Awesome Anatomy

This factsheet aims to educate women about the different phases of the menstrual cycle so they have a better understanding of how their bodies work and of menstruation generally.

The menstrual cycle consists of a number of bodily changes associated with the development of an egg and the possibility of pregnancy. The cycle starts with the first day of the menstrual period (referred to as day 1) and ends the day before the next period starts. While the length of the menstrual cycle is often 28 days, menstrual cycles can vary anywhere from 20 days to 40 days. Cycles longer than six weeks are considered unusual.

The length of a woman’s menstrual cycle may change through different life stages. Irregularities are common during adolescence and in the time approaching menopause. Psychological factors such as stress and emotional distress, changes in weight, excessive physical activity and travelling can also cause irregularities in a woman’s menstrual cycle.



Phases of the cycle

There are four distinct phases of the menstrual cycle: menstruation, follicular phase, ovulation and the luteal phase. In order to properly understand menstruation it is necessary to first explain the other phases.

Follicular phase

The follicular phase is the time from the first day of menstruation to ovulation. During this phase the follicle-stimulating hormone (FSH) is released by the pituitary gland. FSH causes between 10 and 20 follicles to begin developing in the ovary. The developing follicles produce the female 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 of these follicles will mature to become the egg (ovum), with the others degenerating. The follicular phase can vary considerably in length, depending on the time of ovulation.

Ovulation

The rise in oestrogen during the follicular phase leads to the secretion of the gonadotropin-releasing hormone (GnRH). This in turn increases the pituitary gland’s production of both the luteinising hormone (LH) and FSH. The abrupt rise in the LH triggers ovulation, which is the release of the egg from the ovary. Following ovulation the egg is swept into the fallopian tube and moved along towards the uterus. If fertilisation does not occur the egg will disintegrate over the next 6 to 24 hours.

Luteal phase

This phase is the time from ovulation to the beginning of menstruation. During this phase the remnants of the follicle from which the egg was released become the corpus luteum. The corpus luteum secretes large amounts of the hormone progesterone and some oestrogen. These hormones contribute to the further thickening and maintenance of the lining of the uterus. If fertilisation does not occur the corpus luteum begins to degenerate and progesterone levels decline leading to the disintegration of the lining.

Women may experience other bodily changes during this phase, including tender or lumpy breasts, fluid retention and bloating. Mood swings, tiredness and feelings of anxiety, anger and sadness can also be common at this time.

Menstruation

Menstruation occurs when the broken down lining of the uterus flows out through the vagina.

Phases of the menstrual cycle



Facts about ovulation

There are several bodily changes that signal the occurrence of ovulation, including differences in cervical mucus and in the position and opening of the cervix.

Cervical mucus and position

Throughout a woman’s cycle the cervix produces mucus, which varies considerably in consistency. Prior to ovulation the cervical mucus becomes clear and slippery, resembling the consistency of raw egg white. The mucus is also very elastic and can be stretched into a string between two fingers. When this type of mucus is present a woman is considered fertile (it is often referred to as ‘fertile mucus’). The texture of the fertile mucus assists and nourishes the 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 the cervical mucus differs in colour and texture. It may be sticky, crumbly, gummy, creamy (like lotion) and white, milky or yellow in colour (2). 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 (eg. 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. Around ovulation the cervix moves into a higher position and the opening, or os, widens. Some women may also 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 the time of ovulation.

Time of ovulation

Women often believe that ovulation occurs midcycle. It actually occurs 12-16 days before the next period. So although a woman with a 28 day cycle may ovulate midcycle (between day 12 and day 16), a woman with a 36 day cycle will ovulate between day 20 and day 24. An easy way to approximate the time of ovulation for women with regular cycles 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 life span can be up to 24 hours, but is usually between 6 and 12 hours (3). In contrast, the sperm generally survive for 3 days, but can live for up to 5 days if optimal fertile cervical mucus is present (4). Therefore, pregnancy is possible 3 to 5 days before ovulation and in the 24 hours following ovulation.

By learning the various signs of ovulation women can calculate their fertile and non-fertile days for contraceptive purposes or to optimise the chances of pregnancy. Women interested in charting their cycle should consult someone experienced in the area of fertility awareness and natural family planning. Women under 35 who are experiencing difficulty in conceiving should consult their doctor after 12 months of trying. This time is reduced to 6 months for those 35 and over.
Facts about menstruation

The menstrual flow

The average length of menstruation can vary from 3 to 7 days but for some women it may be shorter or longer. The length can also differ from one menstrual cycle to the next. Menstrual fluid is actually made up of several components other than blood including endometrial cells, cervical mucus and vaginal secretions (5). The amount of menstrual fluid lost also differs between individuals but generally, a woman loses between 50-100ml of fluid (6).

