When Did Perimenopause Actually Start?

There is a moment many women have in their forties where something feels different, but it is difficult to name exactly what that difference is.

You are still cycling. You are still functioning. Life is still full. But something about your body, your mood, or your energy feels unfamiliar.

For me, the timeline has always been slightly blurred.

I had my daughter at forty-one, so the years that followed were a haze of baby brain, broken sleep and the general exhaustion that comes with raising small children. When you are navigating early motherhood in your forties, it is almost impossible to separate what belongs to motherhood and what belongs to hormones or perimenopause

Was the brain fog simply sleep deprivation?

Was the anxiety just the pressure of juggling work and family?

Were the heavier periods simply a random change?

Looking back now, I wonder if something else had already begun.

Because what many of us do not realise is that perimenopause is not one long, gradual transition. It actually has two very different phases, each with its own biology and its own set of experiences.

Understanding that distinction can make the entire journey feel far less confusing.

Perimenopause Is Not One Long Phase

We often speak about perimenopause as though it is one continuous stage that slowly leads to menopause.

But hormonally, it behaves more like two very different chapters.

Early perimenopause is driven by hormonal volatility. Estrogen can spike high and then drop suddenly, while progesterone begins its gradual decline.

Later perimenopause is defined by depletion. Estrogen becomes low more often than high, progesterone is very low, and cycles begin to disappear for longer stretches of time.

As exercise physiologist and women’s health researcher Dr Stacy Sims explains,

“Perimenopause is not a single hormonal environment. Early perimenopause is characterised by fluctuations, while late perimenopause becomes a state of hormonal decline.”

The distinction matters because the body is responding to two very different hormonal landscapes.

Early Perimenopause: The Hormonal Rollercoaster

In early perimenopause many women still have regular cycles, which can make it difficult to recognise that anything is changing.

Ovulation, however, becomes less consistent. Progesterone, the hormone that supports calmness, sleep and emotional stability, is usually the first to decline.

At the same time estrogen begins to fluctuate dramatically. Some days levels are higher than they have ever been. Other days they drop sharply.

This hormonal unpredictability is what creates the rollercoaster many women describe.

Periods may become heavier. PMS may feel far more intense than it once did. Breast tenderness, mood swings and anxiety can appear seemingly out of nowhere.

Dr Stacy Sims often describes this stage as a period of hormonal chaos rather than hormonal loss.

“Early perimenopause is characterised by estrogen swings rather than estrogen deficiency.”

For many women this stage is confusing precisely because estrogen has not disappeared. In fact, at times it can be extremely high. The issue is not absence, but instability.

The Prevention Window

One of the lesser discussed aspects of early perimenopause is that it also represents a powerful opportunity.

During this stage the body is still producing estrogen, which continues to provide important protection for bone density, cardiovascular health and brain function.

This means lifestyle interventions can have a particularly strong impact. Prioritising sleep, managing stress, building strength and supporting metabolic health can significantly influence how the later stages unfold.

Dr Sims frequently emphasises that women in their forties should not approach training the same way they did in their twenties or thirties.

“Women need to shift toward strength training and higher quality recovery as they move through perimenopause.”

This is the stage where building muscle, supporting the nervous system and protecting long term metabolic health become especially important.

The Quiet Signs Many Women Miss

Early perimenopause rarely arrives with a clear announcement.

More often it appears as subtle shifts that are easy to dismiss or attribute to other aspects of life.

Heavier bleeding can gradually deplete iron levels. Thyroid function may begin to shift. Insulin resistance can quietly develop. Mood changes are often attributed to stress or the demands of work and family.

When I look back at my own experience, it is easy to see how those signals could be missed. When you are raising children, building a career and trying to keep life running smoothly, it is natural to assume that fatigue or emotional changes are simply the result of being busy.

For many women, early perimenopause hides in plain sight.

Late Perimenopause: The Drop Zone

Later perimenopause feels very different.

Cycles begin to skip and then return unpredictably. Sometimes they cluster together and then disappear for months at a time.

Estrogen becomes low more frequently than high. Progesterone levels are very low. The body begins to move toward the hormonal landscape of menopause.

This stage is when many of the symptoms most commonly associated with menopause begin to appear.

Hot flashes and night sweats become more common. Sleep can become fragmented or difficult. Brain fog becomes more noticeable. Vaginal dryness and increased nervous system sensitivity may develop.

At the same time the body begins to experience more visible metabolic changes. Bone density declines more rapidly, cholesterol levels can rise and muscle loss accelerates.

This is why strength training becomes so critical during this stage. Maintaining muscle mass is one of the most powerful ways to support metabolic health, bone density and long term vitality.

Same Woman, Different Biology

One of the most reassuring things to understand about perimenopause is that these stages are not signs that something is wrong with your body.

They simply reflect different biological environments.

Early perimenopause is chaotic. Hormones are fluctuating wildly.

Late perimenopause is depleted. Hormones are gradually declining.

The same woman is experiencing both phases, but her body is operating under completely different hormonal conditions.

And once we begin to understand that distinction, the experience becomes far less mysterious.

Instead of feeling as though our bodies are unpredictable or failing us, we can begin to respond with strategies that actually match the biology of the stage we are in.

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