In recent years, the conversation around perimenopause has gained urgency as more women seek answers and support for their symptoms. Perimenopause, the transitional phase leading up to menopause, is marked by fluctuating hormones—especially progesterone and estrogen—along with changes in brain signaling. Unlike the simplified idea that your estrogen is falling in a linear decline, this stage reflects a variable, whole-body transformation that prepares the body and mind for the aging process. If you have been wondering if you are perimenopausal, you’re in the right place.

Yet, despite these profound changes, many women feel dismissed or misunderstood by healthcare providers who may not be fully informed about perimenopause. We’re seeing an increasing amount of research being done on women’s bodies, and we’re learning that they’re more complex and dynamic than we initially thought. 

It’s time for a paradigm shift in how we view perimenopause, moving away from outdated misconceptions toward a more empowering understanding that acknowledges the brain’s role in managing these hormone transitions. By bringing awareness to what’s going on behind the scenes and reframing perimenopause as a phase of growth rather than decline, we can help women navigate their journey with greater clarity, resilience, and confidence.

Your Reproductive Years: Menstrual Phases

To understand the changes that are on the horizon in perimenopause, we have to start with what a normal menstrual cycle looks like. Each egg stored in the ovaries is surrounded by a follicle, which controls the release of some of the hormones that affect your cycle and eventual egg release.

Menstrual Phase (Days 1–5)

This phase marks the beginning of the cycle, where the uterine lining sheds, resulting in menstrual bleeding. Levels of estrogen and progesterone are low during this phase, leading to the breakdown and shedding of the uterine lining. 

Follicular Phase (Days 1–13)

This phase overlaps with the menstrual phase and involves the maturation of ovarian follicles in preparation for ovulation. Follicle-stimulating hormone (FSH) is released by the pituitary gland, stimulating the growth of ovarian follicles. As these follicles mature, they release estrogen, leading to a gradual increase in estrogen levels. 

Ovulation (Day 14)

Ovulation is the release of a mature egg from the ovary, typically occurring mid-cycle. This is accompanied by a big increase in luteinizing hormone (LH), which is triggered by high estrogen levels and prompts ovulation. This LH surge is needed for the release of the egg. 

Luteal Phase (Days 15–28)

Following ovulation, the luteal phase prepares the body for a potential pregnancy. The ruptured follicle transforms into what’s called the “corpus luteum,” which releases progesterone. Elevated progesterone levels thicken the uterine lining, readying the uterus for embryo implantation. If fertilization does not occur, progesterone and estrogen levels decline, leading to your next period and the beginning of your next cycle. 

The Menopausal Transition

Perimenopause is characterized by lots of fluctuations and starts when you begin experiencing disturbances in your cycle length. This starts somewhere in your 40s or 50s and ends in your late 50s. That means that this phase can last a few years or more than 10!

The belief is that your estrogen immediately starts declining when you enter perimenopause, but that’s not exactly true. There are a couple of distinct phases to this transition. 

Late Reproductive Phase

Doctors most often say that the first symptom of perimenopause is cycle unpredictability, but some research suggests that before your cycle timeline starts to become altered, you’ll experience what’s called “flooding menstruation.” This really just means that your periods become very heavy. This is an indicator that you will be entering perimenopause soon. 

During this phase, you’re still getting your period on a semi-regular basis, but your FSH levels will be higher than normal.

Perimenopause

We are going to be breaking perimenopause into two phases, the first when you are still getting a period, albeit unpredictable, and the second when your period stops. Here’s where we’re splitting this phase: 

Perimenopause Part 1: Spiking Estrogen and Falling Progesterone

The beginning of your perimenopausal phase is when your body getting ready to dispose of all of your eggs in your ovaries. This is when you’ll start to experience irregular cycle length. 

FSH causes your egg to be released, which is controlled by another hormone called inhibin. Inhibin keeps your pituitary gland from releasing too much FSH so you don’t run out of eggs early in your life. In an effort to get rid of more eggs, less inhibin is produced, and several follicles are stimulated to release an egg at the same time, which actually spikes your estrogen, not decreases it. This higher level of estrogen is usually coupled with low progesterone, and this combination is what causes those perimenopausal symptoms. 