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

Age of first and last period

The average age of menarche (first period) is considered to be between the ages of 11 and 14. Menarche usually occurs a year or two following other puberty related changes like breast development and pubic and underarm hair growth.

Research suggests that the average age of menarche has fallen over the last century, due to a number of factors including improved diet, better health care and possibly the increase in oestrogen-like substances in the environment (eg. pesticides, plastics) (7). It is recommended that if a young woman has not started menstruating 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 (8).

When young women first start menstruating they are often anovulatory (not ovulating) and, therefore, not fertile. Menstruation without ovulation is quite common in the first few cycles of menstruation and can also occur during other life stages such as before menopause. Even though there may be an uncertainty as to whether ovulation has occurred at particular times in life, contraception still needs to be used if one wants to avoid the chance of pregnancy.

Menopause, the cessation of menstruation, typically occurs in the late 40s or early 50s. In the time leading up to the 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.


Sex and menstruation

Some women avoid sexual contact during menstruation for a number of reasons. They may have religious or cultural beliefs that prevent it or they may feel that their menstrual flow is unpleasant or that their partner will be unwilling. However, apart from religious, cultural, and personal beliefs there are few reasons why women should not have sex during menstruation. One consideration is that the risk of transmitting a blood borne infection (like Hep C and HIV) is higher when having unprotected sex at this time.

The Pill and menstruation

A woman who is on the oral contraceptive pill does not ovulate and therefore, will not experience the same cervical mucus changes or have any ovulation pain. Their ‘period’ is not a natural menstruation but more correctly referred to as a withdrawal bleed. A withdrawal bleed occurs when the synthetic hormones are stopped (during the seven days of inactive, sugar pills).

Women taking the Pill can manipulate its use in order to miss or delay a withdrawal bleed so it does not interfere with travel plans, special occasions etc. Women who experience health problems like endometriosis, menstrual migraine and heavy bleeding may routinely use the Pill to reduce the number of withdrawal bleeds they have a year (and, therefore, the number of times they experience symptoms).

If a woman is taking a monophasic pill (a pill that has the same dosage throughout the cycle) she can miss or delay a withdrawal bleed by simply going straight on to the next pill packet, missing the inactive pills. However, women on a triphasic pill (a pill that has different dosages) may experience spotting if they follow the same procedure due to the change in hormone levels at the start and end of the pill packet. Women on triphasic pills are, therefore, advised to discuss how to miss a withdrawal bleed with their doctor.

Women on the Pill may sometimes experience break-through bleeding, particularly in the first few months of commencing the Pill or with a triphasic pill. If a woman has not missed taking any active pills and has a break-through bleed she is still covered contraceptively. She should, however, 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 menstruation after childbirth

The length of time before a woman’s periods return following pregnancy is largely influenced by whether she is breastfeeding or not. The hormone that stimulates milk production, prolactin, also inhibits ovulation and the return of menstruation. Therefore, women who are fully breastfeeding may not menstruate for months or until breastfeeding ends. The return of menstruation in breast feeding mothers depends upon the frequency and duration of breast feeds a day. It is important to note that women will ovulate and, therefore, be fertile before the return of their first period following delivery/breast feeding.

Sanitary protection

Pads

Sanitary pads are made from highly absorbent materials and come in various thicknesses to suit light, medium and heavy flows. Pads generally need to be changed every three to four hours and should be disposed of in a bin or specialised receptacle. They cannot be flushed down the toilet as they will block the plumbing.

Tampons

Tampons are made from compressed cotton and/or cellulose and come in various sizes to suit different menstrual flows. Tampons are preferred by many women because of their smaller and more convenient size and because they are comfortable to wear. Tampons also allow women to go swimming and to wear clothes that are close fitting.

Despite their convenience some women have reservations about using tampons. For instance, some women worry that a tampon will get ‘lost’. This is actually not possible as the entrance from the cervix to the uterus, the cervical opening or os, is so small that a tampon cannot enter it. Tampons do occasionally become ‘stuck’ in the vagina. If this happens, adopting a squatting position or sitting in a warm bath can assist in removing the tampon.

