Understanding your menstrual cycle fact sheet


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The term ‘menstrual cycle’ refers to the changes that occur naturally in a woman’s body to prepare it for pregnancy.

In a normal menstrual cycle, women experience menstruation (also known as a period) followed by the release of an egg. During menstruation blood, cells and mucus are discharged from the uterus.

The menstrual cycle starts on the first day of the menstrual period (referred to as day one) and ends the day before the next period begins. While the length of the menstrual cycle is often 28 days, it can vary between women and from one cycle to the next. It is common for women to experience cycles that last anywhere from 20 to 40 days. Cycles longer than six weeks are considered unusual.

The length of a women’s menstrual cycle can change throughout her life. Irregular periods are common among adolescent women, and in women approaching menopause. Factors such as stress, extreme emotion (good or bad), weight changes, excessive physical activity and travelling can also cause irregularities in a woman's menstrual cycle.

Phases of the menstrual cycle

The menstrual cycle has four distinct phases: menstruation, the follicular phase, ovulation, and the luteal phase.

Four different phases of the menstrual cycle

Although menstruation is considered to be the first phase of the cycle, in order to properly understand menstruation, it is necessary to first explain the other phases.

During this phase, the pituitary gland releases follicle-stimulating hormone (FSH), which causes between 10 and 20 follicles (cells that contain immature eggs, known as ova) to begin developing in the ovary. They produce the hormone oestrogen, which causes the lining of the uterus (endometrium) to become thick in preparation for the possible embedding of a fertilised egg (1).

Usually only one follicle develops into a mature egg (2). This follicle moves towards the surface of the ovary, while the others break down and are reabsorbed by the body. The follicular phase begins on the first day of menstruation and ends with ovulation. It can vary considerably in length, depending on the time of ovulation. 

The term ‘ovulation’ refers to the release of a mature egg from the ovary. During the follicular phase, the rise in a woman’s oestrogen levels causes gonadotropin-releasing hormone (GnRH) to be released from her brain. This in turn causes the pituitary gland to produce increased levels of luteinising hormone (LH). The abrupt rise in LH, known as the LH surge, triggers ovulation. Following ovulation, the egg is swept into the fallopian tube and moved along towards the uterus. If fertilisation does not occur, the egg disintegrates within 6-24 hours.

Cervical mucus and position
Just before ovulation, a woman’s cervical mucus becomes clear and slippery, resembling raw egg white; it is very elastic and can be stretched into a string between two fingers. This kind of cervical mucus is known as 'fertile mucus' because a woman is considered fertile when it is present. Fertile mucus assists and nourishes sperm as they travel up the vagina towards the opening of the cervix.

When a woman is in a non-fertile phase of her cycle, her cervical mucus differs in colour and texture. It might be sticky, crumbly, gummy or creamy (like lotion) in texture, and white, milky or yellow in colour (3). This mucus cannot be stretched between the fingers and may have a sour smell. It is important to note that secretions related to sexual arousal, semen, lubricants, spermicides, vaginal infections (e.g. thrush), and certain medications can all interfere with the appearance of cervical mucus.

The positioning of the cervix and its opening also change throughout a woman's cycle. At about the time of ovulation, the cervix moves into a higher position and its opening widens. Some women may experience aches or pain around the time of ovulation. This pain can vary from cramps or a general ache in the abdomen to sharp pains in one side. Spotting (light bleeding) can also occur at this time.

Time of ovulation
Women often believe that ovulation occurs mid-cycle. It actually occurs 12-16 days before the next period starts. So, although a woman with a 28-day cycle may ovulate mid-cycle (between day 12 and day 16), a woman with a 36-day cycle will ovulate between day 20 and day 24.

For women with regular cycles, an easy way to approximate the time of ovulation is to subtract 16 from the number of days in the cycle and then add 4. This will calculate the span of days in which ovulation is most likely to occur. For instance, a woman with a 22-day cycle is most likely to ovulate between days 6 and 10 of her cycle (22-16 = 6 (+4 =10).

Ovulation and conception
Following ovulation, the egg's lifespan can be up to 24 hours, but is usually between six and 12 hours (4). In contrast, sperm generally survive for three days, but can live inside the vagina for up to five days if optimal fertile cervical mucus is present (5). Pregnancy can therefore result from intercourse that occurs within a woman’s fertile window (from as early as five days before ovulation, until up to 24 hours following ovulation).

