Period Changes During Perimenopause: What’s Normal, What’s Not

If you’re noticing menstrual cycle changes in your 40s, perimenopause may be the reason. Period changes are often one of the first signs of perimenopause, and for many women, periods don’t simply stop overnight. Instead, cycles become unpredictable — heavier, lighter, closer together, farther apart, or completely erratic – long before periods stop completely.

If you’ve been told that your changing periods are “part of menopause” but still feel unsure about what’s normal, you’re not alone. Understanding why these changes happen—including a pattern known as LOOP cycles—can help you better advocate for your health and recognize when further evaluation may be needed.

Understanding Period Changes in Perimenopause

Menopause is officially diagnosed after 12 consecutive months without a period, but the hormonal shifts that drive cycle changes can begin years before that point. While the average age of menopause in Canada is 51 (Menopause Foundation of Canada, 2025), most women begin noticing menstrual changes during perimenopause, the transitional phase leading up to menopause. These cycle changes typically start in the mid-40s, and can last 8-10 years before the final menstrual period, although timing varies from person to person.

What a Typical Menstrual Cycle Looks Like

Before perimenopause, menstrual cycles tend to follow a predictable pattern, often averaging around 28 days:

• Follicular phase: The brain releases follicle-stimulating hormone (FSH), signaling the ovaries to mature an egg. Estrogen is the dominant hormone during this phase and builds the uterine lining.
• Ovulation: Around the middle of the cycle, a surge of luteinizing hormone (LH) triggers ovulation, and the body releases an egg.
• Luteal phase: Progesterone becomes the dominant hormone, stabilizing the uterine lining in case of pregnancy.
• Menstruation: If pregnancy doesn’t occur, estrogen and progesterone fall, the uterine lining sheds, and a period begins, usually lasting 5-7 days.

This coordinated rise and fall of hormones is what creates a regular, predictable cycle.

Why Cycles Become Irregular in Perimenopause

As perimenopause begins, the communication between the brain and ovaries becomes less consistent. The brain releases higher and more variable levels of FSH in an attempt to stimulate the ovaries, but the ovarian response becomes unpredictable.

As a result:

• Ovulation may occur earlier, later, or not at all
• Progesterone production becomes less reliable
• Estrogen levels fluctuate widely—sometimes higher than in earlier reproductive years, sometimes much lower

These hormonal shifts can lead to:

• Shorter or longer cycles
• Skipped periods followed by heavy bleeding
• Heavier or lighter flow
• Symptoms that change from month to month

One important pattern that helps explain this unpredictability is the LOOP cycle.

What is a LOOP Cycle?

A LOOP cycle (luteal out-of-phase cycle) is a pattern of menstrual disruption that can occur during perimenopause. It helps explain why bleeding patterns may feel confusing or erratic.

During perimenopause, the ovaries become less responsive to FSH, and estrogen production becomes irregular. Because estrogen feedback to the brain is inconsistent, the pituitary gland may release persistently elevated FSH.

In a LOOP cycle:

• FSH levels remain high enough to start developing a second egg even while the first cycle is still in its luteal phase (after ovulation)
• This can lead to a second rise in estrogen layered on top of the existing cycle
• Progesterone levels may decline earlier or be insufficient

The effect on the next menstrual cycle depends on whether this second egg is released (ovulation):

• If ovulation occurs, the next cycle may be unusually short (sometimes under 21 days)
• If ovulation does not occur, estrogen eventually drops and the cycle maybe longer than usual (often longer than 36 days)

LOOP cycles are common during early perimenopause, occurring in about one in four cycles (North American Menopause Society, 2019). They help explain irregular bleeding patterns, skipped periods, and unexpectedly short or long cycles. While these changes are often normal, understanding bleeding patterns remains important.

What Changes Should I Be Concerned About? 

Perimenopause is a time of hormonal transition, and changes in menstrual bleeding are common. For many women, this unpredictability is frustrating—but normal.

That said, not all bleeding changes should be ignored. Knowing what’s expected versus what deserves medical attention can bring peace of mind and help catch problems early.

Bleeding changes that are often normal in perimenopause

These patterns are usually related to hormonal fluctuations and may come and go:

• Periods that arrive earlier or later than usual
• Occasional heavier or lighter flow
• Spotting around ovulation
• Skipping a period, followed by a heavier one the next month
  

While inconvenient, these changes alone are often part of the transition.

When menstrual bleeding should be checked

It’s important to speak with a healthcare provider if bleeding becomes heavy, persistent, or unusual:

Heavy bleeding

• Soaking through a pad or tampon every 1-2 hours
• Passing large clots (bigger than a toonie) frequently
• Periods lasting longer than 7–10 days
• Needing overnight changes, or multiple forms of period products at once (eg. tampon with pad or brief)

Bleeding outside your normal cycle

• Spotting or bleeding between periods
• Bleeding after sex

Bleeding after long gaps

• Any bleeding after menopause (defined as 12 months without a period)

Bleeding with other symptoms

• Fatigue, dizziness, or shortness of breath 
• Pelvic pain, pressure, or persistent bloating
• Unexplained weight loss or fevers

Sudden or disruptive changes

• A rapid shift from manageable periods to very heavy or frequent bleeding
• Bleeding that interferes with daily activities, sleep, or quality of life
  

Why Evaluation Matters

Most bleeding changes during perimenopause are caused by hormonal changes, but sometimes there are other treatable reasons, such as:

• Fibroids or uterine polyps
• Thyroid disorders
• Thickening of the uterine lining
• Gynecological cancers

Getting evaluated by a health care professional doesn’t mean something is wrong—it often means reassurance and, when needed, access to effective treatment options.

The Bottom Line

Perimenopause is a natural transition–but your symptoms still deserve attention. If bleeding feels excessive, persistent, or simply “not right,” that alone is a valid reason to seek care.

Trust your body, ask questions, and remember: you don’t have to just “push through” uncomfortable or disruptive symptoms during this phase of life.