The Menstrual Cycle

The Menstrual Cycle

The menstrual cycle, all you need to know

The menstrual cycle is a natural cycle experienced by most women. It starts when a girl reaches puberty and continues on until the menopause at around 50 years old. The menstrual cycle runs from the first day of a woman's period and ends the day before her next period. Typically, it is a 28-day cycle, although the cycle length can be longer or shorter than this.

Understanding the menstrual cycle is important for women going through it, and can also be valuable knowledge for any romantic partners when the couple wishes to avoid pregnancy.

What is the menstrual cycle?

The menstrual cycle is a biological process, taking place in women of reproductive age. Essentially, it is your body's process of preparing for a baby and then clearing itself out if those preparations are not needed.

Usually, the menstrual cycle lasts for approximately 28 days. Some women will have shorter cycles, some will have longer cycles, and others may have unpredictable cycles that vary from month to month.

The menstrual cycle is controlled by hormones. Every cycle, the uterus lining thickens in preparation for pregnancy. An egg is released during ovulation and makes its way to the uterus. If you don't become pregnant, the lining sheds and is removed through a menstrual period.

Girls can begin their menstrual cycles anywhere from the age of 10 onwards. However, the average age for girls to start their period is 12 years old. Typically, a woman will have around 480 periods between the ages of 12 and 52, if pregnancy does not occur. If you have one or more pregnancies, this number will be less.

What are the phases of the menstrual cycle?

There are four phases of the menstrual cycle. Typically, the cycle is measured from the first day of

your period or menstruation:


During this phase, the lining of the uterus (also known as the endometrium) is shed. It leaves the body through the vagina, in a fluid that comprises of endometrial cells, mucus, blood and water.

For most women, this phase lasts for between 3 and 7 days.

Follicular phase

This phase starts alongside menstruation and ends at the point of ovulation. Hormones cause the ovary to produce between 5 and 20 ovarian follicles. Each of these ovarian follicles will house an egg and, usually, just one dominant follicle will mature. The same hormones cause the lining of the uterus to start to thicken once again.


Usually happening halfway through the cycle, around day 14, ovulation is the process of an egg being released by the ovary. This egg will travel along the fallopian tube, making its way to the uterus. If it doesn't make contact with sperm within approximately 24 hours, the egg will die.

Luteal phase

The follicles on the ovary, during the final two weeks of the cycle, will transform into corpus luteum. This produces hormones that will keep the lining in place in the uterus, until the body can fully register any potential pregnancy.

If an egg has been fertilised, it will implant in the lining of the uterus. At this point, it produces its own hormones to maintain the corpus luteum. That way, the lining will remain in the uterus throughout the pregnancy. If an egg is not fertilised, the corpus luteum withers at around day 22. Once the corpus luteum has died and stopped producing hormones, the lining of the uterus sheds.

Periods can affect women in many different ways; some women may suffer from very heavy periods and period pains, while others may not be affected by their period. There are a range of products that women can use to ease period pains such as Feminax Ultra (currently out of stock, Naproxen 250mg is a recommended alternative for period pain treatment) and Mefenamic Acid.

What happens during ovulation?

The ovulation process occurs approximately 24 hours after a surge in luteinizing hormone (LH).

Ovulation is the release of an egg from an ovary, where it has matured over the previous two weeks.

The whole process is carefully controlled by the body's hormones. It is the luteinizing hormone that triggers the release of the egg.

Immediately following ovulation, the egg will begin its journey. It travels along the fallopian tube, making its way towards the uterus. It will stay alive for only 24 hours, and must be fertilised during this time to result in a pregnancy.

If you are trying for a baby, sperm must move up the uterus and into the fallopian tubes, where it can meet the egg, within one day of ovulation. While an egg can survive for only 24 hours, sperm can survive a bit longer. Some will last up to five days within the uterus and fallopian tubes, which means that you could get pregnant from intercourse within a window of up to six days.

The ovulation phase will be delayed or stopped if you have taken the morning after pill such as ellaOne. This is to prevent the release of the egg and stop pregnancy.

How can I track my menstrual cycle?

There are many reasons that you might want to track your menstrual cycle. If you are trying to conceive, you can track your cycle to find your most fertile signs. You may also want to track your cycle in order to monitor your health, manage weight loss expectations, or simply so that your period never takes you by surprise.

Using a mobile phone app

You can track your menstrual cycle using a mobile phone app. Menstrual cycle apps allow you to mark on a calendar the first day of your menstrual period. Over multiple months, you will be able to calculate how long each cycle lasts. This is the amount of time from the start of one period to the start of the next.

These apps will use your cycle to calculate your likely day of ovulation. They can also be used to work out what's described as your 'fertile window' - the days to have intercourse if you are trying for a baby.


Using a thermometer can help you to track your menstrual cycle. Your temperature should increase very slightly (up to 1.0°C) during the luteinizing hormone surge. You won't notice this without a thermometer, but may discover a pattern if you check your temperature daily.

Pen and paper

If you don't want the fancy functionality of a period tracking app, then you can do the same with any diary or calendar. Simply mark the first day of your period on your calendar or diary each month, to quickly build up a clear understanding of how long your menstrual cycle lasts.

