No two menstrual cycles are the same. Even for a single individual, periods can change from month to month. Some variations are considered within a healthy range while other irregularities are considered abnormal. The purpose of determining if your period falls within the “abnormal” range is not to define your health. Rather, it is to help you (and your doctor) figure out if there might be something else (even temporarily) causing your menstrual cycle to be thrown off and what can be done to get it back on track. So keep this in mind as you learn more about irregular cycles.
“Normal” cycle length
The average length of a menstrual cycle ranges from 24 to 38 days. It exists as a cycle because of molecules called hormones. Hormones are basically little messengers in your body that are sent from one body part to another and tell that body part to do something. We know a lot about hormones, including that they work in a predictable loop-like manner. These patterns direct the menstrual cycle.
The major hormones running the menstrual cycle are estrogen, progesterone, LH and FSH. These all work together to contribute to different cycle phases. However, disrupting the signaling from just one hormone can result in a disruption in all hormones of the menstrual cycle...and cause your cycle to be thrown off.
“Normal” irregularity
The most common cause of cycle length irregularity is a change in hormone signaling. These changes can be caused by a variety of factors, including stress and illness. However, there are two periods of time that irregularity (and abnormal hormone signaling) are expected: puberty and perimenopause. This is because the hormone signaling itself is naturally abnormal during these times.
During puberty, the body is just getting the hormone signaling warmed up. It’s similar to when you start a car. Turning the car on sets off a cascade of signals that eventually lead to a fully-functioning vehicle, but it takes a few seconds. For the body, it can take two to three years for the signals to become completely operational.
A similar process happens in reverse during perimenopause. Hormone levels start to fall. This disrupts established hormone signaling and often makes cycles unpredictable.
Stress and hormones
Beyond puberty and perimenopause, there are many other causes of menstrual irregularity. Stress is one major factor that can impact hormone signaling. When you're stressed, your body secretes a hormone called cortisol. Cortisol is known to interfere with the release of menstrual hormones, causing a delay in ovulation or a missed period. This means if you experience stress related to work, school or relationships, your period may come later than usual.
Nutrition and hormones
Diet and nutrition also play an important role in cycle length. If you’re not eating enough or if your diet lacks key nutrients, your body might not be able to produce the hormones needed to maintain a regular cycle. On the other hand, gaining or carrying too much weight can lead to an imbalance in hormones, which might make your cycles longer or irregular. People suffering from eating disorders or extreme changes in weight usually experience missed or unpredictable periods due to the fact that their bodies are not in a state of balance.
Exercise and hormones
Exercise extremes are also known to influence cycle length. While regular exercise is healthy, exercising too much can disrupt your cycle. This is common in athletes or people who do intense workouts, as their bodies might not have enough energy to support normal hormonal functions. As a result, periods might come later than expected or stop altogether.
Structural conditions
Certain medical conditions can also impact cycle length. One such example is polycystic ovarian syndrome, or PCOS, which can interrupt menstrual hormone signaling. Another condition that may cause irregular cycles is thyroid disease, which can reduce the amount of menstrual hormones in the body. Both conditions can lead to cycles that are very short, very long, or missed altogether. If you find that your cycle is not the same number of days from month to month, it is best to check with your doctor.
Medications
Birth control methods such as pills, patches or IUDs might affect the length of the cycle for some individuals. Because most birth control forms are fake hormones themselves, the main way they work is by taking over your body’s hormone signaling to reduce your risk of pregnancy. The majority of hormonal birth control methods make your cycle more regular, though some forms lead to lighter periods or may even stop them (especially over time). Non-hormonal methods of birth control generally do not affect the length of the cycle. When you have questions about how your birth control method works, it is always okay to discuss with your doctor.
Major life events
Major life changes including pregnancy or surgery cause temporary disruption in your menstrual cycle. It is healthy and expected that your period will take a couple months after giving birth to return to regularity, particularly if you are breastfeeding. Also, prolonged illness or major surgeries (especially those affecting the reproductive system) will cause temporary, self-correcting disturbances in one's cycle.
When to see a medical provider
It is normal for cycles to vary in length from time to time, and such variations should not be a cause for alarm. However, when the cycle remains irregular or suddenly becomes much shorter than usual, it is best to consult with a doctor. The only way to know for sure if your cycle is irregular is by keeping track. Taking notes on a calendar or using one of the many period apps to mark the first day and last day of your flow every month is easy and effective. This information can also be helpful if you need to speak with a physician about irregular cycles.
Treatment
Some medications and supplements have been shown to promote irregularity and get your period back on track. If you struggle with unpredictable period patterns, daily supplements in our Bye Irregularity package have been shown to help restore regularity and promote menstrual health.
If cycle length variations are caused by underlying conditions, prescription or surgical treatments are typically available. Doctors often recommend birth control pills or other medications to regulate your cycle when other interventions do not help. Lifestyle changes, like eating a balanced diet, exercising moderately and managing stress can also restore regularity. For conditions like PCOS or thyroid disease, specific hormone treatments are needed to eliminate the root cause of irregular cycles.
Conclusion
Cycle length might vary for many reasons, which include changes in hormonal levels, stress, dietary reasons, medical conditions, and lifestyle factors. While some variation is normal, large or frequent changes might mean it's time to talk to a doctor. By understanding the causes of cycle length variations and taking steps to monitor your periods, you can stay informed about your reproductive health and get help when needed.