Female Hormone Profile
A six-marker hormone panel measuring oestradiol, progesterone, LH, FSH, testosterone, and SHBG.
£79.00
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Overview
What Is Irregular Periods?
Irregular periods — medically termed oligomenorrhoea (infrequent periods) or amenorrhoea (absent periods) — describe menstrual cycles that deviate significantly from the typical 21–35 day pattern. This includes cycles that are persistently shorter than 21 days, longer than 35 days, absent for more than three months, or highly variable from month to month. Irregular periods are not merely inconvenient — they signal disruption to the hormonal axis that governs ovulation, fertility, and long-term bone and cardiovascular health.
The most common cause of irregular periods in women of reproductive age is polycystic ovary syndrome (PCOS). PCOS is characterised by elevated LH relative to FSH, raised testosterone, and often insulin resistance — all of which prevent the regular follicular development and ovulation that drives a normal cycle. Thyroid disorders are the second most important category: both hypothyroidism and hyperthyroidism disrupt the HPG (hypothalamic-pituitary-gonadal) axis and alter the FSH and LH signals needed to trigger ovulation. A TSH test is therefore essential in any investigation of cycle irregularity.
In women approaching 40, rising FSH and declining oestradiol signal the onset of the perimenopausal transition — a natural process but one that benefits from hormonal clarity. Adrenal dysfunction and chronic stress affect the cycle by suppressing GnRH pulsatility, effectively telling the pituitary to reduce FSH and LH output. Iron deficiency worsens the impact of heavy menstrual bleeding, and elevated HbA1c from insulin resistance directly disrupts ovarian hormone production. Understanding which of these mechanisms is driving irregular periods is the foundation of effective management.
Irregular Periods vs. PCOS
PCOS is the most common cause of irregular periods in women under 40 — accounting for up to 80% of cases of oligomenorrhoea in the reproductive years. However, thyroid dysfunction, hyperprolactinaemia, perimenopause, adrenal disorders, and significant weight change can all produce identical cycle disruption. A PCOS diagnosis should never be made on period irregularity alone — blood tests measuring LH, FSH, testosterone, TSH, and fasting insulin are essential to distinguish PCOS from other hormonal causes and to confirm the diagnosis.
Related experience
Common Symptoms Associated With Irregular Periods
Irregular periods rarely occur in isolation — associated symptoms help narrow down the underlying hormonal cause and guide testing.
Night Sweats
Common in perimenopausal women whose cycles are becoming irregular due to declining oestradiol
Weight Gain
Insulin resistance in PCOS drives both cycle irregularity and progressive weight gain, especially centrally
Fatigue
Hypothyroidism and iron deficiency — both common causes of irregular periods — also produce marked fatigue
Low Libido
Disrupted sex hormone production affects sexual desire alongside cycle regularity
Hair Loss
Androgenic excess in PCOS causes scalp hair thinning alongside cycle disruption
Anxiety
Hormonal fluctuation during perimenopause or cortisol dysregulation drives both cycle changes and anxiety
The big picture
What Causes Irregular Periods?
Irregular periods arise from disruption to several distinct hormonal axes — identifying which is driving the irregularity determines the correct investigation and treatment approach.
What to measure
Biomarkers Associated With Irregular Periods
These are the key blood markers that reveal the hormonal cause of irregular periods and guide clinical management.
LH
Luteinising hormone; elevated LH relative to FSH is characteristic of PCOS; elevated alone suggests perimenopause
FSH
Follicle-stimulating hormone; elevated FSH confirms reduced ovarian reserve; used with LH to characterise cycle disruption
Oestradiol
Low oestradiol alongside high FSH confirms perimenopausal transition; critical for assessing bone-protective hormone levels
Testosterone (Total)
Elevated testosterone in women with irregular periods is the hallmark androgenic marker of PCOS
TSH
Both hypothyroidism and hyperthyroidism disrupt cycle regularity; TSH is the essential first-line thyroid screen
DHEA-S
Elevated DHEA-S indicates excess adrenal androgen production as a contributor to cycle disruption
Ferritin
Iron stores depleted by heavy or frequent periods compound fatigue and should be measured alongside hormones
HbA1c
Insulin resistance, assessed via HbA1c, directly disrupts ovarian hormone production and is central to PCOS management
Underlying causes
Conditions Associated With Irregular Periods
Several diagnosable conditions present with irregular periods as a primary symptom — each has distinct biomarker patterns and treatment pathways.
