Irregular periods: causes and which hormones to test

One month your period arrives on day 24, the next not until day 40, and sometimes it simply stays away. Your app has not predicted anything accurate for months. An irregular period is usually not a disease in itself, but a signal that something is shifting somewhere in your hormone balance. The cause often lies with your thyroid, with PCOS, with stress or with a transition in your life.

This is the overview article of our cycle series. My take: a single off month says little, but a pattern that has persisted for half a year deserves attention. Six hormones together usually give the first direction: FSH, LH, TSH, prolactin, estradiol and progesterone. Below you read when a cycle is truly irregular, which causes often play a part, which hormones give insight and when a test can be worthwhile.

When is a period irregular?

A cycle is called irregular when the time between two periods varies greatly, is structurally shorter than 21 days or longer than 35 days, or when you menstruate fewer than eight times a year. A single off month simply belongs to it and is usually no reason for concern. According to Thuisarts.nl and the NHG, variation within roughly 21 to 35 days is normal.

A normal cycle lasts on average 28 days, but anything between roughly 21 and 35 days is within the margin. So it is not about one number, but about your own pattern.

• The cycle varies greatly in length each month
• You menstruate fewer than eight times a year
• Your period stays away for months without being pregnant
• Intermittent blood loss that keeps returning

Which causes often play a part?

The cause ranges from a thyroid that works too slowly or too fast, to PCOS, a raised prolactin, stress, severe weight loss or the approaching menopause. Which cause fits you depends on your age, your other complaints and your history.

• Thyroid problem: an underactive or overactive thyroid can disrupt your cycle
• PCOS: one of the most common hormonal causes, often with acne or hair growth
• Raised prolactin: can inhibit ovulation and suppress the period
• Stress and weight: heavy weight loss, intensive exercise or prolonged stress can shut down the cycle
• Perimenopause: around menopause the cycle often becomes more erratic

Some of these causes call for a targeted approach, others resolve on their own as the underlying situation improves. Suspect PCOS? Then read our PCOS pillar on symptoms, causes and diagnosis.

Which hormones give insight?

No single hormone points to the cause on its own, but a fixed set of hormones together often brings a pattern into view. The table below links each symptom to a possible cause and to the value that usually says the most about it.

The best moment to draw blood depends on what you want to know. FSH, LH and estradiol are usually measured in the first days of your cycle (day 2 to 5), progesterone around day 21. If you have no or a very irregular period, blood can be drawn at any time.

The Women's Hormones panel measures FSH, LH, estradiol and prolactin, among others, in one draw, so you get the whole pattern into view rather than one isolated number. This table is a tool, not a diagnosis. If you are unsure whether your progesterone fits your cycle phase, compare it with our progesterone reference values per cycle phase.

What if the cause is PCOS?

PCOS is one of the most common hormonal causes of an irregular cycle. It is estimated that roughly 1 in 10 women have it, and a large share do not know. The picture often combines an erratic cycle with acne, hair growth or difficulty conceiving.

With PCOS, besides FSH and LH you also look at testosterone and SHBG. A raised LH/FSH ratio with signs of too many androgens often fits the picture, although no single value proves PCOS alone. Want to understand more deeply how your cycle works day to day? Then read understanding your menstrual cycle and the hormones.

Why the timing of the draw matters so much

Your cycle is not a flat line, but a wave. In the first half (the follicular phase) an egg follicle matures and your estradiol rises. Around ovulation LH peaks briefly, and in the second half (the luteal phase) progesterone takes the lead role. As a result, the same value says something very different depending on the day you draw blood.

A few rules of thumb that help in practice:

• FSH, LH and estradiol: usually day 2 to 5, because then you see the baseline without the peak around ovulation
• Progesterone: around day 21 in a 28-day cycle, to see whether ovulation has happened
• Prolactin and TSH: less cycle-dependent, although prolactin is preferably drawn in the morning and rested
• No or a very erratic cycle: then blood can be drawn at any time, because there is no fixed day to align with

If you draw on the wrong day, a normal value can still look abnormal, or the other way around. That is one of the reasons why a single result without context is hard to place. At Lunara every value therefore gets an explanation of what it can mean at that moment in your cycle.

Irregular by life stage: what belongs and what does not

Whether an irregular cycle is worrying depends strongly on your life stage. A pattern that is completely ordinary at seventeen can be a reason to look at thirty. It helps to place your own situation in that context before you worry, or before you let something slide.

