Irregular cycles are a symptom, not a diagnosis. Finding the underlying cause is what makes the difference between managing symptoms and actually getting better.
By Dr. Neha Sain · Gynaecologist, MS (Obstetrics & Gynaecology)
"My periods are all over the place" is one of the most common things I hear in my clinic. And I want to be clear about something upfront: an irregular cycle is never something to simply accept and manage around. It is your body's way of telling you that something in the underlying hormonal system is not working correctly. Finding out what that something is — and addressing it — is almost always possible.
Let me walk you through the eight causes I encounter most frequently, and what the investigation and treatment of each actually looks like.
First: what counts as irregular?
A normal menstrual cycle is 21–35 days from the first day of one period to the first day of the next. A period lasting 2–7 days with moderate flow — roughly 30–80 ml total — is typical. If your cycle is consistently shorter than 21 days, longer than 35 days, wildly variable from month to month, or if you are having fewer than eight periods a year, your cycle is irregular by clinical definition.
Occasional variation — a cycle that is a few days longer during an exam period, or slightly shorter when you travel — is normal. Sustained unpredictability is not.
1. PCOS — the most common cause in reproductive age
Polycystic Ovary Syndrome is the single most frequent cause of irregular periods in women of reproductive age, affecting approximately 1 in 5 Indian women according to the ICMR-PCOS National Task Force. In PCOS, elevated LH and insulin levels disrupt the normal hormonal cascade that produces ovulation. Without regular ovulation, periods become infrequent, unpredictable, or absent.
The irregular period is often accompanied by other signs: acne (particularly on the jaw and chin), excess hair on the face, neck, or abdomen (hirsutism), hair thinning on the scalp, and difficulty losing weight despite effort. Not every woman with PCOS has all of these — some have only the menstrual irregularity.
Investigation: pelvic ultrasound plus blood tests — FSH, LH, AMH, testosterone, fasting insulin, and a thyroid function test (because thyroid disease frequently coexists and must be ruled out). A 2-hour glucose tolerance test is important because insulin resistance is present in 50–70% of Indian women with PCOS.
2. Thyroid disease — underdiagnosed and very common in India
India has one of the highest burdens of thyroid disease globally, and thyroid dysfunction is one of the most frequent causes of menstrual irregularity that I see. Both hypothyroidism (underactive) and hyperthyroidism (overactive) disrupt the hormonal signals that regulate the cycle.
With hypothyroidism, periods tend to be heavy and more frequent — sometimes occurring every two to three weeks — and are often accompanied by fatigue that goes far beyond tiredness, cold intolerance, constipation, weight gain, hair fall, and a slowed heart rate. With hyperthyroidism, periods tend to become light and infrequent, and are accompanied by weight loss, a rapid heartbeat, heat intolerance, anxiety, and tremor.
Investigation: TSH and Free T4. A single blood test. Treatment is straightforward and highly effective — and cycle regularity often returns within two to three months of starting thyroid medication.
3. Stress — its effect on the hormonal axis is real and underestimated
I want to be precise here, because "your periods are off because of stress" is advice that is sometimes given dismissively, as though the solution is simply to worry less. The mechanism is real and specific.
The hypothalamus — the brain region that initiates the hormonal cascade leading to ovulation — is profoundly sensitive to cortisol, the primary stress hormone. In periods of sustained psychological or physical stress, cortisol suppresses the pulsatile release of GnRH (gonadotropin-releasing hormone), which in turn suppresses LH and FSH, which means ovulation does not occur, which means the period either does not come or comes late.
I see this pattern most commonly in women going through exam periods, grief, major relationship changes, or periods of overwork combined with under-sleeping and under-eating. The cycle irregularity is not imaginary — it is a physiological consequence of a measurably elevated cortisol state.
The investigation is largely about ruling out other causes. Treatment is the stress itself — which I recognise is not simple advice. What I can offer is the reassurance that when the stressor lifts, or when adequate support is put in place, the cycle almost always normalises within one to two months.