PCOS
The leading cause of irregular periods in women under 40; driven by elevated androgens, LH excess, and insulin resistance
Hypothyroidism
An underactive thyroid disrupts GnRH and LH pulsatility, causing heavy or infrequent periods
Hyperthyroidism
An overactive thyroid accelerates the HPG axis and typically causes short, frequent, or absent periods
Menopause
The perimenopausal transition produces increasingly irregular, unpredictable cycles before periods cease
Adrenal Dysfunction
Cortisol excess suppresses reproductive hormone signalling, causing cycle irregularity as a secondary effect
Getting answers
How Irregular Periods Is Investigated
A structured approach to hormone testing provides a clear biological explanation for irregular periods in most cases.
1
Time your blood test correctly
Reproductive hormone tests — LH, FSH, and oestradiol — are most informative when taken on days 2–5 of the menstrual cycle (early follicular phase). If your cycle is absent or unpredictable, testing can be done at any time with an explanatory note to your clinician. TSH and HbA1c can be tested at any point in the cycle.
2
Distinguish PCOS from thyroid disorders first
LH, FSH, and testosterone combined with TSH covers the two most common diagnoses. In PCOS, expect LH:FSH ratio greater than 2:1 alongside elevated testosterone. In thyroid disorders, TSH will be abnormal with corresponding free T4 change. These patterns are distinct and direct very different management.
3
Add metabolic markers for PCOS confirmation
HbA1c and fasting glucose identify the insulin resistance present in 70–80% of women with PCOS. DHEA-S helps distinguish adrenal androgen excess from ovarian androgen excess — an important distinction for treatment planning. SHBG is often low in PCOS and amplifies the effect of elevated testosterone.
4
Assess iron and overall nutritional status
Ferritin should be measured in all women with irregular or heavy periods. Iron deficiency worsens fatigue and is common in women with PCOS who experience heavy breakthrough bleeding. Vitamin D deficiency is associated with worsened insulin resistance and should be included in a comprehensive screen.
Recommended testing
Recommended Blood Tests
Private blood tests analysed by UK-accredited laboratories.
Prolactin and Pituitary Check
A targeted three-marker panel measuring prolactin, LH, and FSH to investigate pituitary function, irregular periods.
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Essential Menopause Check
A five-marker menopause panel measuring FSH, LH, oestradiol, testosterone, and SHBG.
£79.00
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Growth Hormone and IGF-1 Panel
A specialist two-marker panel measuring IGF-1 (insulin-like growth factor 1) and IGFBP-3 as stable surrogate markers for growth hormone status.
£149.00
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Comprehensive Hormone and Wellbeing Panel
A 20-marker comprehensive hormone and wellbeing panel covering sex hormones, adrenal markers, thyroid function, metabolic indicators.
£249.00
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Insulin Resistance and Metabolic Hormone Panel
A six-marker metabolic and hormone panel assessing fasting insulin, HbA1c, glucose, cortisol, DHEAS, and adiponectin.
£119.00
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Everyday contributors
Lifestyle Factors That Can Contribute
Alongside targeted blood testing, several evidence-based lifestyle interventions support hormonal regularity and cycle restoration.
