What causes it?
“Abnormal uterine bleeding isn’t a diagnosis in itself, it’s a term that describes a symptom, not the cause,” says Dr Ann. There can be lots of different reasons behind it, including hormone changes, sexually transmitted infections, and conditions including endometriosis and PCOS, and, less commonly, conditions such as cervical, uterine or ovarian cancer.
When the bleeding happens can often give important clues about what might be causing it.
Bleeding after menopause
It’s pretty normal to have irregular bleeding during perimenopause – the time leading up to your final period, when your hormones are changing. But once you’ve been through menopause – usually when you’re over 45 and you’ve gone at least 1 year without a period – bleeding is less common.
- it may be caused by things that aren’t serious, including inflammation and thinning of your womb due to low estrogen
- polyps (usually non-cancerous growths) of the cervix or womb
- sometimes, HRT can cause breakthrough bleeding, especially when you first start using it
- in rare cases, it can be a sign of ovarian cancer or womb cancer
Check any bleeding after menopause with your healthcare professional, even if it’s a one-off.
Bleeding during or after sex
There can be a lot of different causes for bleeding after or during sex (you may not notice the blood until afterwards), but it should be investigated by a medical professional. It may happen during any kind of vaginal penetration, not just penis-in-vagina sex. Some possible causes are:
- things that are uncomfortable but not dangerous, like friction, vaginal dryness and lack of lubrication
- things that need treatment, like pelvic inflammatory disease or sexually transmitted diseases such as chlamydia
- Issues with your cervix, like polyps (usually non-cancerous growths) or cervical ectropian
- in rare cases, more serious causes such as cervical or uterine cancer
Bleeding during pregnancy
Seeing blood when you’re pregnant is always alarming. But in fact, it’s common in early pregnancy, happening in up to 1 in 4 pregnancies, and doesn’t always mean there’s a problem with the pregnancy. It can happen simply because more blood vessels have developed in your cervix, so it bleeds more easily. You may notice this after sex, for example.
However, always get checked out because it can be a sign of more worrying causes such as:
Bleeding in later pregnancy can be serious and you should always seek help urgently.
Bleeding after first-time sex
This can happen if your hymen – a thin piece of skin partially covering the entrance of your vagina – tears or stretches the first time you have sex.
- it doesn’t always happen, though – your hymen can tear or break before that, during exercise or from using tampons, for example
- the amount of blood may be so small you may not notice
Heavy periods
You have heavy periods if you feel bleeding has gotten heavier than usual, and/or if any of the following happen:
- blood soaks through to your clothes or your bedsheets
- you have to have to change your tampon or sanitary towels very regularly, such as every 1-2 hours
- you pass large clots – the size of a quarter, or bigger
- you have to double up on sanitary products
- your period lasts more than 7 days
- you have to avoid work or your hobbies because of your periods
- you have to get up in the night to change sanitary protection
Around 1 in 3 women report heavy menstrual bleeding at some point, but that doesn’t mean it’s normal.
- it can be caused by conditions including endometriosis, where womb tissue grows outside your womb, pelvic inflammatory disease, fibroids or polyps
- if you don’t release an egg (ovulate) regularly, womb lining can get thicker and build up, which can result in heavy bleeding when the womb lining sheds. It’s more common around puberty and perimenopause, and can happen in women with PCOS or an underactive thyroid
- problems with your blood that stops it from clotting, such as liver disease or inherited clotting disorders, can make you bleed more
- some medicines, like blood thinners and aspirin, can cause heavy bleeding in some women
- heavy periods can also be associated with diabetes and kidney problems
- the IUD can cause it, especially in the first year you start using it
- what seems like a heavy period could be a miscarriage or ectopic pregnancy (you may not have known you were pregnant)
- and, less commonly, it can be a sign of cervical cancer or endometrial cancer, although endometrial cancer tends to affect women after the menopause and in their 60s
Random vaginal bleeding
Bleeding between periods can range from light to heavy, happen once or regularly, and it can have a number of different causes, but should always be checked out. These can include:
- starting on hormonal contraception like the combined pill, progesterone-only pill, patch, implant, injection or IUS – these can all cause irregular bleeding in the first few months
- HRT may also sometimes cause unpredictable bleeding or spotting, especially when you first start on it
- missing a contraceptive pill, or being sick soon after taking one, so you haven’t absorbed the hormones
- taking emergency contraception or ‘the morning after pill’
- hormone changes due to perimenopause or PCOS
- a recent miscarriage or abortion
- STIs like chlamydia
- fibroids
- harmless changes in your cervix, or vaginal dryness
- cervical or womb polyps
- less common, serious causes like vaginal, vulval, cervical or uterine cancer
Bleeding for a month straight
Everyone’s periods are different, but if you have one that goes on for more than 7 days, it could be a sign of a problem and should be investigated. Some women may bleed for up to a month. Again, there can be a lot of potential reasons, including:
- conditions such as fibroids, uterine polyps (small benign growths in your womb), endometriosis and adenomyosis (where bits of the womb lining get into your womb’s muscle layers)
- hormonal imbalances like hypothyroidism
- bleeding disorders
- hormone changes in perimenopause can also cause longer, irregular periods
- more rarely, conditions like cervical or uterine cancer
Is abnormal uterine bleeding ever serious?
Usually, it’s nothing to worry about, or is caused by something like an infection, which often can easily be treated. But there can be more serious causes and complications:
- it may be a sign of miscarriage or ectopic pregnancy
- if you lose a lot of blood, whatever the underlying cause, you may become anemic or even go into shock
- rarely, it could be a symptom of a type of cancer that affects your reproductive organs, such as vaginal, cervical, uterine or ovarian cancer
- that’s why it’s always important to seek emergency help for very heavy bleeding
- if you have unusual bleeding and pain, or if the bleeding is less heavy and irregular, to be checked by a doctor, even if you don’t think there’s anything to worry about. They can rule out serious causes
“Always get unusual bleeding and other symptoms checked”
Sally was diagnosed with cervical cancer after having unusual vaginal bleeding. “I was having some unusual bleeding between periods and after sex, as well as a few urine infections. I’ve always attended smear tests and wasn’t due another until the following year,” she says on the Jo’s Cervical Cancer Trust website. After treatment, Sally is now free of cancer, but says: “If you’re experiencing bleeding, like I was, then a smear test isn’t what you need. In fact, it will just slow everything down! I wanted to share my story to urge others to get any unusual symptoms, like bleeding, checked.”