Intermenstrual bleeding refers to the loss of vaginal blood between regular menstrual periods. Although it varies in duration, it is often shorter than normal flow (1).  In medicine, its technical name is "metrorrhagia". It differs from “spotting”, a normal brown discharge in the middle of the cycle resulting from ovulation (2). 

When is it considered intermenstrual bleeding?

Normal female cycles range from 21 to 35 days. In that interval, vaginal bleeding not exceeding 5 days in duration should be present. The pattern repeats until the onset of the stages of menopause (3). 

When a woman faces irregular periods, it is difficult to establish the existence of intermenstrual bleeding. In contrast, any bleeding by women with a regular cycle that does not coincide with the expected menstruation will be considered intermenstrual (4). 

For women using oral hormonal contraceptives, the hormonal balance results from the use of pills. Therefore, all bleeding not coinciding with the placebo or rest week will be considered abnormal (5). 

Afterwards, progressive amenorrhoea during the perimenopause stage will make it more difficult to establish cycles. In any case, any vaginal bleeding in the already established menopause is abnormal (6). 

Most common causes of intermenstrual bleeding 

Different causes can generate off-cycle bleeding. These are the most important (3,4,5): 

• Hormonal changes: fluctuations in oestrogen and progesterone levels may cause the absence of menstruation, metrorrhagia, or heavy menstruation. This is common during both adolescence and perimenopause. 

• Use of hormonal contraceptives: birth control pills, patches, and injections modify the natural cycle. During the first few months of use of a contraceptive method, irregular bleeding is common. 

• Intrauterine devices or IUD: intermenstrual bleeding is a side effect. 

• Genital tract diseases: pelvic inflammatory disease (PID), vaginitis, and sexually transmitted infections (STI) can cause bleeding. 

• Alterations in the anatomy of the uterus: polyps, fibroids, myxomatosis, and cervical cancer can affect the functions of the uterus. Sometimes, abnormal bleeding is the first telltale symptom. 

• Systemic diseases: especially, coagulation disorders affect female bleeding. 

• Lifestyle changes: periods of stress, the beginning of exercise routines, or more extreme diets can alter the menstrual cycle. 

• Endometriosis: this is a condition in which the tissue that normally lines the inside of the uterus grows outside of it. One of its symptoms is bleeding between periods, along with pelvic pain. 

Finally, it is worth clarifying that pregnancy could be misleading because implantation bleeding is sometimes confused with irregular menstruation. It appears a few days before the expected date and is due to the arrival of the embryo in the endometrium (7). 

Why does it happen in perimenopause? 

Even if you do not know well what is perimenopause, intermenstrual bleeding may surprise you as you go through it. Ultimately, the hormonal changes of this stage affect menstrual cycles (8). 

During perimenopause, anovulatory cycles are common, which means that an egg is not released during this period. Such a lack of release can result in changes in hormone levels (8). 

In addition, as your age increases, oestrogen and progesterone levels decrease. This is also one factor that contributes to the loss of bleeding regularity (9). 

What may you do if you bleed between periods? 

If you experience intermenstrual bleeding, it is important to consult a healthcare professional. Regardless of the cause, it is key to get a proper diagnosis (5). You can help your doctor if you record your symptoms. How long did the bleeding last? In what quantity? These are useful facts to share in your consultation (3). 

Also, review your medical and medication histories, as well as all lifestyle changes. Consider any recent variation: Have you started new contraceptives? Are you going through a period of stress? Did you suddenly change weight? (10) 

Even if you are in the perimenopause stage or already have menopausal symptoms, bleeding between periods may not always be normal. This is especially true if there is persistence of the flow month after month, the amount is abundant, and it is not limited to a few days (6,8).  

We certainly encourage you to do not miss out on consulting a health professional. At the doctor's office, you will be able to clear up your doubts, detect alterations in time, or corroborate that you are only in a passing stage. 

Bibliographic references 

1. Mayo Clinic Staff. Vaginal bleeding definition. [Internet]. Mayo Clinic. 2023 [cited 2024 Mar 2]. Available from: https://www.mayoclinic.org/symptoms/vaginal-bleeding/basics/definition/sym-20050756 
2. Jacobson MH, Howards PP, Kesner JS, Meadows JW, Dominguez CE, Spencer JB, et al. Hormonal profiles of menstrual bleeding patterns during the luteal-follicular transition. J Clin Endocrinol Metab [Internet]. 2020 [cited 2024 Mar 2];105(5):e2024-31. Available from: https://academic.oup.com/jcem/article/105/5/e2024/5770955 
3. Medline Plus. Vaginal bleeding between periods [Internet]. National Library of Medicine of U. S. 2023 [cited 2024 Mar 2]. Available from: https://medlineplus.gov/ency/article/003156.htm 
4. American College of Obstetricians and Gynecologists. Abnormal Uterine Bleeding FAQs. [Internet]. ACOG. 2023 [cited 2024 Mar 2]. Available from: https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding
5. National Health System. What causes bleeding between periods [Internet]. nhs.uk. 2023 [cited 2024 Mar 2]. Available from: https://www.nhs.uk/common-health-questions/sexual-health/what-causes-bleeding-between-periods/
6. National Health System. Postmenopausal bleeding [Internet]. nhs.uk. 2023 [cited 2024 Mar 2]. Available from: https://www.nhs.uk/conditions/post-menopausal-bleeding/
7. National Health System. Vaginal bleeding [Internet]. nhs.uk. 2021 [cited 2024 Mar 2]. Available from: https://www.nhs.uk/pregnancy/related-conditions/common-symptoms/vaginal-bleeding/
8. Dreisler E, Frandsen CS, Ulrich L. Perimenopausal abnormal uterine bleeding. Maturitas [Internet]. 2024 [cited 2024 Mar 2];184(107944):107944. Available from: http://dx.doi.org/10.1016/j.maturitas.2024.107944
9. Verrilli L, Berga SL. What every gynecologist should know about perimenopause. Clin Obstet Gynecol [Internet]. 2020 [cited 2024 Mar 2];63(4):720-34. Available from: https://www.ingentaconnect.com/content/wk/cobg/2020/00000063/00000004/art00006
10. Akhila G, Shaik A, R. Dinesh Kumar. Current factors affecting the menstrual cycle. Int J Res Pharm Hos & Clin Pharm [Internet]. 2020 [cited 2024 Mar 2];2(1):18-21. Available from: https://www.rubatosis.org/journals/index.php/ijrhcp/article/view/165