Irregular Periods: What Is Normal and What Is Not
Irregular periods is a single phrase covering several quite different problems. Cycles that come too far apart, cycles that stopped altogether, bleeding that is far too heavy, and bleeding that arrives at unpredictable times are not variations of one condition — they have different causes, need different tests and are treated differently.
Sorting out which one is happening does most of the diagnostic work, and it is something a woman can largely do herself before any appointment.
📏 Start with what normal actually is, because the twenty-eight-day cycle is a average rather than a rule. A cycle anywhere from 24 to 38 days is normal, measured from the first day of one period to the day before the next. Bleeding lasting up to eight days is normal. What matters more than the length is the consistency — across a year, the difference between a woman’s shortest and longest cycle should be under about a week. A steady 33-day cycle is entirely normal. A cycle that swings between 24 and 45 days is worth looking into even though both those numbers appear in the normal range.
🗂️ The words, so you can read your own notes
| Term | Meaning |
|---|---|
| Oligomenorrhoea | Infrequent periods — cycles longer than 38 days, or fewer than nine periods a year |
| Secondary amenorrhoea | Periods stopping for three months in someone previously regular, or six months if previously irregular |
| Primary amenorrhoea | Periods never having started by around fifteen, or by thirteen with no other signs of puberty |
| Heavy menstrual bleeding | Blood loss interfering with physical, emotional or social quality of life. Defined by impact rather than by volume |
| Intermenstrual bleeding | Bleeding between periods |
| Postcoital bleeding | Bleeding after sex |
| Postmenopausal bleeding | Any bleeding more than a year after periods stopped. Never normal |
Two periods of life are naturally irregular and do not necessarily indicate a problem. In the first year or two after periods begin, ovulation is often not yet reliable and cycles are erratic. In the years approaching the menopause the same happens in reverse, with cycles typically shortening first and then becoming widely spaced.
🧭 Two families of cause
The modern way of organising this separates causes into those involving a physical abnormality of the uterus and those that do not, because the two need different investigation.
| Structural — something in the uterus | Non-structural — everything else |
|---|---|
| Polyps — small growths of the lining, often causing bleeding between periods | Ovulation problems — by far the commonest group, covering PCOS, thyroid disease, raised prolactin, stress and low body weight |
| Adenomyosis — lining tissue growing into the muscle wall, causing heavy and painful periods and a bulky uterus | Bleeding and clotting disorders — underdiagnosed, particularly where periods have been heavy since they began |
| Fibroids — benign muscle growths; those bulging into the cavity cause the heaviest bleeding | Problems of the lining itself, without any visible abnormality |
| Cancer or precancerous change of the lining — uncommon and the reason certain symptoms are investigated promptly | Medication — hormonal contraception, blood thinners, some psychiatric drugs, an intrauterine device |
An ultrasound largely settles the left-hand column. Blood tests and history cover most of the right.
🥚 The commonest reason cycles are infrequent
Polycystic ovary syndrome is the most frequent cause of infrequent or absent periods in women of reproductive age, and it is more often a hormonal and metabolic condition than an ovarian one, despite the name.
Diagnosis requires two of three features: infrequent or absent ovulation, signs of raised male-type hormones — unwanted hair growth, acne, hair thinning at the scalp, or raised levels on testing — and a characteristic ovarian appearance on ultrasound. Other causes have to be excluded first, and the scan is not needed at all when the other two are clearly present.
The name causes real confusion. The follicles seen on the scan are not cysts in the usual sense; they are eggs that started to develop and stalled. Many women with the condition have entirely normal-looking ovaries, and many women with that ovarian appearance do not have the syndrome.
⚠️ Prolonged absence of periods in PCOS is not simply an inconvenience. Without ovulation there is no progesterone, so the lining of the uterus is exposed to oestrogen with nothing to oppose it. Over years that can lead to thickening of the lining and, in a minority, to precancerous change. This is why a woman going many months without a period is generally advised to have a bleed induced periodically — usually with a course of a progestogen — even when she has no wish to conceive and is not troubled by the absence itself. It is the lining that is being protected, not the cycle.
