven days
- your periods are more frequent than once a month
You may need a different contraceptive, or further investigations may be needed to find out whether you have an underlying health condition.
The average menstrual cycle
About the menstrual cycle:
- on average, a woman's menstrual cycle lasts 28 days
- 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
More useful links
- Heavy periods
- Absent periods
- Painful periods
- Irregular periods
- How to use your health services
The information on this page has been adapted from original content from the NHS website.
For further information see terms and conditions.