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Understanding Irregular Periods

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Irregular periods can be the norm for girls and perimenopausal women — those at the beginning or those transitioning to the end of their menstrual stage of life — but for everyone else, an irregular period might be a sign that something is amiss.


A woman’s monthly cycle, or menses, is the way the body prepares for pregnancy. The blood that flows from a woman’s body each month is made up of blood and tissue that originates in the womb (uterus). This mixture is shed each month, flowing out of the uterus, through the cervix and out of the vagina.

A woman’s menstrual cycle, or period, begins on the first day the blood flows out of her body. Though menstrual cycles can range in length, the average is 28 days, which means it is 28 days from the first day of one cycle until the first day of the next cycle.

A woman’s hormones, which are chemicals found in the body, trigger the monthly menstrual cycle. In various phases, the lining of the uterus (endometrium) grows and thickens, an egg (ovum) forms and is released (ovulation) and travels through the fallopian tubes to the uterus, where it attaches to the uterine wall, or lining. If fertilized by sperm, the woman becomes pregnant. If not fertilized, the thickened lining is shed through menstruation, with bleeding that lasts three to five days, on average.

Most girls start having their period at about age 12. Some girls start young — at 8 — while others may start late — at 16. When a woman reaches menopause, at an average age of 51 in the United States, her periods stop.

Besides the bleeding, a normal menstrual period may include such symptoms as:

  • A facial acne breakout
  • Feeling sad or weepy or irritable
  • Trouble sleeping
  • Pain in the lower back or pelvic area
  • Swollen or painful breasts
  • Feeling bloated
  • Craving certain foods or drinks

What is an irregular period?

Your period is considered irregular if your monthly cycle either comes too frequently, not frequently enough or is inconsistent from month to month. For example, the number of days from the first day of your last period to the first day of your next period shouldn’t be shorter than 24 or longer than 38. Another way your period can be irregular is if it varies by more than 20 days a month — for instance, if your period goes from a 28-day cycle to a 49-day cycle and then back to a 28-day cycle.

If your period is irregular, check with your doctor to make sure something serious is not responsible.

Causes of irregular periods include:

  1. Thyroid problems. Your thyroid gland makes hormones that influence your period. If you have hyperthyroidism, that means your body has an overactive thyroid and is making too much thyroid hormone. This can lead to lighter and fewer periods. On the other hand, if you have hypothyroidism — when your body doesn’t make enough of this hormone — you can have heavier menstrual bleeding. Thyroid disease can have an even greater impact, causing amenorrhea, which is when your period stops altogether for months or even longer.
  2. Medications. Certain medications can affect your period. These include anxiety and epilepsy drugs, hormone replacement therapy, many nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, aspirin and other blood thinners, chemotherapy drugs and even medication to correct a thyroid problem.
  3. Excessive prolactin. Prolactin is a hormone that helps control the menstrual cycle. It also helps breasts grow in puberty and is responsible for making breast milk after pregnancy. However, too much prolactin — called hyperprolactinemia — can cause irregular periods.
  4. Pelvic inflammatory disease. Most often caused by a sexually transmitted disease, pelvic inflammatory disease is an infection in the reproductive organs. Irregular periods can be a sign of this condition.
  5. Stress. It’s not uncommon for stress to affect every area of your health, and that includes your monthly menstrual cycle. Studies have linked prolonged stress to irregular periods, according to the U.S. Office on Women's Health.
  6. Diabetes. Many people who have diabetes aren’t aware that they have it. Or those who know they have it don’t always manage it properly. Either way, irregular periods can be a byproduct of type 1 and type 2 diabetes when the disease is not properly managed through diet, exercise and, in some cases, medications.
  7. Eating disorders and obesity. Anorexia (self-starvation), bulimia (eating large amounts of food and then throwing up or taking laxatives) and binge eating disorders can result in missed or irregular periods. Likewise, if you’re obese, your body makes more of the hormone estrogen, which can change your menstrual cycle, resulting in irregular periods.
  8. Polycystic ovary syndrome (PCOS). This condition can cause ovarian cysts, a hormonal imbalance and irregular periods. About 1 in 10 women who have irregular periods have PCOS.
  9. Hormone-based birth control. Birth control methods that rely on hormones to prevent ovulation — both pills and devices like the IUD — can change the flow of your periods. It may take a few months for periods to get into a regular pattern when you start and when you stop using them. Also, some women who take birth control pills made only of the hormone progestin, rather than a combination formula, may get some bleeding between periods.
  10. Exercise-induced amenorrhea. Intense exercise coupled with too little food can put your body in starvation mode, meaning it shuts down functions it doesn’t consider essential, like reproduction. This could mean irregular or missed periods and a dangerous stop in estrogen production.
  11. Uterine polyps and fibroids. Both types of growths can develop in the lining of the uterus. While fibroids can start small, they can eventually grow to the size of a grapefruit, and it’s possible to have more than one. Even though neither polyps nor fibroids are cancerous, they can increase the amount of blood flow during periods (and increase discomfort) or in between periods.
  12. Endometriosis. This is when the tissue that normally lines the uterus and leaves the body during menstruation starts growing outside of the uterus. It can’t be expelled, but it can cause abnormal bleeding both before and during menstruation.
  13. Cervical or uterine cancer. Unusual bleeding or spotting, especially between periods or after menopause, is a common sign of uterine cancer. The most common type of uterine cancer is endometrial cancer, which starts in the lining of the uterus. Abnormal bleeding is also a sign of a pre-cancerous condition called endometrial intraepithelial neoplasia. Changes like irregular or heavier bleeding than what's normal for you can also be caused by cervical cancer.
  14. Perimenopause. While menopause marks the end of a year without any periods, perimenopause is the transition phase that can precede it for years. Because your hormone levels are changing, your usual pattern of ovulation followed by menstruation is changing, too. You might experience all kinds of variations — irregular bleeding or spotting, heavier and longer periods or lighter and shorter ones, fewer or more days between periods and missed periods.
  15. Pregnancy and breastfeeding. It’s possible to have some bleeding when you’re pregnant. It can happen as the newly fertilized egg implants itself in the uterus. But it can also indicate a problem, so always call your doctor any time you notice any bleeding. Breastfeeding after your baby is born can cause a delay in the return of your period, and for some women, this can last as long as the breastfeeding.