🍽️ The cause that gets congratulated
When the body detects that energy intake is insufficient for energy being spent, it switches off reproduction as a non-essential function. The signal from the brain to the ovaries becomes irregular and then stops, oestrogen falls, and periods become infrequent and then absent.
This happens with under-eating, heavy exercise, rapid weight loss, low body weight, or sustained psychological stress — and crucially, with any combination of those that produces a shortfall. It does not require an eating disorder and it does not require being visibly thin. A woman who has increased her training substantially while eating the same amount can develop it at an entirely ordinary body weight.
What makes it easy to miss is that it often arrives alongside things people are pleased about — more running, better discipline about food, a smaller size. Periods stopping is frequently treated as a convenient side effect rather than a signal.
It is not harmless. Low oestrogen sustained over months to years causes bone loss that may not be fully recoverable, and stress fractures in athletes are a common way it comes to light. It also affects cardiovascular health and fertility.
The treatment is to correct the energy shortfall — eating more, training less, or both — and periods usually return. Putting a woman on the contraceptive pill instead produces a monthly bleed that looks like recovery, does not restore the underlying signalling, and does not reliably protect bone. It is worth knowing that, because the bleed is reassuring and the reassurance is false.
🦋 The hormonal causes worth excluding
Thyroid disease in either direction disturbs cycles — an underactive thyroid typically producing heavier or more frequent bleeding, an overactive one lighter or absent periods. It is a single blood test and it is frequently the answer.
Raised prolactin, the hormone of breastfeeding, suppresses ovulation. Outside pregnancy and breastfeeding it can come from a small benign pituitary growth, from an underactive thyroid, or from medication — antipsychotics are the commonest culprit, and some antidepressants and antinausea drugs also raise it. The characteristic accompanying sign is milky nipple discharge, though it is often absent. It is treatable, and a persistently raised level warrants finding out why rather than simply regulating the bleeding.
Poorly controlled diabetes, coeliac disease and untreated chronic illness all disturb cycles.
⏳ When it happens early
Periods becoming infrequent and then stopping before the age of forty, with hot flushes, night sweats, vaginal dryness and poor sleep, suggests the ovaries are running out of eggs early. It affects around one in a hundred women under forty and considerably more under forty-five.
Two things about it are frequently handled badly.
It is not the same as infertility — ovarian function can fluctuate and spontaneous pregnancy occurs in a small proportion of women after the diagnosis, which matters both for those hoping to conceive and for those who assume contraception is no longer needed.
And it requires hormone replacement, generally until around the average age of the menopause. This is not the same decision as hormone therapy at the usual menopausal age. A woman of thirty-two facing decades without oestrogen is at real risk of osteoporosis and cardiovascular disease, and replacement here is restoring what her body would normally be producing. Being told to simply manage the symptoms is inadequate advice, and the article on bone health and the menopause covers why.
🩸 Heavy bleeding, measured usefully
Nobody measures menstrual blood loss, so the useful definition is based on effect rather than volume. Bleeding is heavy if any of the following applies.
- Changing protection every hour or two for several consecutive hours
- Needing two forms of protection at once
- Getting up at night to change
- Clots larger than a coin
- Flooding through onto clothes or bedding
- Planning your life around your period — avoiding work, travel or social occasions
- Symptoms of iron deficiency alongside
That last one is the most consequential and the most overlooked.
🩸 Heavy periods are among the commonest causes of iron deficiency in women, and the deficiency arrives long before anaemia does. Haemoglobin can be entirely normal while iron stores are exhausted, so a normal full blood count does not exclude it — ferritin must be checked specifically. Depleted iron causes fatigue, breathlessness on stairs, poor concentration, hair loss, restless legs at night, brittle nails and sometimes a craving to chew ice. Enormous numbers of women live with this for years, attribute it to being busy, and are told their blood count is fine. If your periods are heavy, ask for ferritin by name.