• Around puberty: in the first years after your first period an erratic cycle is very common, because ovulation does not yet happen every month.
• After the pill: when you stop hormonal contraception it can take several months for your own cycle to return. If it stays away after half a year, a check is worthwhile.
• After a pregnancy or during breastfeeding: the cycle often only gets going again later, and that is usually normal.
• From your late thirties and forties: around perimenopause the cycle becomes erratic again, with varying lengths and sometimes heavier or lighter blood loss.

What applies in all these stages: a single off month need not mean anything, but a pattern that persists for months and comes with other complaints deserves attention. Unsure which stage you are in and what fits it? Then a conversation with your GP, possibly with a hormone picture alongside, is a logical first step.

Track your own cycle before you test

One of the most useful things you can do yourself costs nothing: track your cycle for a few months. A doctor can do much more with "my cycle has been swinging between 24 and 45 days for four months" than with "it feels irregular". It makes your story concrete, and it helps to choose the right moment for any test.

What is handy to note down:

• The first day of each period, so you see the length between cycles
• How heavy your blood loss is and how long it lasts
• Accompanying complaints such as acne, hair growth, hot flushes or mood swings
• Changes in stress, weight, sleep or exercise intensity

With that data a result is easier to place, because your hormones only tell a story when you know which day and which complaints they belong to. An app or simply a notepad both work fine. Take this information to your GP or add it, in your mind, to what your result shows.

When an absent period needs more attention

An irregular cycle is different from a period that stays away entirely. If your period stays away for three months or longer and you are not pregnant, doctors call this amenorrhoea, and that deserves investigation. The cause ranges from prolonged stress and heavy weight loss to a thyroid problem or a raised prolactin.

The combination of an absent period with intensive exercise, eating little or heavy weight loss in particular is a signal to take seriously. Prolonged low estrogen levels can affect your bones over time, something the Health Council of the Netherlands (Gezondheidsraad) also notes in the context of bone health in women. If you recognise this, discuss it with your GP rather than waiting.

Irregular cycle and trying to conceive

An erratic cycle makes predicting your fertile days difficult, which complicates timing conception. It does not automatically mean you cannot conceive. Many women with an irregular cycle do conceive, sometimes spontaneously and sometimes with help.

Want to map your hormones before you start? The Fertility Assessment looks at AMH, FSH and LH, among others. Also read which blood test is worthwhile when trying to conceive. Always discuss a result with a doctor, as the NVOG (Dutch Society of Obstetrics and Gynaecology) and international guidelines stress that the result can only be placed together with your symptoms.

When is testing worthwhile?

A test is mainly worthwhile when a pattern has persisted for a while or when several complaints come together. A single late month rarely calls for action. A cycle that has been erratic for half a year, or complaints that affect your daily life, do.

• Your cycle has been irregular for more than six months
• Your period stays away for months without pregnancy
• Alongside cycle complaints you also have fatigue, acne or hair growth
• You are trying to conceive and your cycle is unpredictable

An abnormal result is not a diagnosis on its own. So always discuss your results with your GP, who can place the whole picture.

Testing your cycle via Lunara: how it works

You do not need a referral from the GP for a hormone test. You order online, schedule an appointment at a draw location near you and have blood taken in the morning. You receive your result digitally, usually within a few working days.

Every result gets context from a BIG-registered doctor, per value. So you not only know what your FSH or TSH is, but also what that can mean in your situation. Mainly bothered by PMS complaints in the second half of your cycle? Then read about PMS complaints and what helps. Is your period very heavy instead? Then read about heavy periods and when to test.

Frequently asked questions

How long may my cycle deviate before I take action?

A single off month is normal. If your cycle is structurally shorter than 21 or longer than 35 days, or if the pattern has been erratic for half a year, a check can be worthwhile. If in doubt, discuss it with your GP.

Which hormones to test with an irregular cycle?

You often start with FSH, LH, TSH, prolactin, estradiol and progesterone. Together they give insight into the thyroid, ovulation and possible causes such as PCOS. No single value makes a diagnosis alone.

Can stress disrupt my period?

Yes, it can. Prolonged stress, heavy weight loss or intensive exercise can inhibit ovulation and temporarily shut down the cycle. The cycle often recovers as the underlying situation improves, but have persistent complaints assessed.

Sources

• NHG guideline on vaginal blood loss, Dutch College of General Practitioners. Available via richtlijnen.nhg.org.
• Thuisarts.nl, I have an irregular period, Dutch College of General Practitioners. Available via thuisarts.nl.
• NVOG (Dutch Society of Obstetrics and Gynaecology), patient information on cycle and fertility. Available via degynaecoloog.nl.

Every blood test result via Lunara receives a professional review by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.