When to see a doctor for irregular periods

Every woman should have an annual exam with a gynecologist to make sure everything is alright. Additionally, contact your doctor if:

  • Your periods are painful and accompanied by severe cramping
  • You bleed or spot between periods
  • Your periods have been light or moderate, but suddenly became heavy
  • You haven’t had a period for 90 days
  • There are fewer than 21 days between your periods
  • There are 35 days or more between your periods
  • Your periods last longer than a week

Diagnosing the cause of irregular periods

Getting an accurate diagnosis starts with you. Keep track of your monthly cycle so you can bring the information to your doctor’s appointment. Be sure to note how long your period lasts, how many days there are between your cycles, if your flow is heavy (how many tampons or pads you use in a day), whether you pass large blood clots, if you bleed or spot between periods and if you have menstrual pain.

Your doctor will most likely do a thorough pelvic and physical exam and may also do a pap test. Other tests may include:

  • Blood tests to rule out anemia and other conditions
  • Vaginal culture to rule out infections in the reproductive area
  • Pelvic ultrasound to check for cysts or fibroids
  • Biopsy, which involves removing a sample of tissue and having it tested for such things as cancer, an hormonal imbalance or endometriosis

Treatment options vary depending on the cause

If you have irregular periods, any treatment would depend on your diagnosis — what's causing the irregularity. Factors you and your doctor will consider should also include your symptoms and your stage in life (for instance, if you're trying to get pregnant).

Common treatments include:

  • Birth control pills: Even though starting the pill causes some women to experience changes in their period, for others it can help regulate them. Of course, you wouldn’t take them if you’re trying to get pregnant, but for women who are not actively looking to start a family, this could be a good solution.
  • Counseling: If your irregular periods are caused by an eating disorder, obesity, diabetes or other issues related to food, your doctor may advise you to see a nutritionist or a counselor to help put together a healthy eating program.
  • Surgery: A surgical procedure may be needed to remove polyps or fibroids. Options include uterine artery embolization, which blocks blood flow to the uterus, or an endometrial ablation, which removes the blood vessels in the endometrial lining of the uterus. A hysterectomy is major surgery in which the uterus is removed.

Bottom line

While everyone’s menstrual cycle is unique, it’s important to know the signs of an irregular period. If your period cycle is too long or too short, if your flow is too heavy, if you’re bleeding between periods — these are signs that something might be amiss. Make an appointment with your doctor if you’re experiencing irregular periods to see if further tests, such as blood tests or a pelvic ultrasound, are needed. But remember, too, that it’s common for girls who have just started to menstruate and women who are beginning to go through perimenopause to have irregular periods.

Article references

  1. Office on Women's Health in the Office of the Assistant Secretary for Health at the U.S. Department of Health and Human Services, Period problems
  2. Penn Medicine, When Should You See a Doctor for Irregular Periods?
  3. Cleveland Clinic, Abnormal Menstruation (Periods): Diagnosis and Tests
  4. The Nemours Foundation, Irregular Periods
  5. U.S. Department of Health and Human Services, National Institutes of Health, What are the common treatments for menstrual irregularities
  6. Cleveland Clinic, Normal Menstruation
  7. Cleveland Clinic, What is abnormal menstruation?
  8. National Institute of Child Health & Human Development, Who is at risk of amenorrhea?
  9. University of Michigan, Medicines That Can Cause Changes in Menstrual Bleeding
  10., Thyroid disease
  11. USC Fertility: 5 Things You Should Know About Exercise-Induced Amenorrhea
  12. American College of Obstetricians and Gynecologists, Endometrial Cancer 
  13. Moffett Cancer Center, Uterine Cancer Symptoms
  14. American Cancer Society, Signs and Symptoms of Ovarian Cancer
  15. American College of Obstetricians and Gynecologists, Perimenopausal Bleeding and Bleeding After Menopause
  16. American College of Obstetricians and Gynecologists, Bleeding During Pregnancy 
  17. La Leche League, Menstruation