One further point about heavy bleeding: if it has been heavy since the very first period, an inherited bleeding disorder is a genuine possibility and is substantially underdiagnosed in women. Supporting clues are frequent nosebleeds, easy bruising, prolonged bleeding after dental work or surgery, heavy bleeding after childbirth, or a family history. It is worth raising directly, because the question is rarely asked.
🚩 The patterns that need prompt attention
Most menstrual irregularity is not sinister. These particular patterns are the exceptions and should not be watched and waited on.
| Symptom | Why |
|---|---|
| Any bleeding more than a year after the menopause | Never normal at any volume, including a single episode of spotting. Investigated urgently, because cancer of the lining is the diagnosis to exclude and is highly curable when found early |
| Bleeding after sex | Needs examination of the cervix |
| Persistent bleeding between periods | Polyps, cervical problems, infection or lining abnormality |
| New heavy bleeding with pelvic pain and bloating | Needs examination and a scan |
| Any bleeding while pregnant | Assess promptly |
| Severe pain with bleeding and feeling faint | Emergency, particularly where pregnancy is possible |
🔬 What testing is worth doing
A pregnancy test comes first, always, in anyone of reproductive age whose periods have stopped or become irregular, regardless of what contraception is being used and regardless of how unlikely it seems. It is the single commonest cause of periods stopping and skipping it wastes months.
Beyond that: full blood count and ferritin, thyroid function, prolactin, and hormone levels taken early in the cycle where the cycle is long enough to have an early part. Testosterone where there are signs of raised male-type hormones. A pelvic ultrasound covers the structural causes.
Where the question is specifically whether ovulation is occurring, a progesterone level taken about seven days before the next period is expected answers it — which in a long or unpredictable cycle means the timing has to be worked out rather than defaulting to day twenty-one.
Assessment of the lining of the uterus, by a biopsy taken in clinic or by direct inspection with a camera, is done where there is postmenopausal bleeding, persistent bleeding between periods, bleeding that has not responded to treatment, or particular risk factors including long periods without any bleed. The older approach of scraping the lining blind has largely been replaced by looking directly and sampling what is seen, which is both more accurate and less invasive.
💊 Treatment follows the cause and the plan
Two questions determine the approach: what is causing it, and whether pregnancy is wanted now, later, or not at all.
| Situation | Usual approach |
|---|---|
| Infrequent periods, no pregnancy wanted | A progestogen taken cyclically to bring on a regular bleed and protect the lining, or combined hormonal contraception |
| Heavy bleeding, no structural cause | A hormone-releasing intrauterine device is the most effective option; also anti-fibrinolytic tablets during bleeding, anti-inflammatories, or hormonal treatment |
| PCOS, no pregnancy wanted | Cycle regulation as above, attention to weight and insulin resistance where relevant |
| PCOS, pregnancy wanted | Ovulation induction. Letrozole has largely overtaken clomiphene as first choice on effectiveness |
| Low energy availability | Restore intake and reduce training. Hormones do not fix the cause and mask the marker |
| Raised prolactin | Treat the cause; a dopamine agonist where a pituitary cause is confirmed |
| Thyroid disease | Correct the thyroid and cycles usually follow |
| Early ovarian insufficiency | Hormone replacement until around the usual age of the menopause |
| Fibroids, polyps, adenomyosis | Medical or procedural treatment depending on size, position and whether fertility is wanted |
About the progestogens
These are the mainstay for restoring a regular bleed where ovulation is not happening. Given for a set number of days each month, they build up the lining and then, on stopping, allow it to shed — producing a predictable bleed and preventing the lining thickening unopposed.
Two are commonly used and they are not interchangeable. Dydrogesterone is structurally close to natural progesterone, does not suppress ovulation at the usual doses, has no male-hormone-like effects, and is generally well tolerated. Medroxyprogesterone is considerably cheaper and effective for the same purpose, with a somewhat higher rate of side effects such as bloating and mood change in some women. The price difference between them reflects a real difference in the molecule rather than the same drug at two prices.