Young women (and parents of young women) also ask whether tampons can be used by virgins. The answer is ‘yes’ because tampons do not break the hymen as it already has a small gap in it which allows the menstrual fluid to flow out. In addition, the hymen is often no longer intact anyway due to normal physical activity. To make insertion easier, first time tampon users may wish to try a mini tampon, use a lubricant such as KY jelly or saliva or use a tampon applicator (available for sale with some tampon brands). If a tampon has been placed correctly a woman should not be able to feel it.

Tampons need to be changed every three to four hours. Parents of girls who are new to using tampons may wish to remind their daughters about changing their tampon regularly. Women should choose a tampon absorbency that suits their menstrual flow (eg. light tampon when flow is light and regular/super tampon when flow is heavier). Tampons should be disposed of in the same way as pads. It is recommended that pads are used overnight as tampons may dry out the vagina and, therefore, increase the risk of toxic shock syndrome.

Toxic shock syndrome

Toxic shock syndrome is a rare illness caused by the toxins released by the bacteria Staphylococcus aureus. It is believed that not changing a tampon for a long time can cause staphylococcal bacteria to rapidly multiply, releasing toxins into the bloodstream. Symptoms include a sudden high fever, a rash similar to sunburn, vomiting, watery diarrhoea, muscular pain and headache (9). Choosing the lowest absorbency tampon necessary, washing hands thoroughly before and after inserting a tampon and changing tampons at least every three to fours hours, can minimise the already low risk of TSS.

Menstrual problems

There are a range of problems that women may experience with their menstrual cycle. Some of the most commonly reported menstrual disorders are amenorrhoea (absence of periods), dysmenorrhoea (painful menstruation), menorrhagia (heavy bleeding), bleeding between periods and premenstrual syndrome.

Amenorrhoea (absence of periods)

Amenorrhoea, (outside of pregnancy), usually occurs as a result of a hormonal disturbance. These disturbances can be caused by a wide range of factors including weight gain or loss, over-exercising, emotional upsets (both good and bad), anxiety or stress, travel, dietary changes and conditions such as polycystic ovary syndrome (10). Quite often amenorrhoea is only temporary, with periods returning in time. Women experiencing amenorrhoea for longer than six months should consult a doctor.

Dysmenorrhoea (painful menstruation)

While some women experience only mild discomfort during menstruation, other women suffer from severe, incapacitating pain. Period pain is more common in adolescents and women in their 20s, but can also occur in older women. Women may get pain a few days before their period or during the first few days of bleeding. Period pain can consist of 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 and diarrhoea are also common. Popular remedies for mild pain include analgesics (painkillers), antiprostaglandins (eg. Nurofen, Ponstan), herbal medicines, warm baths, heat packs, gentle exercise and rest. Treatment for more severe period pain includes the use of antiprostaglandins and oral contraceptives. To be effective at treating pelvic pain, antiprostaglandins need to be taken before the pain starts. Therefore, women should aim to take them the day before their period is expected. If women do not find relief with these treatments they should consult their doctor. A woman may have endometriosis, a condition in the tissue which lines the uterus grows in other parts of the body outside the uterus. For more information on endometriosis see our Endometriosis factsheet.


Menorrhagia (heavy bleeding)

Because it is hard to accurately measure the amount of menstrual fluid loss, defining an amount that constitutes heavy bleeding can be difficult. The degree to which menstruation interferes with everyday functioning can provide a useful guide. Heavy bleeding can be caused by a number of factors including hormonal imbalances, fibroids, polyps or endometriosis. The excessive amounts of blood lost can lead to a woman becoming anaemic. Treatment may include oral contraceptives and other hormonal drugs, the destruction of the endometrium using a variety of methods, or the use of the intra-uterine system (IUS), Mirena.

Bleeding between periods

Bleeding between periods or spotting can be a symptom of a number of conditions including sexually transmitted infections, gynaecological cancer, endometriosis, fibroids 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

Premenstrual syndrome refers to a collection of symptoms that some women experience before each period (11). Symptoms include physical responses like bloating, headaches, tiredness and food cravings and psychological responses like irritability, anger, depression and lowered self-esteem. Women who suffer from premenstrual syndrome find exercise, dietary changes, yoga, relaxation techniques and herbal remedies are helpful in relieving symptoms.