During this phase, the remnants of the follicle that released the egg (now called the corpus luteum) release large amounts of the hormone progesterone as well as some oestrogen. These hormones contribute to the further thickening and maintenance of the uterine lining. If fertilisation does not occur, the corpus luteum breaks down and progesterone levels decline, leading to the disintegration of the uterus lining. During the luteal phase, women may experience physical and emotional changes including tender or lumpy breasts, fluid retention, bloating, mood swings, tiredness or anxiety (see Premenstrual syndrome).

Menstruation occurs when the broken-down lining of the uterus flows out through the vagina. Menstruation generally lasts from three to seven days. Some women regularly have periods that are shorter or longer than this. The length can also differ from one cycle to the next. In addition to blood, menstrual fluid is made up of several components including endometrial cells, cervical mucus and vaginal secretions (6). The amount of menstrual fluid lost varies between women and from one cycle to the next, but a woman generally loses about 50-100ml of fluid each time she has a period (7).

Menstrual flow may be heaviest or lightest at the beginning of menstruation or may change throughout. The colour can range between black, brown, dark red, bright red and pink. Menstrual fluid only tends to have an unpleasant odour after it has been in contact with air for a period of time.

Age of first and last period (menarche and menopause)
In Australia, menarche (the onset of menstruation) occurs most often in girls aged from 11 to 14. Menarche usually occurs a year or two following the appearance of other puberty related changes, such as breast development and pubic/underarm hair growth. Genetic factors and social influences, as well as a girl’s ethnicity, size, and weight, can influence when menarche occurs (8). Girls with a higher body mass index (BMI) are likely to begin getting periods earlier than those with lower BMI scores (9). Girls who are highly physically active (such as athletes) tend to have slightly delayed menarche.

Research suggests that the average age of menarche has fallen during the last century. This can be attributed to a number of factors including improved nutrition, better healthcare and possibly the increase in oestrogen-like substances in the environment (e.g., pesticides and plastics) (10). Recent studies suggest that the age of menarche is often slightly reduced in girls who are subject to emotional stressors, such as family disruption or childhood adversity, and in girls who consumed high intakes of animal proteins, such as cow’s milk, during childhood (11).

It is recommended that if a young woman has not had her period by the time she is 16, she should consult a doctor to ensure that she does not have a medical condition that is preventing menstruation from occurring (12).

When young women first start menstruating, they are often anovulatory (not ovulating) and, therefore, not fertile. However, it is important for sexually active young women to remember that as soon as they start menstruating, pregnancy can occur. Therefore, they should use contraception if they wish to avoid becoming pregnant.

Menstruation without ovulation can also occur at other life stages, such as before menopause. Menopause, the ending of periods, typically occurs in women who are in their late 40s or early 50s. In the time leading up to menopause, the menstrual cycle and/or flow may change, becoming lighter, heavier or longer. While irregular bleeding is also common at this time, it can be a symptom of gynaecological cancer so women experiencing this should consult their doctor. Even though women may be unsure as to whether they are ovulating prior to menopause, contraception still needs to be used if pregnancy wants to be avoided.

Sex and menstruation
Some women avoid sexual activity when they have their period for personal, cultural or religious reasons. However, there are few physical reasons why women should avoid sex during menstruation. One consideration is that the risk of transmitting blood-borne infections such as hepatitis C and HIV is higher when having unprotected sex at this time. It is possible for pregnancy to occur if women have unprotected sex during menstruation. Women who want to avoid pregnancy should use contraception at this time.

The Pill and menstruation
The Pill contains synthetic oestrogen to prevent the development of an egg (and therefore, ovulation), and synthetic progesterone to increase the thickness of cervical mucus (to slow the movement of sperm) and prevent the complete development of the uterine lining.

Women who do not ovulate do not experience changes in cervical mucus or ovulation pain. Their 'period' is actually a withdrawal bleed resulting from the stopping of the synthetic hormones (during the four to seven days of inactive/sugar pills) rather than a natural menstruation.

