What is an irregular period, and why does it happen?

last updated: Aug 26, 2021

5 min read

Everyone has a unique experience with their periods. The average menstrual cycle length is around 28 days. While many women have a cycle that works like clockwork on a 28-day calendar, other women have much shorter or longer cycle lengths that may not be so predictable. 

So what causes an irregular period, and when does it require treatment?

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What is an irregular period?

Your menstrual cycle could be considered irregular if:

  • The number of days you spend on your period changes often.

  • The time between menstruation changes.

  • The heaviness of your flow changes in different months. 

  • You don’t get your period at all (or very infrequently)—this is called amenorrhea.

Causes of an irregular period

Here are some of the possible causes of irregular periods:

Perimenopause and menopause

Perimenopause is the natural decline in estrogen levels that eventually leads to menopause. Menopause is reached after one year without a menstrual period. This transition typically begins in the 40s and lasts around four years for most women (Peacock, 2021). 

Ovulation and menstrual irregularities are some of the early signs of perimenopause. Other symptoms of menopause include hot flashes, fatigue, vaginal dryness, trouble sleeping, and mood swings

Intrauterine device (IUD)

IUDs are a form of birth control where a device is inserted into the uterus. A common side effect of hormonal IUDs is less frequent and lighter periods.

Changing birth control pills

Oral contraceptives or hormonal birth control pills prevent pregnancy or help regulate hormonal imbalances. A common side effect when adjusting to a new hormonal birth control is changes to your regular menstrual cycle. 

Too much exercise

Overexercising, meaning too much intense exercise, may suppress reproductive hormones, leading to the loss of one’s period or irregular periods (Huhmann, 2020). 

Not enough food 

Adequate calories, vitamins, and minerals are important to maintain a healthy menstrual cycle. Nutrition deficiencies and anorexia may lead to irregular periods (Huhmann, 2020).

Polycystic ovary syndrome (PCOS)

Research suggests around 87% of women with irregular periods have PCOS (Dovom, 2016). PCOS is a condition that affects women’s hormonal health, leading to irregular menstrual cycles, elevated androgen hormones, and ovarian cysts. 

Other symptoms include irregular ovulation, weight gain, excess body hair, acne, and infertility.

Pregnancy or breastfeeding

Pregnancy is a common cause of missed periods. While you may experience occasional spotting while pregnant, you won’t experience a full period while pregnant. Breastfeeding after childbirth may delay the return of your regular menstrual cycle (Egbuonu, 2005). 


High stress levels impact health in a variety of ways, including hormone levels. Research suggests there is a relationship between higher stress levels and irregular periods (Kwak, 2019).

Thyroid problems

Thyroid dysfunction impacts hormonal health, and research shows it causes changes in menstrual cycles. Both hypothyroidism and hyperthyroidism may cause irregular periods (Ajmani, 2015).

Other symptoms of thyroid problems may include joint pain, obesity, irregular heartbeat, and infertility.

Uterine polyps

Uterine polyps, also called endometrial polyps, are noncancerous growths that develop on the lining of the uterus (womb). Polyps are made of the same tissue as your uterus. A common symptom of uterine polyps is irregular bleeding (Nijkang, 2019). 

Uterine fibroids

Uterine fibroids are noncancerous growths in the uterus made of connective fibrous tissue. One of the common symptoms of uterine fibroids is irregular and heavy uterine bleedings (De La Cruz, 2017). 

Other symptoms may include bloating, pelvic pain, and cramping.


Endometriosis is a medical condition where the tissue normally found in the uterus grows outside of the uterus. Symptoms can include heavy bleeding and shorter period durations (Tsamantioti, 2021).

Other symptoms may include pelvic pain, pain during sex, constipation, nausea, cramping, and infertility. 

Pelvic inflammatory disease

Pelvic inflammatory disease (PID) is an infection in the female reproductive system (uterus, ovaries, and fallopian tube). Bleeding between periods and abnormal vaginal bleeding are common symptoms of PID (Jennings, 2021).

Other symptoms may include pelvic pain and fever.

Asherman’s syndrome

Asherman’s syndrome is a rare condition where scar tissue reduces the size of the uterus or cervix. People with Asherman’s syndrome may experience less frequent periods or their period may stop completely (Smikle, 2021).

Uterine cancer

Uterine cancer, also called endometrial cancer, begins in the cells in the uterus. Symptoms include vaginal bleeding after menopause and bleeding between periods (Faizan, 2021). In rare cases, uterine cancer may be the cause of irregular bleeding.

Other symptoms may include pelvic pain, pain during sex, and unintentional weight loss.

Signs and symptoms of an irregular period

The signs of an irregular period include:

  • Bleeding between periods

  • Changes in cycle length

  • Longer than 35 days between periods

  • Changes time spent on your periods

  • Heavier or lighter period than usual

  • Absence of your period

The other symptoms you experience will vary based on the cause of your irregular periods. 

Risk factors for irregular periods

Depending on the cause of irregular periods, the risk factors will vary. Here are some common risk factors for irregular periods (Bae, 2018):

  • Family history

  • Medications, like hormonal contraceptives

  • Smoking

  • Stress levels

  • History of eating disorders

Diagnosing the cause of irregular periods

Typically a gynecologist, a physician who specializes in gynecology and female reproductive health, will diagnose the cause of irregular periods. Your healthcare provider will likely start by asking questions about your symptoms and medical history, such as:

  • How long do you usually have between periods?

  • Is your flow light or heavy?

  • Have you noticed any changes in your periods? If so, what changes?

  • Do you have a family history of any medical conditions?

  • Do you have any pelvic pain or other symptoms?

After reviewing your medical history and asking questions about your symptoms, your healthcare provider may complete some tests and exams, such as:

  • Pelvic exam: Often, a pelvic exam will be a routine part of assessing the cause for irregular periods. The physical exam will help them look for any abnormalities.

  • Blood tests: These may be ordered to assess hormone levels and signs of health conditions.

  • Ultrasound: An ultrasound is a primary tool used to diagnose many uterine conditions because it allows your healthcare provider to see the uterine tissue visually.

  • Biopsy: A biopsy is a tissue sample that can be used to diagnose some conditions, like endometriosis or cancer.  

  • Pap smear: A pap smear assesses any abnormalities in cells that could indicate precancerous or cancerous cervical cells. 

Treating irregular periods

Once your healthcare provider diagnoses the cause of your irregular periods, they will help you develop a treatment plan. Some of the recommendations and treatment options for irregular periods could include:

  • If you recently changed hormonal birth control, allow a few months for your body to adjust to the change.

  • If perimenopause or menopause is the cause of period changes, it’s a natural process. Other menopausal symptoms like hot flashes or vaginal dryness can be managed through medications or lifestyle changes.

  • Hormonal birth control may help to balance hormonal problems caused by conditions like PCOS, improving regularity. 

  • Weight loss may help improve PCOS symptoms.

  • Other lifestyle changes may help promote more regular periods, such as stress management, focusing on moderate-intensity workouts, and making sure to get adequate nutrition.

When to see a healthcare provider

Many different conditions could cause irregular periods. Some are more mild health conditions, while others may be more serious. If you’re experiencing irregular menstrual bleeding, it’s best to talk with your healthcare provider so they can assess your symptoms. 

Contact your healthcare provider if your notice changes in your periods or any of the following symptoms:

  • Three or more missed periods each year

  • Heavier than normal bleeding or large clots

  • Extreme pain or cramping during your period

  • Bleeding for longer than seven days

  • Bleeding between periods


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

August 26, 2021

Written by

Ashley Braun, RD, MPH

Fact checked by

Chimene Richa, MD