Women should know that their menstrual cycle is not like clockwork; there are some women who get their menstrual periods at regular basis, right on schedule every 28 days but also there are some women who have irregular menstruation. Their periods may be late or early and also they can vary in how heavy they are each time or how long they last. The normal menstrual cycle can be disrobed if the woman has an imbalance of the reproductive hormones oestrogen and progesterone or if she has changed her method of contraception. There are many factors which can cause a hormone imbalance from PCOS (polycystic ovary syndrome) to extreme weight loss and excessive exercise . On average, a woman’s menstrual cycle is lasting 28 days but these cycles can also vary from 24 – 35 days. After puberty, most women are developing a regular menstrual cycle which has around the same length of time between periods. Menstrual bleedings are usually lasting from 2 – 7 days, with the average being 5 days. There was one study in which is said that at least 30% of women have irregular periods during their childbirth years.  In the most cases irregular cycle is not a problem but also there are some cases in which it can be a signal of health complications.
Causes of irregular periods: If you have an imbalance of the hormones oestrogen and progesterone or if you have changed your method of contraception, then your menstrual cycle can be disturbed. It is not unusual to have a hormone imbalance for a few years before the menopause and after puberty. This can cause your menstrual cycle to become shorter or longer. Also your periods can become heavier or lighter. If you have irregular periods which are caused by age – related factors, then you will not need to see your doctor.
Here are some causes for irregular menstruation:
- Lifestyle: Stress, excessive exercise and extreme weight loss or weight gain are lifestyle factors which can upset your balance of hormones and also it can cause you irregular bleeding. [1,3]
- Contraceptives: A contraceptive pill or IUS (intrauterine system) may cause spotting between periods. An IU (intrauterine system) does not cause irregular periods but it can cause painful bleeding or heavy bleeding. Small bleeds which are also known as breakthrough bleeds are very common condition when the contraceptive pills are first used. They are usually shorter and lighter than the normal periods and they usually stop within the first few months. 
- PCOS (polycystic ovary syndrome): This condition is happening when very small cysts (which are small and fluid – filled sacs) are developing in the ovaries. The usually symptoms of polycystic ovary syndrome are light periods, irregular periods or no periods at all. Women who suffer from PCOS have ovulation (which is the release of an egg) may not take place as often as normal. Also the production of hormones can be unbalanced and in this condition you can have higher levels of testosterone than normal. Testosterone is a male hormone and women usually have a small amount of it. 
- Gynaecological problems: Problems with the ovaries or womb, early miscarriage and unsuspected pregnancy can be also factors for irregular bleeding. Your doctor may refer you to a gynaecologist which is a specialist in conditions of female reproductive system) because he or she will make further investigation and treatment.
- Thyroid disorders: A thyroid disorder is another possible but rare cause for the irregular menstruation. Thyroid gland is found in the neck. This gland is producing hormones which maintain the body’s metabolism. This is meant for the chemical processes which your body is using to turn the food into energy. Your doctor may test you for thyroid problems by taking a blood test to check the levels of thyroid hormones that are found in your blood. 
- Stress: Chronic stress or in some cases the short – term anxiety about a specific problem can wreak havoc with your hormone balance and they can cause a missed periods and irregular cycle. 
 Wang S, Zhang Z, Liu Y. Effects of exercise intervention on the improvement of polycystic ovary syndrome. 2019. Retrieved from www.intechopen.com/books/polycystic-ovarian-syndrome/effects-of-exercise-intervention-on-the-improvement-of-polycystic-ovary-syndrome
 Ernst H. Getting pregnant with irregular periods: What to expect. 2018. Health Line. Retrieved from www.healthline.com/health/pregnancy/irregular-periods-and-pregnancy
 Ko KM, Han K, Chung YJ, et al. Association between body weight changes and menstrual irregularity: The Korea National Health and Nutrition Examination Survey 2010 to 2012. Endocrinology and Metabolism (Seoul). 2017;32(2):248–56.
 Tolley E, Loza S, Kafafi L, Cummings S. The impact of menstrual side effects on contraceptive discontinuation: Findings from a longitudinal study in Cairo, Egypt. International Perspectives on Sexual and Reproductive Health. 2005. Retrieved from www.guttmacher.org/journals/ipsrh/2005/03/impact-menstrual-side-effects-contraceptive-discontinuation-findings
 Harris HR, Titus LJ, Cramer DW, Terry KL. Long and irregular menstrual cycles, polycystic ovary syndrome, and ovarian cancer risk in a population-based case-control study. International Journal of Cancer. 2017;140(2):285–91.
 Shah MS, Patange RP. A study of correlation between thyroid disorders and menstrual disorders in reproductive age group. Retrieved from pharmascope.org/ijrps/article/view/2433/4833#info
 Nagma S, Kapoor G, Bharti R, et al. To evaluate the effect of perceived stress on menstrual function. Journal of Clinical and Diagnostic Research. 2015;9(3):QC01–QC03.