💡 What the pill does and does not do. Combined hormonal contraception produces a very regular monthly bleed, and that bleed is not a period — it is a withdrawal bleed caused by stopping the hormones for a few days, and it happens whether or not the underlying cycle is functioning. The pill therefore controls the symptom without treating the cause. That is a perfectly reasonable thing to want, and it becomes a problem in two situations: when it is used to make an unexplained irregularity look normal instead of investigating it, and when a woman comes off it years later, finds the original pattern exactly as it was, and is told the pill caused it. It did not; it was concealing it.
📱 Keeping a record that is worth bringing
Three or four months of simple tracking transforms an appointment.
Record the first day of each period, which is what cycle length is counted from. Record how many days you bleed, and how heavy in concrete terms — how many changes, whether there were large clots, whether you flooded. Note any bleeding outside a period, including light spotting. Note anything that changed around when the problem started: weight, training, stress, a new medication, an illness.
Apps do this well enough, and their cycle predictions are guesses rather than measurements — useful for record-keeping, not for contraception.
🩺 When to seek advice
- No period for three months, once pregnancy is excluded
- Cycles consistently shorter than 24 days or longer than 38
- A cycle that swings by more than about a week between shortest and longest
- Bleeding lasting more than eight days
- Heavy bleeding by the practical definition above, particularly with tiredness
- Bleeding between periods or after sex
- Any bleeding after the menopause — promptly, however small
- Periods stopping after increasing exercise or losing weight
- Periods becoming irregular before forty, with flushes or night sweats
- Milky nipple discharge outside pregnancy or breastfeeding
- Unwanted hair growth, acne or scalp hair thinning with irregular cycles
- Trying to conceive for a year, or six months if over thirty-five
Treatment is stocked in the womens health category, including Duphaston (dydrogesterone 10 mg) and Provera (medroxyprogesterone) for cycle regulation, Dostinex (cabergoline) where prolactin is the cause, and Femara (letrozole) and Clomid (clomiphene) for ovulation induction. Which applies depends entirely on the cause, which is why the tests come first.
❓ Frequently asked questions
Is a 33-day cycle abnormal?
No. Anywhere from 24 to 38 days is normal, and twenty-eight is an average rather than a target. What matters more than the length is consistency — across a year, the gap between your shortest and longest cycle should be under about a week. A steady 33-day cycle is fine. A cycle swinging between 24 and 45 days is worth investigating even though both numbers sit inside the normal range.
How do I know if my periods are actually heavy?
By effect rather than volume, since nobody measures it. Changing protection every hour or two for several hours, needing two forms at once, getting up at night to change, clots larger than a coin, flooding onto clothes or bedding, or planning your life around your period all count. So does having symptoms of iron deficiency alongside, which is the most overlooked sign.
My blood count was normal. Can I still be iron deficient?
Yes, and this catches out enormous numbers of women. Iron stores are depleted long before haemoglobin falls, so a normal full blood count does not exclude deficiency — ferritin has to be checked specifically. Depleted iron causes fatigue, breathlessness on stairs, poor concentration, hair loss, restless legs at night, brittle nails and sometimes a craving to chew ice. Ask for ferritin by name.
My periods stopped after I started running more. Is that a problem?
Yes, and it is often congratulated rather than investigated. When energy intake falls short of what is being spent, the body switches off reproduction. It does not require an eating disorder or being visibly thin — increasing training while eating the same amount is enough. Sustained low oestrogen causes bone loss that may not fully recover, and stress fractures are a common way it is discovered.
Why should I bring on a bleed if I am not trying to conceive?
To protect the lining of the uterus. Without ovulation there is no progesterone, so the lining is exposed to oestrogen with nothing opposing it, and over years that can cause thickening and in a minority precancerous change. That is why a woman going many months without a period is usually advised to have one induced periodically, typically with a course of a progestogen. It is the lining being protected rather than the cycle.