4. Weight changes — in both directions
Significant weight changes in either direction disrupt menstrual regularity, and the mechanisms differ.
With significant weight gain, oestrogen is produced by adipose (fat) tissue in addition to the ovaries. This excess oestrogen disrupts the feedback loops that regulate the cycle and, in women with underlying PCOS, worsens the already-elevated insulin and androgen environment.
With significant weight loss — whether from intentional dieting, extreme exercise, illness, or an eating disorder — the body interprets energy deficiency as a threat. The hypothalamus, reading inadequate fuel as famine, suppresses the reproductive axis as an energy-conservation measure. This is called hypothalamic amenorrhoea, and it produces absent periods that can persist for months or years.
I want to be clear that hypothalamic amenorrhoea is not the same as PCOS. The ultrasound, the AMH, the androgen levels — all are different. Treatment is not hormonal contraception or metformin; it is nutritional rehabilitation, sometimes alongside psychological support if there is a disordered eating component.
5. Hyperprolactinaemia — elevated prolactin outside of breastfeeding
Prolactin is the hormone that stimulates milk production. Outside of pregnancy and breastfeeding, high prolactin levels suppress GnRH in exactly the same way that stress cortisol does — resulting in infrequent or absent ovulation and irregular periods.
The most common cause of elevated prolactin outside breastfeeding is a prolactinoma — a small, benign tumour of the pituitary gland that produces prolactin autonomously. Prolactinomas are far more common than most women realise, and the vast majority are microadenomas (under 10mm) that cause no structural problems and respond extremely well to medication.
Other causes include certain medications — particularly antipsychotic medications, metoclopramide (Maxolon, commonly used for nausea), and some antidepressants.
The distinguishing symptom is galactorrhoea — milky discharge from the nipple in a woman who is not pregnant or breastfeeding. This is not always present, but when it is, it is a strong pointer. Investigation: a single blood test for prolactin. If elevated, MRI of the pituitary. Treatment with cabergoline or bromocriptine is highly effective.
6. Perimenopause — which can begin earlier than expected
Perimenopause — the transition period leading to menopause — is typically discussed as something that happens in the late forties. In reality, hormonal fluctuations associated with declining ovarian reserve can begin in the early forties, and occasionally in the late thirties.
In perimenopause, oestrogen levels fluctuate unpredictably rather than declining smoothly. This produces cycles that become increasingly variable — sometimes longer, sometimes shorter, sometimes heavier, sometimes lighter — before eventually stopping. This variability can last four to eight years.
Investigation: FSH and oestradiol blood tests, ideally on day 2–3 of the cycle. AMH (anti-Müllerian hormone) gives an indication of remaining ovarian reserve. In a woman over 40 with new-onset cycle irregularity and symptoms like hot flushes, night sweats, or mood changes, perimenopause is high on my differential.
7. Endometriosis and adenomyosis
Both endometriosis (endometrial tissue outside the uterus) and adenomyosis (endometrial tissue within the uterine muscle) can produce heavy, irregular bleeding rather than simply painful regular periods. The cycle in these conditions is often irregular in volume and duration rather than in timing — periods may come on time but last ten or twelve days with very heavy flow.
The distinguishing feature is pain — severe, worsening period pain, pain during sex, pain with bowel movements during periods, chronic pelvic pain. If your periods are irregular and painful — particularly if the pain is worsening over years — please do not accept "painful periods are normal" as an answer. They are not.
8. After stopping hormonal contraception
After stopping the combined oral contraceptive pill, some women experience a delay of several months before their natural cycle resumes — called post-pill amenorrhoea. In most cases, the cycle returns within three to six months. If it has not returned within six months, investigation is appropriate — because the pill can mask underlying conditions like PCOS or thyroid disease, which now become apparent.
When to see me
If any of the above resonates with your experience, a gynaecological consultation is the right next step. I see patients through Smart Consultation — you can share a detailed account of your cycle history, your symptoms, and any tests you have already had, and I will give you a clear, practical assessment of what I think is happening, what investigations I would recommend, and what the treatment options look like.
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