Women taking the Pill can use it to miss or delay a withdrawal bleed. This can be convenient for women planning travel or special occasions. Women who experience health problems such as endometriosis, menstrual migraine and heavy bleeding may use the Pill to reduce the number of withdrawal bleeds they have a year (and, therefore, the number of times they experience symptoms). Women taking a monophasic Pill (a version of the Pill that delivers the same dosage throughout the cycle) can miss or delay a withdrawal bleed by simply missing the inactive/sugar pills and going straight on to the active hormones in the next pill packet. However, women on a triphasic Pill (a version of the Pill that delivers different dosages throughout the cycle) may experience spotting if they do this, due to the change in hormone levels at the start and end of the pill packet. Women on triphasic Pills who wish to miss a withdrawal bleed should seek advice from their doctor.

Breakthrough bleeding can sometimes occur in women on the Pill, particularly in the first few months of taking it or if the woman is using a triphasic Pill. A woman is still covered contraceptively if she has not missed any active pills and has a breakthrough bleed. However, she should consult her doctor to review the choice of Pill and to ensure the bleeding is not related to another condition (see Bleeding between periods section).

Return of periods after childbirth
The length of time before a woman's period returns following pregnancy largely depends on whether she is breastfeeding or not. This is because the hormone that stimulates milk production, prolactin, also inhibits ovulation and the return of menstruation. Therefore, women who are fully breastfeeding may not have a period for several months after childbirth or until they finish breastfeeding. The return of menstruation in breastfeeding mothers depends upon the frequency and duration of breastfeeds a day.

In women who are not breastfeeding, and women who are combining breastfeeding with bottle feeding, menstruation can return as soon as five-to-six weeks following childbirth. It is important to be aware that women will ovulate, and therefore be fertile, before the return of their first period following delivery/breastfeeding. It is also important to note that even though breastfeeding can delay the return of periods, it is not a reliable form of contraception.

Common menstrual problems

Some of the most commonly reported menstrual problems are an absence of periods, painful periods, heavy bleeding, bleeding between periods, and premenstrual syndrome (PMS).

Outside of pregnancy, amenorrhoea is usually the result of hormonal disturbances. These disturbances can be caused by a wide range of factors including weight gain or loss (body weight and body fat percentage are directly related to ovulation and menstruation), being chronically underweight (16), over-exercising, extreme emotion (both good and bad), anxiety or stress, travel, dietary changes, and conditions such as polycystic ovarian syndrome (17). Often, amenorrhoea is temporary, with menstrual periods returning in time. Women who are not pregnant and have not had a period for longer than six months should consult their doctor.

While some women experience only mild discomfort when they have their period, other women suffer from severe, incapacitating pain. This kind of pain is not normal and women should consult their doctor if the pain they experience interferes with their ability to function normally.

Women might get pain a few days before their period or during the first few days of bleeding. The pain can be a cramping-type pain, caused by the contraction of the uterine muscles, or a heavy dragging pain in the pelvic region. Pain in the legs and back, headaches, nausea, constipation and diarrhoea are also common.

Period pain can be the result of prostaglandins, the substance that causes the uterus to contract during a period. Severe period pain might also signal the presence of conditions such as pelvic inflammatory disease or endometriosis. Popular remedies for mild pain include analgesics (aspirin or paracetamol), warm baths, heat packs, gentle exercise and rest. Treatment for more severe period pain includes the use of antiprostaglandins (e.g., Nurofen, Ponstan) and oral contraceptives. If women do not find relief with these treatments they should consult their doctor.

Because it is hard to measure the amount of menstrual fluid lost, it is difficult to define what constitutes heavy bleeding. However, the degree to which a woman's period interferes with her everyday life can provide a guide (e.g., having to change a pad or tampon every hour can indicate that bleeding is heavy).

Heavy bleeding can be caused by a number of factors including hormonal imbalances, fibroids, polyps, endometriosis, or, less commonly, bleeding disorders. Excessive blood loss through heavy periods can lead to iron deficiency and anaemia.  The Pill and/or antiprostaglandins can be used to treat heavy bleeding.  Other treatment options include inserting a Mirena intra-uterine device (IUD), or undergoing endometrial ablation (a procedure that causes the destruction of the uterine lining)..  