Low-Glycaemic Diet
Reducing refined carbohydrates and sugar lowers fasting insulin, directly improving LH and androgen levels in PCOS — the most evidence-based dietary intervention for cycle restoration
Regular Moderate Exercise
30–45 minutes of aerobic exercise five days per week improves insulin sensitivity and reduces the LH-to-FSH imbalance characteristic of PCOS
Healthy Body Weight
Even a 5–10% reduction in weight in women with PCOS and excess weight is sufficient to restore ovulation in many cases, through improved insulin sensitivity
Consistent Sleep
Circadian rhythm disruption alters GnRH pulsatility and menstrual regularity; consistent sleep and wake times support reproductive hormone rhythms
Stress Management
Chronic psychological stress elevates cortisol and suppresses the GnRH pulse generator, disrupting LH and FSH signalling at the source
Vitamin D Supplementation
Vitamin D deficiency worsens insulin resistance in PCOS; supplementation to maintain levels above 75 nmol/L supports both metabolic and reproductive function
Safety first
When To Seek Medical Advice
Most cycle irregularity can be investigated and managed systematically, but certain presentations require prompt medical assessment.
Red flags — speak to a doctor
These can point to a more serious underlying cause and should not be ignored.
- No period for more than three consecutive months (amenorrhoea) in a non-pregnant woman — requires medical assessment to identify the underlying cause and assess bone health implications
- Very heavy or prolonged bleeding (soaking through a pad or tampon every hour, or bleeding lasting more than seven days) — warrants urgent gynaecological review
- Sudden change in cycle length or pattern following previously regular periods, especially if accompanied by weight loss, pain, or other unexplained symptoms
- Significant unintentional weight loss alongside cycle cessation — this combination may indicate a serious underlying condition including eating disorders or systemic illness
Common questions
Frequently Asked Questions
The most common causes of irregular periods are PCOS, hypothyroidism, hyperthyroidism, the perimenopausal transition, and adrenal dysfunction. In young women, PCOS is by far the most common — characterised by elevated LH, raised testosterone, and often insulin resistance. In women over 35, perimenopausal hormonal changes should also be considered. Iron deficiency and significant weight change can also disrupt cycle regularity.
Yes — both hypothyroidism and hyperthyroidism can disrupt the menstrual cycle. An underactive thyroid typically causes heavy, infrequent periods or oligomenorrhoea, while an overactive thyroid may shorten the cycle or cause periods to become very light or absent. TSH testing should be included in every investigation of cycle irregularity, as thyroid disorders are common, treatable, and frequently overlooked in this context.
Not always — some women with PCOS have regular cycles but still have the hormonal and metabolic features of the condition. Conversely, irregular periods can result from many causes other than PCOS. The diagnosis of PCOS requires at least two of three criteria: irregular or absent periods, clinical or biochemical evidence of elevated androgens (such as elevated testosterone), and polycystic ovarian morphology on ultrasound. Blood tests measuring LH, FSH, testosterone, and HbA1c are essential to characterise the condition.
Yes — psychological and physical stress elevates cortisol, which inhibits the GnRH pulse generator in the hypothalamus. This reduces pituitary output of LH and FSH, preventing follicular development and ovulation. The result is delayed, irregular, or absent periods. Very low body weight and excessive exercise have an equivalent effect. A morning cortisol blood test can confirm whether adrenal-driven stress suppression is disrupting your cycle.
A comprehensive investigation should include LH, FSH, and oestradiol (ideally on day 2–5 of the cycle), total testosterone, DHEA-S, TSH, HbA1c, and ferritin. SHBG is a valuable addition as it reflects the biological activity of testosterone and is frequently low in PCOS. Trupoint’s female hormone profile and PCOS hormone screen cover all of these markers in a single private blood test.
Keep exploring
Related Symptoms
Related Biomarkers
Related Conditions
Sources
References
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Teede HJ et al. — View source
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Krassas GE et al. — View source
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Legro RS et al. — View source
This page is for general information only and does not replace personalised medical advice. If you are worried about your health, please speak to a qualified healthcare professional. Trupoint Health blood tests are analysed by UK-accredited laboratories.