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There are many causes for bleeding between periods, usually it is not serious but it should always be investigated. Bleeding that occurs at different times each cycle may be more serious. 

Treatment of bleeding between periods

We plan treatment depending on the underlying cause of the bleeding. Where we find no cause, we can treat the bleeding between periods with cyclical hormones.

What will happen during your visit?

We first ask about your health. This is to understand what factors are most likely to be causing the heavy periods.

A gentle pelvic examination is undertaken. This allows us to look at the vagina and cervix carefully. You may need swabs from the vagina to check for infections and we will often do a smear test.

We may need to examine the cervix with a colposcope. This is a detailed examination of the cervix with magnification.

We will usually arrange a pelvic ultrasound. This shows the inside of the uterus and the ovaries to check for causes of the bleeding between periods.

We take blood tests to look at the hormone balance. Blood tests also look for other causes of abnormal bleeding.

Causes for bleeding between periods

Hormone imbalance
The most common cause of bleeding between periods is a hormone imbalance. Estrogen and Progesterone are the two hormones that control the lining of the uterus.

Estrogen makes the lining of the uterus thicken up. This happens in the first half of the cycle.

Progesterone counteracts this stimulation. Progesterone is dominant in the second half of the cycle. It matures the endometrium ready for the egg to implant if conception has occurred.

Just before the period starts the level of estrogen and progesterone both fall. This causes the endometrium to break down and produces a period.

The balance between estrogen and progesterone is delicate. Any change in this balance can cause abnormal bleeding between periods.



Oral contraception is often responsible for bleeding between periods. We call bleeding between periods for women on the pill breakthrough bleeding.

Combined oral contraceptive (COC) pills contain both estrogen and progesterone. This is usually in a fixed ratio. Sometimes the balance between these hormones in any individual pill isn’t right for you.

If you experience breakthrough bleeding, a change of pill may control the bleeding.

Many women run packets of the pill together so that they only have a period every two or three months. This is safe and may work well. It does increase the chance of breakthrough bleeding.

The minipill often causes irregular bleeding and bleeding between periods.

Spotting between periods is very common in the first few months of use of the Mirena coil. Usually the bleeding will stop without treatment after 6 to 8 weeks.

Stress can cause abnormal bleeding between periods. The pituitary gland is at the base of the brain. It produces FSH (follicle stimulating hormone) and LH (luteinising hormone). These control the amount of estrogen and progesterone produced by the ovary.

Emotional events can have an effect on the release of FSH and LH. This can cause abnormal bleeding between periods.

Many women spot briefly in the middle of their cycle at the time of ovulation. This is often associated with a little pain. We call this pain mittelschmerz, which is German for “middle pain”.

This type of spotting is regular in timing, and usually occurs around day 14 of a 28-day cycle. If your cycle is longer than 28 days, the mid-cycle bleeding may occur a little later.

Uterine polyps
Polyps may develop inside the uterus. These polyps are almost always benign, but can cause troublesome bleeding between periods. An ultrasound scan will diagnose polyps. We can remove these with a minor procedure.

Vaginal Infections
Some vaginal infections, particularly sexually transmitted ones can cause abnormal bleeding between periods. Pelvic inflammatory disease is also associated with abnormal bleeding.

Early pregnancy complications

Abnormal bleeding between periods can be the result of an unrecognised early preganancy. This could be the sign of an early miscarriage or an ectopic pregnancy.

Ovarian cysts

Many ovarian cysts produce estrogen. The extra estrogen can disrupt the normal hormone balance. leading to abnormal bleeding between periods. Many of these cysts will be physiological. They will resolve without treatment. We will need to remove other cysts.

Steroid injections

Steroid injections can cause abnormal bleeding between periods. The anti-inflammatory steroid in the injection can cross react with ovarian hormones.

The injected steroid can disrupt the hormone balance and cause vaginal bleeding.


Cancers are the most serious cause of bleeding between periods. These are uncommon causes of bleeding between periods. The cancers that can cause abnormal bleeding are:

  • Cervix

  • Uterus

  • Ovary

  • Vagina

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