# When and Why Do Irregular Periods Happen?

- Page: https://www.carewithki.com/en/discover/when-and-why-irregular-periods-happen
- Published: 6 July 2026
- Topics: Hormonal balance, Periods
- Topic page: Menstrual Cycle and PMS https://www.carewithki.com/en/discover/topic/periods-and-pms
- Publisher: care with .ki (content principles: https://www.carewithki.com/en/editorial-policy)

![When and Why Do Irregular Periods Happen?](https://www.carewithki.com/blog/adet-duzensizligi-ne-zaman-ve-neden-olur.jpg)

> According to the standards of the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO), a healthy menstrual cycle is defined by these parameters:

## What Should a Normal Menstrual Cycle Be Like?

According to the standards of the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO), a healthy menstrual cycle is defined by these parameters:

- Cycle Length: The time from the first day of one period to the first day of the next should be between 24 and 38 days.
- Bleeding Duration: Bleeding that lasts 4 to 8 days is considered normal.
- Amount of Bleeding: An average blood loss of 30 to 80 ml per cycle (about 2–3 tablespoons, or 3–6 standard pad/tampon changes a day) is normal.
Anything outside these limits is clinically called "abnormal uterine bleeding" (AUB), or, in everyday language, irregular periods.

## When and Why Do Irregular Periods Happen?

Menstrual regularity is controlled by a complex hormonal chain called the hypothalamic-pituitary-ovarian (HPO) axis. The slightest deviation in this chain leads to irregularity. At certain stages of life and in some specific situations, these irregularities become more frequent:

### 1. Transitional Stages of Life (Physiological Causes)

- Puberty (After Menarche): In the first 1–3 years after the first period, because the HPO axis has not yet fully matured, anovulatory cycles (cycles without egg release) and irregularities are very common.
- [Perimenopause](https://www.carewithki.com/en/discover/what-is-perimenopause-what-changes-in-your-40s) (the Transition Before Menopause): As menopause approaches, the ovarian reserve decreases and oestrogen and progesterone fluctuate. Cycles may become shorter or longer, or periods may stop for months.

### 2. Endocrine and Metabolic Disorders

- Thyroid Dysfunction: Hypothyroidism (an underactive thyroid gland) causes heavy and long bleeding, while hyperthyroidism (an overactive one) causes late periods or very little bleeding. Thyroid hormones directly affect the synthesis of the proteins that bind sex hormones.
- Hyperprolactinaemia: A high level of prolactin, the milk hormone (due to stress, a pituitary adenoma or some medicines), suppresses egg release.
- Polycystic Metabolic Ovary Syndrome (PMOS): Formerly known as PCOS, it is the most common cause of hormonal/metabolic irregularity in women of reproductive age. It is now called PMOS because it has become clear that the condition is not limited to the ovaries but also involves insulin resistance and metabolic processes. High androgen (male hormone) levels prevent egg release, resulting in infrequent periods (oligomenorrhoea) or no periods at all (amenorrhoea).

### 3. Lifestyle and Environmental Factors

- Chronic Stress: An increase in the hormone cortisol can suppress the release of GnRH (gonadotropin-releasing hormone) in the hypothalamus, leading to a late period or periods stopping altogether.
- Sudden Weight Changes and a Low Body Mass Index: When body fat falls below a critical level (especially with eating disorders or intense athletic performance), oestrogen synthesis stops, causing "functional hypothalamic amenorrhoea".

### 4. Drug Interactions

- Irregular use or a new start of birth control pills, [emergency contraception](https://www.carewithki.com/en/discover/what-does-the-morning-after-pill-do) (morning-after pills), some antidepressants (SSRIs can raise prolactin), antipsychotics and corticosteroids can directly affect menstrual regularity.

## When Should You Worry?

Although not every late or irregular period is an emergency, if you have one or more of the following symptoms, you should see a specialist in obstetrics and gynaecology (a gynaecologist) without delay:

- A 90-Day Delay: If you have had no period at all for 3 months or longer without being pregnant (secondary amenorrhoea).
- Frequent Cycles: If the time between the start dates of your periods has started to be shorter than 21 days.
- Very Heavy Bleeding: If your bleeding is heavy enough to completely soak more than one pad/tampon an hour, if you wake up at night to change your pad or if you pass clots the size of a coin (menorrhagia, which brings a risk of anaemia).
- Bleeding That Lasts More Than 7 Days: If your menstrual bleeding regularly lasts longer than 7–8 days.
- Bleeding Between Periods: If you have spotting or noticeable bleeding between two normal periods (metrorrhagia).
- Severe Pain: If there is severe pelvic pain with your periods that paralyses daily life and doesn't respond to over-the-counter painkillers (it may be a sign of endometriosis or fibroids).
- Bleeding After Menopause: Any bleeding or spotting, whatever the amount, after entering menopause (after at least 1 year with no periods at all) (it must be examined because of the risk of endometrial cancer).

## What Can You Do?

Treating the underlying cause of irregularity is personal and should be carried out under a doctor's supervision. But to support your general menstrual health, you can take these steps:

- Track Your Cycle: With the help of digital apps or a calendar, note the day your bleeding starts, how long it lasts and how heavy it is. This data is your gynaecologist's most valuable diagnostic tool.
- Nutrition and Supplements: Under the supervision of your doctor and pharmacist, optimise your levels of myo-inositol, shown in clinical studies to support insulin resistance and the HPO axis, [magnesium](https://www.carewithki.com/en/discover/is-all-magnesium-the-same-which-magnesium-does-what) and vitamin B6, which play a role in hormonal balance, and vitamin D if you are deficient.
- Avoid Random Herbal Remedies: Some herbal teas or remedies taken on hearsay (for example, uncontrolled use of chasteberry or yarrow) can strain the liver enzymes or further complicate an existing hormonal imbalance. Always consult your pharmacist before taking supplements.

## References & Scientific Sources

- ACOG (American College of Obstetricians and Gynecologists). (2021). Screening and Management of Abnormal Uterine Bleeding in Adolescent Patients. Committee Opinion No. 651.
- Munro, M. G., et al. (FIGO Menstrual Disorders Committee). (2018). The FIGO FIGO Systems for Nomenclature and Classification of Causes of Acute and Chronic Abnormally Uterine Bleeding in the Reproductive Years. International Journal of Gynecology & Obstetrics, 143(3), 393-408.
- Bulsara, J., et al. (2021). A review of polycystic ovary syndrome: An diagnosis, pathogenesis, and management update. Journal of Clinical Endocrinology & Metabolism, 106(7).
- World Health Organization (WHO). (2019). International Classification of Diseases for Mortality and Morbidity Statistics (11th Revision). Menstrual cycle disorders.
- AE-PCOS Society & International Consensus Criteria (2025/2026): Redefining PCOS to PMOS: Shifting the Paradigm from Ovarian Cysts to Metabolic and Endocrine Dysfunction. Journal of Clinical Endocrinology.

_This article is general information; it is not a diagnosis or treatment recommendation._