Bleeding or spotting between periods can be a symptom of a number of conditions including sexually transmitted infections, endometriosis, fibroids, gynaecological cancer, or a thyroid disorder. It can also be a side effect of some contraceptives or medications (see The Pill and menstruation section). If a woman experiences bleeding between periods she should consult her doctor.

Premenstrual syndrome (PMS) refers to a number of symptoms some women experience before each period (18). Physical signs of PMS include tender or lumpy breasts, fluid retention, bloating, food cravings and headaches. Psychological signs include mood swings, tiredness, and feelings of anxiety, anger, and sadness. Women who suffer from mild premenstrual syndrome might find exercise, dietary changes, yoga, relaxation techniques, and herbal remedies useful.

A small percentage of women suffer from a severe form of PMS called premenstrual dysphoric disorder (PMDD). Women with PMDD experience symptoms so severe that they greatly impact their everyday functioning. Treatments for PMDD include lifestyle changes, the Pill, cognitive behavioural therapy, and, if other treatments are unsuccessful, a type of antidepressant known as selective serotonin-reuptake inhibitor (SSRI) may be prescribed.

About half of all women who suffer from migraine can clearly link at least some of their attacks to their periods. Some women have migraine attacks only related to their period, not at other times of their menstrual cycle. It is thought that the drop in oestrogen that occurs just before a woman has a period is a migraine trigger. Women who think their migraines may be related to their menstrual cycle are recommended to keep a diary tracking their menstrual cycle and migraine attacks for three months to show to their doctor.


  1. Ojeda, L. (1983). Exclusively Female: A Nutrition Guide for Better Menstrual Health. Claremont: Hunter House, pp2-3
  2. Boston Women's Health Collective. (1998). Our Bodies, Ourselves: For the New Century. New York: Touchstone, p276
  3. Weshler, T. (1995). Taking Charge of Your Fertility: The Definitive Guide to Natural Birth Control and Pregnancy Achievement. New York: HarperCollins, p58
  4. ibid.
  5. Billings, E. & Westmore, A. (1992). The Billings Method: Controlling Fertility Without Drugs or Devices. South Yarra: Ann O'Donovan, pp21-22
  6. Boston Women's Health Collective., op. cit., p278
  7. Grimwade, J. (1995). The Body of Knowledge: Everything You Need to Know About the Female Cycle. Melbourne: William Heinemann, pp21-2
  8. Karapanou, O. & Papadimitriou, A. (2010). Determinants of Menarche. Reproductive Biology and Endocrinology 2010 (8): 115
  9. Ojeda, L., op. cit. p11-12
  10. Sloboda, D. M., Hart, R., Doherty, D.A., Pennell, C.E., & Hickey, M. (2007). Age at Menarche: Influences of Prenatal and Postnatal Growth. The Journal of Clinical Endocrinology and Metabolism92(1):46-50.
  11. Yermachenko, A. & Dvornyk, V. (2014). Non-genetic Determinants of Age at Menarche: A Systematic Review. BioMed research international, 2014, 371583. DOI:10.1155/2014/371583
  12. Donague, K. (1999, April 16). Puberty: When is it too early or too late? Medical Observer, p69
  13. Queensland Health. (2010). For the Girls – Your Vagina. Retrieved November 3, 2014, from www.health.qld.gov.au/istaysafe/girls/your-vagina.aspx
  14. Grimwade, J., op. cit., pp29-30
  15. Royal Adelaide Hospital. (2008). Sexuality and Fertility. Spinal Cord Injury. Retrieved November 4, 2014 from www.rah.sa.gov.au/hampstead/downloads/sascis_chapter8.pdf
  16. Mocanu, V., Luca, V.C., Stoica, A.R., & Zbranca, E. (2001). The influence of body weight upon the function of ovarian axis. Revista medico-chirurgicală a Societăţii de Medici şi Naturalişti din Iaşi. 2001 Jul-Sep;105(3):469-74. Retrieved via PubMed, PMID 12092175.
  17. Grimwade, J., op. cit., p231-9
  18. Grimwade, J., op. cit., p241

For help understanding this fact sheet or further information on menstruation or menstrual problems, women in Queensland can contact the Health Information Line on 3216 0376 (within Brisbane) or 1800 017 676 (toll free).

Last Reviewd: June 2018

Last updated: January 2015

© Copyright Women's Health Queensland Wide. This fact sheet was last updated in January 2015.






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