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Menstrual Cycle Irregularity: Perimenopause or Something Else?

A woman tracking her cycle

Your menstrual cycle is acting a bit dodgy. Maybe it’s longer, shorter, lighter, or heavier. How can you tell if it’s perimenopause or if something else is going on? Menstrual cycle irregularity is one of the major clues that you’re in perimenopause. Changes in your cycle usually begin in your 40’s but can happen as early as your 30’s.

A Typical Menstrual Cycle

Although it varies between individuals, the average length of a menstrual cycle (the time between menstrual periods) is 28 days.

The menses phase of the menstrual cycle is when you have your period—bleeding as you shed the lining of your uterus. This usually lasts 3-7 days.

Next comes the follicular phase. During this time, your ovaries begin maturing eggs. Estrogen and follicle-stimulating hormone (FSH) levels increase, and the lining of your uterus (endometrium) begins to thicken.

Ovulation takes place about halfway through the menstrual cycle. Luteinizing hormone (LH) increases, causing a mature egg to release.

The last phase of the cycle is the luteal phase. This is when the egg makes its way down your fallopian tube. Rising progesterone levels finish preparations to the endometrium. You’re now ready to get pregnant if a sperm finds its way. If not, estrogen and progesterone levels drop and cause you to move back into the menses phase.

Menstrual Cycle Irregularity During Perimenopause

Perimenopause is the transitional time between fertility and menopause, the latter life stage when you no longer have a period and can’t get pregnant. Although it can occur earlier or later, most women will begin perimenopause in their 40s. The average age of onset is 40-44 years old.

When your ovaries begin the process of shutting down their egg-maturing capabilities, your hormones go through major changes. FSH levels will elevate in an attempt to mature eggs, but estrogen and progesterone levels begin to drop.  These hormone changes lead to cycle irregularities. You might skip a period or have two periods in quick succession. Your flow might be heavier or lighter than you are used to.

During perimenopause, you might not ovulate every month, even if you get a period. However, it’s always possible that you are ovulating even if your periods are irregular. You may still get pregnant, so don’t discontinue your birth control until you’ve reached menopause.

In the beginning stages of perimenopause, you might only notice subtle changes to your menstrual cycle. As perimenopause progresses, you’ll experience greater variability in the timing and characteristics of your periods. This is an indication that you are getting closer to reaching menopause.

Once you have not had a period for 12 consecutive months not due to another cause, you have reached menopause. Only now can you be certain that you are no longer ovulating. 

Other Causes of Menstrual Cycle Irregularity

Although perimenopause is the most common cause of menstrual irregularity in midlife, it’s always a good idea to check in with your primary care provider to rule out other issues.

Your provider may test your hormone levels to ascertain if you are, indeed, in perimenopause. If FSH is high and estrogen and progesterone are low, you can be sure you’re in perimenopause. If not, there are other causes of irregular and unusual menstruation.

While this list is not exhaustive, it illustrates why it’s important to verify the cause of your cycle changes.


While unexpected after a certain age, it is always a possibility if you are still menstruating.

Uterine Fibroids

Fibroids are growths in the uterus that can cause excessive bleeding during menstruation.

Thyroid Disorders

Both too little (hypo-) or too much (hyper-) thyroid hormone can cause changes in your menstrual cycle.

Polycystic Ovary Syndrome

PCOS is a common endocrine disorder that can lead to irregular periods.

Extreme Weight Loss

Major weight loss, low body weight and low body fat can cause anovulation (loss of menses). This can occur when someone has an eating disorder or is competing at a high level of athletics with inadequate rest and nutrition. It usually reverses with weight gain and improved nutrition.


Women with diabetes are more likely to have irregular periods.


Some medications are known to cause changes in menstruation.

Cervical and Uterine Cancers

Cancers of the reproductive organs can cause vaginal bleeding between periods or heavier than normal menstruation.

Tracking Perimenopause

Tracking your monthly cycles can be a big help when you begin to notice they’re changing. Whether you keep records on paper or one of the many available apps, it helps to pay attention to your menstrual patterns.

The Midday app has a science-backed menopause progression tool that can help you determine where you are in your reproductive journey (from premenopause to early or late perimenopause to approaching menopause to postmenopause). This information can help you understand what you’re experiencing and prepare for what comes next.

Each month, Midday will check in with you and evaluate your progression. In some cases, Midday can't evaluate your menopause progression. For example, if you're using a type of contraception that suppresses your period. In that case, it's best to consult your healthcare provider to discuss where you are in your journey.

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