What are irregular periods (oligomenorrhea)? What causes irregular periods?

What are irregular periods (oligomenorrhea)? What causes irregular periods?


MNT Knowledge CenterOligomenorrhea is a medical term which generally refers to irregular or infrequent menstrual periods with intervals of more than 35 days – however, the duration may vary.

A period, or menstruation, is the shedding of the endometrium – the lining of the uterus. Menstruation is also called menses. All female humans, as well as a number of other female mammals, have regular periods during their reproductive age. Menstruation, which includes bleeding from the vagina, occurs mainly among humans and similar animals, such as primates. In many mammals, the endometrium is reabsorbed.

As far as humans are concerned a period is a bleed from the womb (uterus) that is released through the vagina. Human females have a period about every 28 days – most women have between 11 and 13 menstrual periods each year. However, some women may have a 24-day cycle while other may have a 35-day one. A period is part of the female’s menstrual cycle.

Periods usually start between the ages of 10 and 16 (during puberty), and continue until the menopause, when woman is 45 to 55 years old. Periods can take up to two years to occur in a regular cycle. After puberty, the majority of females have a regular menstrual cycle (the length of time between each period is similar).

Menstrual bleeding usually lasts for about five days, but can vary from two to seven days.

Some women have irregular periods – the time between periods, as well as the amount of blood shed varies considerably. This may have several possible causes, including a change in contraception method, a hormone imbalance, hormonal changes in perimenopause, and endurance exercises.

Treatments for irregular periods during puberty and around the menopause are not usually necessary, as they are quite common.

A large European study found that hay fever and asthma were linked to a higher risk of irregular periods.

Women with delayed sleep phase syndrome are more likely to report irregular menstrual cycles and premenstrual symptoms, according to scientists at Northwestern University in Chicago, USA.

What are the causes of irregular periods?

There are two main reasons for irregular periods:

  • A change in the contraception method
  • An estrogen and/or progesterone imbalance (hormones which regulate the menstrual cycle)

Examples include:

  • Polycystic ovarian syndrome (polycystic ovary system) – also known as PCOS, or the Stein-Leventhal Syndrome. Many cysts (small, fluid filled sacs) develop in the ovaries. It is a condition characterized by irregular or no periods, obesity, acne, and excess hair growth.

    Women with PCOS have a disorder of chronically abnormal ovarian function and abnormally high levels of androgen (hyperandrogenism). Androgen is a male sex hormone – the major androgen is testosterone.

    According to the CDC (Centers for Disease Control and Prevention), USA, approximately 5% to 10% of women of reproductive age are affected by PCOS.

    A woman with PCOS does not release an egg every month (she does not ovulate). Patients with PCOS have a considerably higher risk of hypertension (high blood pressure), diabetes, heart disease and endometrial cancer (cancer of the uterus). Experts say that in many cases weight loss and exercise can eliminate much of the risk.

  • A woman’s imbalance of hormones, which may lead to irregular periods, may also be caused by:
    • Extreme weight loss. Low body weight is a common cause of irregular or missed periods.
    • Extreme weight gain. Obesity may sometimes cause menstrual problems.
    • Emotional stress
    • Eating disorders, such as anorexia or bulimia can lead to hormone imbalances, resulting in irregular or missed periods.
    • Endurance exercises – endurance athletes, such as those that compete in marathons, may have irregular or missed periods.


  • Age
    • Puberty – irregular periods for a few years after puberty are common, and not considered unusual. It may take a few years for the hormones that control menstruation – estrogen and progesterone – to reach a balance.
    • Before the menopause – as the menopause approaches women commonly have irregular periods. The amount of blood shed may also vary. Menopause occurs when it has been 12 months since the woman has had a menstrual period.


  • Breast feeding – most women do not start having periods again until they stop breastfeeding.
  • Thyroid disorder – irregular periods may be caused by a thyroid disorder. The thyroid gland produces hormones that affect our bodies’ metabolism.
  • Contraceptives – an IUD (intrauterine device) may cause heavy bleeding, while the contraceptive pill can cause spotting between periods. Initially, when using the contraceptive pill for the first time, it is not uncommon for the woman to experience breakthrough bleeds (small bleeds). Breakthrough bleeds are generally shorter and lighter than normal periods – they usually go away after a few months.
  • Cancer – bleeding between periods may be caused by cervical cancer or uterine cancer (cancer of the uterus/womb). These cancers may also cause the woman to bleed during sex. Bleeding caused by these cancers is rare.
  • Emdometriosis – this is a condition in which cells that are normally found inside the uterus (endometrial cells) are found growing outside it. That is, the lining of the inside of the uterus is found outside of it. Endometrial cells are the cells that shed every month during menstruation, and so endometriosis is most likely to affect women during their childbearing years. The cellular growth is not cancerous, but benign. Though there are not always symptoms, it can be painful and lead to other problems.

    Problems may occur if released blood gets stuck in surrounding tissue and damage it, causing severe pain, irregular periods and infertility.

  • Pelvic inflammatory disease – an infection of the female reproductive system. It is the most common and serious complication of sexually transmitted diseases, apart from AIDS, among women. If detected early it can be treated with antibiotics. However, if it spreads and damages the fallopian tubes and uterus it can result in chronic episodes of pain (in medicine “chronic” means long-term, for life). Of the many symptoms are included bleeding between periods and after sex.

What are the treatment options for irregular periods?

If the irregular periods occur during puberty or as the woman approaches the menopause, treatment is not usually necessary.

  • Contraception – any patient who has been fitted with an IUD (intrauterine device) and has been having irregular bleeding that does not go away after a few months should talk to a health care professional and discuss alternative contraception options.

    Women who are on a new contraceptive pill that is causing irregular bleeding for more than a couple of months will probably be advised to switch to another pill.

  • PCOS (polycystic ovarian syndrome) – if the woman is overweight/obese and has PCOS, as well as irregular periods, losing weight may help resolve the irregular periods. On losing weight the body does not need to produce so much insulin, resulting in lower testosterone levels and a better chance of ovulating.

    If the woman is not trying to become pregnant, the doctor may prescribe low-dose birth control pills that contain a combination of estrogen and progesterone (synthetic). They lower androgen (male hormone) production and give the body a rest from the effect of non-stop estrogen, lowering the risk of endometrial cancer, as well as correcting abnormal bleeding.

    Alternatively, the woman may take progesterone for about 10 to 14 days each month – this is likely to regulate the periods, as well as offering protection against endometrial cancer (does not improve androgen levels).

    The doctor may prescribe metformin (Glucophage, Glucophage XR) – this is an insulin-lowering oral drug for type 2 diabetes, resulting in more probable ovulation and regular periods. The medication also slows down the progression of type 2 diabetes if the patient already has pre-diabetes and subsequently loses weight.

  • Thyroid problems – treatment may involve:
    • Prescribing medication that slows down the production of thyroid hormones.
    • Radioactive iodine therapy – radioiodine treatment is a kind of radiotherapy that targets tissue in the thyroid gland, resulting in a reduction in the amount of thyroid hormone the thyroid gland produces.
    • Partial thyroidectomy – part of the thyroid gland is surgically removed.


  • Psychological therapy – if emotional stress or sudden weight loss are diagnosed as a cause of irregular periods, the doctor may advise counseling or stress management. This may include relaxation techniques, stress management, and talking to a therapist.

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