Irregular Periods: Common Causes, the Right Tests and When to Act

What is a normal cycle and when does irregularity become a problem?

A normal menstrual cycle lasts between 21 and 35 days, measured from the first day of one period to the first day of the next. Normal bleeding lasts between three and seven days. Cycles that consistently fall outside these ranges, or that have changed noticeably from your previous pattern, are worth looking into.

Complete absence of periods is called amenorrhoea (Amenorrhoea). Primary amenorrhoea means periods have never started by age 15 to 16. Secondary amenorrhoea means periods that were happening have now stopped for three months or more in a woman who previously had regular cycles, or six months in one who was already irregular. Infrequent periods, less often than every 35 days, is called oligomenorrhoea (Oligomenorrhoea).

One or two delayed cycles in a year without obvious cause are common and usually not a sign of anything serious. A persistent pattern over three months or more is the point at which investigation is helpful, because a regular period is one of the best signs that the hormonal system is in balance.

PCOS: the most common hormonal reason for irregular periods

Polycystic Ovary Syndrome (PCOS) is the most common hormonal cause of irregular periods in women of reproductive age worldwide. It is characterised by elevated androgens (male-type hormones), irregular or absent ovulation, and often, though not always, multiple small follicles visible on the ovaries during ultrasound.

A 2023 study in Annals of African Medicine found that women with PCOS showed notable imbalances in LH and FSH levels compared with unaffected women, which directly explains why ovulation becomes irregular. Without reliable ovulation, the hormonal cycle that drives a regular period does not complete properly, and bleeding becomes unpredictable.

Symptoms beyond irregular periods include unwanted hair growth on the face, chest or abdomen, persistent acne that does not respond well to standard treatment, difficulty losing weight or unexplained weight gain, and sometimes darkening of the skin in skin folds at the neck or armpits. Any combination of these with irregular periods makes PCOS a strong possibility worth testing for.

A 2024 case-control study published in BMC Women's Health, examining Palestinian women with PCOS, found that those with the condition experienced significantly worse premenstrual symptoms and poorer overall psychological wellbeing than unaffected women. This reinforces that PCOS is not only a hormonal problem but one that affects daily quality of life in ways that extend well beyond the calendar.

Thyroid disease and periods: a connection many women miss

Thyroid hormones play a direct role in regulating the menstrual cycle. A 2023 review published in the International Journal of Molecular Sciences examined the relationship between thyroid function and female reproduction in detail. Hypothyroidism, an underactive thyroid, tends to cause heavy and frequent bleeding in some women, while hyperthyroidism, an overactive thyroid, more often causes light, infrequent or absent periods.

A 2024 study of 304 premenopausal women referred for oligomenorrhoea found that thyroid disorders were among the most prominent endocrine causes identified. A single TSH blood test is sufficient to rule this in or out, and it is one of the cheapest and most widely available blood tests in the region.

The challenge is that the symptoms of hypothyroidism, fatigue, weight gain and feeling cold, are easily attributed to lifestyle or stress, meaning years can pass without diagnosis. If your periods have become irregular alongside any of these symptoms, a thyroid test should be among the first things you check.

Elevated prolactin: a common cause that is frequently overlooked

Prolactin (Prolactin) is the hormone that stimulates milk production after delivery, but it can rise abnormally in women who are not pregnant or breastfeeding, and when it does, it disrupts the hormonal signals needed for ovulation and regular periods. A 2020 narrative review in the International Journal of Endocrinology and Metabolism identified hyperprolactinaemia as one of the key endocrine causes of menstrual disturbance.

Causes of elevated prolactin include: a small benign tumour in the pituitary gland called a prolactinoma (Prolactinoma), certain medications including some antihypertensives, antipsychotics and gastric medications, hypothyroidism, and sometimes intense physical or emotional stress. Occasionally no clear cause is found.

Associated symptoms worth watching for include milky discharge from the nipple without pregnancy or breastfeeding, headaches behind the eyes, and in rare cases of a larger tumour, visual disturbances. The prolactin blood test is widely available and straightforward. It should ideally be taken in the morning before physical activity or a stressful commute, as both can temporarily raise the level.

Stress, weight and intense exercise: functional causes that stop periods

The menstrual cycle is remarkably sensitive to the body's overall energy state and psychological load. Severe and sustained psychological stress, significant and rapid weight loss, and prolonged intensive exercise can all suppress the hypothalamus in the brain, which then reduces or stops its hormonal signals to the pituitary and ovaries. The result is irregular or absent periods without any underlying structural disease.

The Endocrine Society's 2017 clinical practice guideline on functional hypothalamic amenorrhoea (Functional Hypothalamic Amenorrhoea) defines this condition precisely and notes that it is reversible once the triggering factor is addressed. Weight restoration, a reduction in exercise intensity, and psychological support are the main treatments, not hormonal medication.

This pattern may be particularly common across much of our region, where economic hardship, conflict and displacement add chronic stress loads that are not captured in Western epidemiological studies. Young women in contexts of food insecurity who are simultaneously restricting intake and exercising to manage stress are especially vulnerable to this pattern.

Which blood tests should you ask for?

