What happens to your hormones during perimenopause

What perimenopause actually is

Perimenopause is the transition phase before menopause itself. The ovaries are gradually winding down but they do not do this neatly.

When it happens

Perimenopause typically starts in the early to mid forties and lasts 4 to 10 years. Some women experience earlier onset, sometimes called premature ovarian insufficiency if it happens before 40. The average age of menopause in the UK is 51, so most women spend the bulk of their forties in perimenopause without necessarily realising it.

Why it is hard to identify

Early perimenopausal symptoms are subtle and easily attributed to stress, ageing, work pressure or anything else. Many women only realise in retrospect that they were in perimenopause for several years before they made the connection. Blood tests are not particularly useful for diagnosis because hormone levels fluctuate so widely. Symptoms plus age remain the best diagnostic approach.

What is happening biologically

The ovaries are running out of viable eggs. The remaining eggs are less responsive to the hormonal signals from the brain. The whole feedback loop that runs the menstrual cycle becomes unstable. The brain compensates by sending stronger signals, which produces hormonal spikes. The result is unpredictable cycles with unpredictable hormone levels.

The end point

Menopause itself is defined as 12 consecutive months without a period. Once that point is reached, the perimenopausal phase ends and the postmenopausal phase begins. Some symptoms improve after menopause. Others develop. The hormonal turbulence settles eventually but the underlying low oestrogen state continues.

What each hormone is doing

The specific hormonal patterns of perimenopause explain why symptoms can be so confusing. Different hormones behave differently as the ovaries decline.

Oestrogen swings wildly

Contrary to the simple narrative, oestrogen does not just fall during perimenopause. It swings. Some cycles produce normal or even higher than normal oestrogen levels. Others produce very low levels. The week to week and month to month variation is extreme. This is why women report symptoms that come and go unpredictably. The high oestrogen weeks can produce different symptoms than the low ones. The variation itself is also a problem because the body has trouble adjusting.

Progesterone drops earlier

Progesterone production typically declines earlier in perimenopause than oestrogen. This is because progesterone is made after ovulation and ovulation becomes less reliable. When ovulation does not happen in a cycle, no progesterone is produced. The result is cycles dominated by oestrogen without the balancing effect of progesterone. This contributes to heavier periods, breast tenderness, mood symptoms and sleep disruption.

FSH rises and rises

FSH (follicle stimulating hormone) is the brain's signal to the ovaries to develop eggs. As the ovaries become less responsive the brain shouts louder by sending more FSH. FSH levels rise progressively through perimenopause. High FSH can be detected on blood tests but levels still fluctuate, so a single test is not diagnostic. Consistently very high FSH alongside absent periods indicates menopause has been reached.

Testosterone declines

Female testosterone levels gradually decline from the thirties onward, with a steeper drop around menopause. This is often overlooked in discussions of perimenopause but contributes to changes in libido, energy and muscle mass. Testosterone is not just a male hormone. Women produce smaller amounts but the effects of decline are real.

Making sense of the chaos

The unpredictable nature of perimenopausal symptoms confuses women who expect a steady decline. The hormonal pattern explains why no two weeks feel the same.

Some weeks are fine

Many women have weeks in perimenopause where everything feels normal. Cycles run on time. Energy is good. Sleep is fine. Mood is steady. This is often a cycle where ovulation happened and hormones did their usual thing. Then the next cycle is different. The variability is the defining feature of perimenopause. The fact that you feel fine one month does not mean perimenopause is over.

The high oestrogen weeks

When oestrogen spikes high in perimenopause it can produce symptoms including heavy periods, breast tenderness, bloating, heavy moods and migraines. These are often interpreted as worsening PMS. They can also be quite different from the woman's previous PMS pattern. Cycles where oestrogen runs high without normal progesterone production particularly produce these symptoms.

The low oestrogen weeks

Low oestrogen produces a different symptom pattern including hot flushes, night sweats, sleep disruption, brain fog, anxiety, joint aches and vaginal dryness. These are the classic menopausal symptoms but they often start years before menopause itself. Women who only know the classic symptom list may not recognise high oestrogen symptoms as part of the same process.

Why mood is so affected

The brain is sensitive to oestrogen fluctuations. Rapidly changing oestrogen produces real mood effects through its influence on neurotransmitters including serotonin. Anxiety, low mood and emotional sensitivity are very common in perimenopause. The effect is biological rather than psychological. Women with previous PMS or postnatal depression are at higher risk of perimenopausal mood symptoms.

Managing the hormonal chaos

Effective help exists for perimenopausal symptoms. The choices depend on the severity of symptoms, personal preference and individual circumstances. Speaking to a GP gets you informed about your options.

HRT for many women

Hormone replacement therapy adds back the oestrogen (and progesterone if needed) that is becoming unreliable. For women in perimenopause, HRT can stabilise the hormonal fluctuations that drive most symptoms. UK guidance has moved toward earlier and more accessible HRT prescribing. The benefits and risks vary by individual. Speak to your GP about whether HRT might suit you.

Beyond HRT

Antidepressants can help with hot flushes and mood symptoms for women who cannot or do not want HRT. Other non hormonal options exist for specific symptoms. Cognitive behavioural therapy has evidence for hot flushes and sleep problems. The treatment landscape is broader than just HRT.

Lifestyle support

Regular strength training, walking, reducing alcohol, prioritising sleep, eating well and managing stress all support perimenopausal wellbeing. None of these fully replace medical treatment when symptoms are significant but they support overall health. They also work alongside HRT or other treatments rather than instead of them.

Track your symptoms

Keeping a record of cycle dates, symptoms and patterns over several months gives you and your GP useful information. The variability is hard to capture in memory. Tracking apps designed for perimenopause are available. Knowing your own pattern helps with treatment decisions and gives you context when symptoms feel overwhelming. Speak to your GP if symptoms are affecting your life.

More on female health

For the full perimenopause picture our Perimenopause: A Complete Guide covers everything in depth. How to Spot the Early Signs of Perimenopause covers the start of the transition. And Hormone Replacement Therapy: A Complete Guide covers the most effective treatment.