Does the pill fix irregular periods?
It controls them without treating the cause. The monthly bleed on combined contraception is a withdrawal bleed from stopping the hormones for a few days, not a period, and it happens whether or not the underlying cycle works. That is a reasonable thing to want. It becomes a problem when it is used to make an unexplained irregularity look normal instead of investigating it, or when someone stops years later and blames the pill for a pattern it was concealing.
Do I have PCOS if my ovaries look polycystic?
Not necessarily. Diagnosis needs two of three features — infrequent or absent ovulation, signs of raised male-type hormones, and the characteristic ovarian appearance — with other causes excluded. Many women with that appearance do not have the syndrome, and many women with the syndrome have normal-looking ovaries. The follicles are not cysts in the usual sense but eggs that started developing and stalled.
What if I bleed after the menopause?
Get it assessed promptly. Any bleeding more than a year after periods stopped is never normal, at any volume, including a single episode of light spotting. Most causes turn out to be benign, and cancer of the lining of the uterus is the diagnosis being excluded — it is highly curable when found early, which is exactly why the rule about not waiting exists.
My periods have been heavy since they started. Does that mean anything?
It raises the possibility of an inherited bleeding disorder, which is substantially underdiagnosed in women. Supporting clues are frequent nosebleeds, easy bruising, prolonged bleeding after dental work or surgery, heavy bleeding after childbirth, or a family history. It is worth raising directly, because the question is rarely asked and the answer changes how the bleeding is managed.
Duphaston and Provera are both progestogens. Which one?
They are different molecules rather than the same drug at two prices. Dydrogesterone is structurally close to natural progesterone, does not suppress ovulation at usual doses, has no male-hormone-like effects and is generally well tolerated. Medroxyprogesterone is considerably cheaper and effective for the same purpose, with a somewhat higher rate of bloating and mood change in some women. The price gap reflects a genuine difference.
When should progesterone be tested to check I am ovulating?
About seven days before the next period is expected, which is not automatically day twenty-one. Day twenty-one only works for a twenty-eight-day cycle. In a long or unpredictable cycle the timing has to be calculated backwards from the expected period, and a test done at the wrong point produces a low result that looks like failure to ovulate when nothing is wrong.
My periods stopped in my thirties. Is that early menopause?
Possibly, and it needs proper assessment rather than symptom management. Two points are often handled badly. It is not the same as infertility — ovarian function can fluctuate and spontaneous pregnancy occurs in a small proportion, which matters for contraception as well as conception. And it generally requires hormone replacement until around the usual age of the menopause, because decades without oestrogen carries real bone and cardiovascular risk.
📑 Sources and editorial
- FIGO definitions of normal and abnormal uterine bleeding and the PALM-COEIN classification
- NICE guideline on heavy menstrual bleeding, assessment and management
- International evidence-based guideline for the assessment and management of polycystic ovary syndrome
- Endocrine Society clinical practice guideline on functional hypothalamic amenorrhoea
- ESHRE guidance on premature ovarian insufficiency and hormone replacement
- Literature on inherited bleeding disorders in women with heavy menstrual bleeding
- Evidence on iron deficiency without anaemia and the role of ferritin testing
- Guidance on investigation of postmenopausal and intermenstrual bleeding
- Trials comparing letrozole and clomiphene for ovulation induction in PCOS
- Prescribing information for dydrogesterone, medroxyprogesterone, cabergoline, letrozole and clomiphene
- Related reading: period pain, osteoporosis and the menopause
- Related products: womens health category
- RXshop Editorial Team — reviewed by Anita Sharma, MD, FACOG, Obstetrician-Gynecologist and Womens Health
Medical Disclaimer: The information in this article is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek guidance from a qualified healthcare provider with any questions you may have regarding a medical condition, and before starting, stopping or changing any medication.