The standard starting panel for irregular periods includes TSH to rule out thyroid disease, prolactin to rule out hyperprolactinaemia, FSH and LH to assess the signals from the brain to the ovaries, and anti-Mullerian hormone (AMH) which reflects ovarian reserve and is elevated in PCOS. If there are symptoms of excess androgens, such as hair growth or persistent acne, total testosterone and DHEA-S are added.

If PCOS is suspected, fasting glucose and fasting insulin are valuable because a significant proportion of women with PCOS have insulin resistance, even without a formal diabetes diagnosis. Identifying this changes the treatment approach and has long-term health implications.

A pelvic ultrasound, either through the abdomen or transvaginally, completes the initial picture by showing the size and appearance of the ovaries and any structural changes to the uterus. For assessing PCOS, it should ideally be performed on days two to five of the cycle if a period is present.

Other causes worth considering

The approach to perimenopause, the transition phase before menopause, typically begins in the mid-forties and causes increasingly irregular cycles with changes in flow and frequency. An elevated FSH combined with low oestradiol confirms this stage. Knowing this is the cause changes the conversation from investigation to management and symptom support.

Structural causes including uterine polyps (Polyps) and fibroids (Fibroids) can change the pattern and quantity of bleeding without necessarily disrupting the cycle length. These are not identified by hormonal blood tests but by ultrasound or hysteroscopy, and they are common enough to be worth considering alongside hormonal causes.

Medications are a routinely missed cause of cycle changes. Antihypertensives, antipsychotics, antiepileptics, and hormonal treatments can all affect cycle regularity. If your periods changed after starting a new medication, mention this to your doctor specifically, because a dose adjustment or alternative drug often resolves the problem without further investigation.

When does irregular bleeding need urgent attention?

Most menstrual irregularity does not constitute an emergency, but certain patterns should prompt a faster medical assessment. In any sexually active woman, absent periods require a pregnancy test first, because an ectopic pregnancy (Ectopic Pregnancy) can present as a missed period with pelvic pain, and this is a genuine surgical emergency.

Very heavy bleeding that soaks more than one large pad per hour for two or more consecutive hours, or bleeding that continues without stopping beyond seven days, deserves prompt evaluation to identify hormonal, structural or clotting causes. This is not a pattern to manage at home with iron tablets alone.

Sudden severe pelvic pain alongside a missed or late period is a red flag for ectopic pregnancy or ovarian torsion. Both require urgent hospital assessment and should not be treated with watchful waiting at home.

What to expect at your doctor's appointment and what comes next

Your doctor will begin with a detailed history: how long has the irregularity been happening, did it start at the same time as a change in your weight, a new medication, or a period of significant stress? Has your period disappeared entirely or simply become less frequent? Are there accompanying symptoms such as headache, nipple discharge, hair growth or acne?

The answers to these questions direct the testing from the start and avoid unnecessary investigations. Arriving at the appointment with a list of your last several period dates, your current medications and any supplements you are taking will save time and help your doctor build the right picture quickly.

Treatment after diagnosis depends on the cause. PCOS is managed with lifestyle modification, sometimes medications that restore ovulation, and hormonal treatment to regulate the cycle if pregnancy is not the immediate goal. Thyroid disorders are treated with medication that, in most cases, restores cycle regularity within a few months. Elevated prolactin responds very well to dopamine agonist drugs. Functional hypothalamic amenorrhoea requires addressing the root cause, whether that is nutrition, exercise load or psychological support, rather than hormonal prescription.

Whatever the cause, the key point is that irregular periods are not simply a cosmetic inconvenience. They reflect something in the body's hormonal regulation that is not working as it should, and identifying and treating that cause has benefits that extend well beyond cycle regularity.

A gynaecologist or endocrinologist with experience in reproductive hormones is the right specialist for this evaluation. In settings where specialist access is limited, a general practitioner can order the initial panel of blood tests and refer based on results. The testing itself does not require a specialist.

Sources

• Saei Ghare Naz M, Rostami Dovom M, Ramezani Tehrani F et al: The Menstrual Disturbances in Endocrine Disorders: A Narrative Review, International journal of endocrinology and metabolism, 2020
• Brown EDL, Obeng-Gyasi B, Hall JE et al: The Thyroid Hormone Axis and Female Reproduction, International journal of molecular sciences, 2023
• Yilmaz H, Demirpence M, Belet U et al: Prevalence of endocrine disorders in 304 premenopausal women referred with oligomenorrhoea, Endokrynologia Polska, 2024
• Almahareeq M, Hamdan M, Vanoh D et al: Comparison of premenstrual symptoms, psychological well-being, and nutritional status between Palestinian women with and without polycystic ovarian syndrome: a case-control study, BMC women's health, 2024
• Gordon CM, Ackerman KE, Berga SL et al: Functional Hypothalamic Amenorrhea: An Endocrine Society Clinical Practice Guideline, The Journal of clinical endocrinology and metabolism, 2017
• Awwad O, Saleh M, Bardaweel S et al: Use of complementary and alternative medicine among females with polycystic ovary syndrome in Jordan: a cross-sectional study, BMJ open, 2024
• Kambale T, Sawaimul KD, Prakash S et al: A study of hormonal and anthropometric parameters in polycystic ovarian syndrome, Annals of African medicine, 2023