Top Causes of Irregular Periods

Top Causes of Irregular Periods

Irregular menstrual cycles/periods are a common occurrence for many women, especially for women with confirmed hormone imbalance such as PCOS, but the reality is that all women will experience irregular cycles from time to time. In most cases cycles return to normal on their own, but for women dealing with irregular cycles for a long time, it may be worth investigating some underlying causes.  The period itself is not really to blame. The timing of ovulation is what dictates when the next period will arrive. The timing of ovulation can change every month leading to irregular menstrual cycles and irregular periods. Here are the top causes of irregular periods:

  1. Polycystic Ovary Syndrome (PCOS): PCOS is a metabolic disorder that can cause irregular menstrual cycles. It is characterized mostly by high androgenic hormones like testosterone or DHEA. In 70% of cases PCOS is linked to insulin resistance.  This prevents the regular release of eggs from the ovary and can oftentimes lead to the formation of small cysts on the ovary (which are not real cysts but a collection of undeveloped follicles that fail to ovulate). This condition can cause a wide range of symptoms, including acne, weight gain, and excessive hair growth.
  2. Hypothalamic Amenorrhea: Hypothalamic amenorrhea is a condition where the hypothalamus, a part of the brain that controls the reproductive system, does not release the necessary hormones required for ovulation. Estrogen is low and ovulation does not occur. In the majority of cases periods are missing for many years until the return of the first menstrual cycle. After that point periods may become irregular or before becoming regular again. This condition can be caused by energy deficiency due to eating disorders, excessive exercise, stress, or low body weight.
  3. Post-partum and Breastfeeding: If a woman breastfeeds, prolactin levels are high. Prolactin suppresses the menstrual cycle and periods are missing for a period of time. Fertility can return at any time, even if a woman is exclusively breastfeeding so it is important to monitor fertility signs but for most women prolactin levels steadily drop reaching low enough levels to trigger the return of the menstrual cycle by 6-7 months. Because prolactin levels are still high, periods are usually irregular for a few months. Quitting breastfeeding also creates hormonal change as all hormones dip for 3 months before returning to more normal levels. This can cause temporary irregular cycles and other symptoms.  If a woman does not breastfeed, it can still take a few weeks for cycles to become regular, however ovulation usually resumes much earlier and menstrual cycles become regular more quickly unless there is an underling hormone imbalance.
  4. Coming off Hormonal Birth Control: Depending on the type of birth control used and the the particular health status of the woman, It may take some time for the body to return to its natural hormonal balance after discontinuing birth control. Even if regular cycles are resumed right away and pregnancy is possible it still takes at least 9-12 months for the ovary to resume normal function. Some birth controls can cause irregular or missing periods for up to 18 months. If periods are missing for a long portion of time, medical investigation may be required.
  5. Thyroid Problems: Thyroid imbalances, including hypothyroidism and hyperthyroidism, can disrupt menstrual cycles. In most cases, hypothyroidism causes long cycles and heavy bleeding.
  6. Luteal Phase Defect: The luteal phase is the second half of the menstrual cycle, which occurs after ovulation. A healthy luteal phase should be between 11-16 days long. If this phase is too short, it can lead to shorter menstrual cycles which are considered irregular and can cause difficulty conceiving.
  7. Peri-menopause: Peri-menopause is the period before menopause when hormonal changes can cause irregular periods. Hormones fluctuate wildly during perimenopause and can become irregular becoming too close together and further apart depending on hormone levels. Eventually periods become more and more spaced apart until the stop at the arrival of menopause.
  8. Stress: Stress can impact the hormonal balance and lead to irregular menstrual cycles. This is seen through delayed ovulation which causes a delay in period. On a menstrual chart it can be observed as a ‘stress patterned menstrual cycle” where there is attempted ovulation multiple times throughout the cycle before ovulation is confirmed. Stress can also interfere with the quality of ovulation and lower progesterone enough to shorten the luteal phase leading to luteal phase defect and shorter cycles.
  9. Time Zone Travel: Traveling through time zones can cause disruptions to the body’s circadian rhythms, including menstrual cycles.
  10. Temporary illness like a cold or flu: Illness can disrupt the body’s natural hormonal balance, leading to a delay or early onset of menstruation. Additionally, taking medications such as antibiotics or decongestants can affect hormonal levels and cause menstrual irregularities. While this is typically a temporary issue and cycles should return to normal once the illness subsides, it’s still important to monitor menstrual cycles to identify any changes or patterns that could indicate underlying health issues.


For individuals with irregular cycles, learning to chart can provide valuable clues about their health. Charting can help identify any patterns or trends in menstrual cycles, which can indicate potential health issues.


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