What Causes Menstrual Cycles to Change Dates?


Picture this. You’ve taken a few days off work for a little weekend getaway. Obviously, you’ve planned the whole thing around your period dates - you want to be as stress free as possible on your mini vacation. However, as luck would have it, boom! Your period shows up a week early, just as you’re set to leave.


If this sounds like a familiar story, you know the struggle. It’s probably happened to you or someone you know, and it can be quite common; even regular periods have the habit of switching around dates once in a while.


Period date shifts happen for a variety of reasons, and we’ll help you understand why. But before we dive into all of those, let’s take a look at what we consider “normal”. 


According to the Mayo clinic, cycles shorter than 21 days are irregular, as are ones that extend for over 38 days. That means, if the time between the first day of one period to the day before your next period is either under 21 days or over 38 days, something may be wrong and it is worth investigating with your healthcare provider. 


While minor changes in dates are normal and need not be reason to worry, it is helpful to track your period to know exactly what’s going on. Using the help of online period trackers, or simply keeping a record in a diary can help. If you notice extended irregularities, we recommend taking this to a healthcare provider. 


For now, let’s look at some of the causes of changing period dates: 


    • Menarche, or simply put, your youth.
      In the first few years after you first get your period, it isn’t uncommon for it to be super irregular. Some people even go months between periods in their early years. It’s important not to panic if this is the case for you, however, it’s best to talk to an elder family member or doctor if you’re concerned. 

    • Pregnancy or breast-feeding.
      Of course, a missed period is an early sign of pregnancy. Post pregnancy as well, breast-feeding can cause delays to the return of your period.  It’s important to remember that it is still possible to conceive during this time, even though your period might not have returned.

    • Sudden changes in your weight.
      Drastic weight gain, sudden weight loss, excessive exercise, and/or increased physical activity are all things that can lead to period irregularities. Eating disorders can impact this as well, so it’s important to pay close attention and care for these aspects of your health first.

    • Polycystic ovary syndrome (PCOS).
      This is a hormonal disorder that is estimated to affect between 6 to 10% of menstruators. It occurs when the ovaries produce higher amounts of male hormones (androgens) that affect egg production. If this is the case, there are treatments that can help with hormone regulation. Read more about PCOS here.

  • Medications
    It is possible that some medications may disrupt your period cycle. According to medicalnewstoday.com, hormone replacement therapy, blood thinners, epilepsy drugs, antidepressants, aspirin and ibuprofen are some of the drugs that may cause irregularities. We recommend that you speak to your healthcare provider about any changes if this is the case.

  • Uterine fibroids.
    Fibroids are muscular growths that form on the walls of the uterus. They can cause long, heavy periods, and are often characterized by pelvic, lower back and leg pain. Because this causes periods to be longer than normal, it can result in the changing of dates, or minor bleeding in between periods.

    Most of the time, uterine fibroids are managed with over-the-counter medications and iron supplements. Once again, we recommend you see a healthcare practitioner if you’re experiencing these symptoms.

  • Thyroid problems.
    Both underactive and hyperactive thyroids can affect the intensity of your period, also causing irregularities and date changes.

  • Stress
    There’s a ton of research that suggests that stress can cause interference with your period. This happens because stress affects the part of your brain that controls the hormones needed for your cycle. Relieving stress is a simple way to help with this and get your period back on track. 

While the above causes are some of the more common ones, there are several changing factors that can affect your period dates. Smoking, contracting an STI or infection, or even more severe ovarian complications can cause period irregularities. If you have irregular cycles in a row, it’s best to consult your healthcare provider. 

Of course, it never hurts to always be prepared. We recommend carrying your nixit in your bag - we even have a little pouch designed for just that purpose! 



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