So now you may be wondering, when do those typical symptoms of night sweats, mood changes, and sleep problems come into the picture? These symptoms are typically an indicator of low estrogen, it’s essentially due to estrogen withdrawal. There’s two times this happens, in perimenopause part 1 and part 2.

Early in perimenopause when you still have your period and your body is still getting rid of eggs, these estrogen withdrawal symptoms pop up when you’re about to have your period because that’s the time in your cycle when estrogen is lowest. Progesterone is also falling at this time because your ovulatory phase is becoming shorter, so that ratio is driving the classic menopause symptoms.  

Perimenopause Part 2: Falling Estrogen and Low Progesterone

Toward the end of perimenopause, after your body is done getting rid of your eggs, your estrogen starts declining to the levels we’re used to seeing after menopause. These levels are far lower than they are during your menstruating years or the beginning of perimenopause. Levels will still cycle throughout the month, but the average amount of estrogen will begin to lower. 

Here’s a visual representation:

Image: Perimenopause: The Ovary’s Frustrating Grand Finale

Perimenopause part 2 is usually when you stop getting your period, and is characterized by a decrease in progesterone production because you are either no longer ovulating. 

This overview is a bit reductionist because there are a lot more hormones at play here, but we will get into that later in our article series when we talk about testing and treatment. 

Menopause

What menopause is can be a common point of confusion, often thought of as an ongoing process or phase rather than what it truly is—a single point in time. Medically, menopause is defined as the moment when a woman has gone 12 months without a menstrual period. 

For most women, this milestone occurs in their fifties, but it varies widely.

Post-Menopause

As you move through menopause, your body becomes more used to the lower amounts of estrogen in your body, and symptoms will subside. But low estrogen levels bring about other changes too. 

What Does Chronically Low Estrogen do to the Body?

Low levels of estrogen cause other changes in your body, but many can be mitigated with the proper strategy. Here are some common changes:

1. Lower bone density: Estrogen helps your body maintain bone density through by facilitating the addition and maintenance of calcium. With lower estrogen, bones become more porous and fragile, increasing the risk of fractures.
2. Thinning and dry skin: Estrogen is also related to collagen and moisture levels in your body. Lower estrogen levels thin skin and make it harder to retain moisture. 
3. Increased risk of heart disease: Estrogen helps keep blood vessels flexible and promotes healthy cholesterol levels, so lower estrogen makes your blood vessels more stiff and prone to buildup. 
4. Mood swings: Estrogen has a complex relationship with mood regulation, and its decline can contribute to mood swings, anxiety, and sometimes depression.
5. Weight gain around your midsection: Estrogen helps regulate body fat distribution. Lower levels can lead to increased fat storage around your stomach and overall weight gain.
6. Muscle loss: Estrogen helps protect muscle fibers. Lower estrogen levels lead to faster degradation of muscle fibers, causing muscle weakness. Estrogen also supports muscle building from protein and without it, the body struggles to build and repair muscle tissue.

While these changes can be a lot to adjust to, menopause and the years that follow are often a time of empowerment and personal growth. As the body stabilizes, many women feel liberated from the monthly cycle and can instead focus on personal goals and health.

Understanding the effects of low estrogen can help you make proactive choices and, if necessary, seek treatment to support bone health, cardiovascular function, and overall well-being. 

Want to Learn More?

In our next installment, we will talk about how you can mitigate some of these changes to support your body throughout this process and why menopause isn’t a bad thing! Menopause can be a positive life transition that allows women to step into a new and equally important role in their lives. 

References 

1. Prior JC. “Clearing Confusion About Perimenopause.” BC Medical Journal. https://bcmj.org/articles/clearing-confusion-about-perimenopause
2. Centre for Menstrual Cycle and Ovulation Research. “Perimenopause: The Ovary’s Frustrating Grand Finale.” https://www.cemcor.ubc.ca/resources/perimenopause-ovary%E2%80%99s-frustrating-grand-finale
3. Briden L. “The Real Reason Stress Hits Hard in Your 40s: Adrenal Health.” Lara Briden’s Blog. https://www.larabriden.com/real-reason-stress-hits-hard-in-your-40s-adrenal/
4. Cleveland Clinic. “Low Estrogen: Symptoms and Causes.” https://my.clevelandclinic.org/health/diseases/22354-low-estrogen#symptoms-and-causes