It is important to note that all forms of tracking are slightly inaccurate. Even a tracking app, with its functions and calculations, won't get all the details right. The human body is unpredictable, and it is important not to rely on menstrual cycle tracking as a form of birth control or contraception.

Even outside your assumed fertile window, pregnancies can still occur. Your body may release an extra egg one month, or you might have an unusual cycle with ovulation happening earlier or later than normal.

Tracking your cycle can help you to increase your chance of pregnancy, and to quickly identify any unusual months that might be signs of a health concern, but cannot be relied upon as an alternative to proper contraception.

By tracking your menstrual cycle, you can also identify if your period is due to come at an inconvenient time. If that is the case, there are a number of medicines to stop your period for a certain amount of time. For example, women may choose to delay their periods if they are going on holiday or getting married.

When does the menstrual cycle stop?

The term ‘menopause’ is the medical diagnoses used to describe the years when a woman’s ovaries gradually start to produce less eggs and fewer female hormones, such as oestrogen and progesterone.

The reduction in these hormones will mean that periods will become less regular and will gradually stop altogether. This process can produce many symptoms and conditions in women, which is why it is common for women to be prescribed hormone replacement therapy medications. Hormone replacement therapy involves replacing the hormones that were previously produced by the ovaries in order to reduce symptoms related to a natural drop in these hormones.

Frequently asked questions

What are the 4 stages of the menstrual cycle?

The menstrual cycle lasts from the first day of a woman's period and ends the day before her next period. Typically, this is a 28-day cycle.

The four phases of the menstrual cycle are:


Most women will experience this period for between 3 and 7 days.

During menstruation, the lining of the uterus (endometrium) is shed. It exits the body through the vagina via a fluid that is comprised of endometrial cells, mucus, blood and water.

Follicular phase

The follicular phase begins at the same time as menstruation and ends at the time of ovulation, when an egg is released. Follicle stimulating hormone is released by the pituitary gland into the bloodstream. It stimulates the growth of ovarian follicles in the ovary before an egg is released during ovulation.

Hormones cause the ovary to produce between 5 and 20 follicles, each of which houses an egg. However, in most cases only one follicle will mature. These hormones are also responsible for the lining of the uterus starting to re-thicken.


Ovulation normally occurs halfway through the menstrual cycle. This process is where an egg is released by the ovary. The egg travels along the fallopian tube until it reaches the uterus. A fertilized egg can result in pregnancy, but if the egg has not made contact with sperm within approximately one day, it will die.

Luteal phase

During the final two weeks of the menstrual cycle, the follicles on the ovary will transform into corpus luteum. This produces hormones that keep the lining within the uterus in place, until your body can register a potential pregnancy.

If an egg is fertilised, it will implant itself in your uterus's lining, where it will produce its own hormones to maintain the corpus luteum. This keeps the lining in the uterus throughout pregnancy.

If an egg has not been fertilised, the corpus luteum will die on around the 22nd day of the menstrual cycle. The lining of the uterus sheds once the corpus luteum has died and is no longer producing hormones.

Some women may experience heavy menstrual bleeding and period pains, while some may not suffer.

How many days after a period is the next period?

The average menstrual cycle lasts for approximately 28 days. Therefore, about 28 days pass between the first day of one period and the first day of the next period.

This is not set in stone; some women may find that their periods happen in a shorter time, such as 21 days. In some women, their periods occur every 35 days.

What is a normal menstrual cycle?

The average length of a woman's menstrual cycle is 28 days. However, there is no set time frame as the length of the cycle can vary from person to person and based on their own individual womens health.

Some women may find that they get their period every 21 days, while some may take as long as 35 days.

The menstrual cycle has four phases: menstruation, follicular phase, ovulation and luteal phase. More information on each phase can be found on the main blog.

How do you count your menstrual cycle?

To work out how long your cycle is, start on the first day of your last menstrual cycle and begin counting (cycle day 1, 2, 3, etc.). The length is the last cycle day before menstruation begins.

If your last period started on the 1st March and your next period began on the 31st March, this would mean that your period comes, on average every 30 days. However, it is important to remember that the menstrual cycle can vary in length.

Why should I keep track of my menstrual cycle?

If you have regular periods, tracking them will help you to know when you are due to ovulate, when you are most likely to get pregnant and when you can expect to start your next period.

If you have irregular periods, keeping a track of them will allow you to speak to your doctor or nurse about any problems.

If you are suffering from period pain or any bleeding which makes you miss work or school, tracking your symptoms will make it easier for a doctor or nurse to provide medical advice and find a treatment that is suitable. If you have any severe bleeding or pain that makes it difficult to carry out everyday tasks, this is not a normal part of the menstrual cycle. However, it can be treated.

What is menstruation?

Menstruation, also referred to as a period, is a woman's monthly bleeding.

A woman's menstrual flow discards the monthly build-up of uterine lining. The menstrual flow includes blood and tissue from the uterus, which flows from your uterus through the small opening in the cervix. This then passes out of the body through the vagina.

During a monthly menstrual cycle, the uterine lining builds up to prepare the body for pregnancy. If a woman does not become pregnant, the oestrogen and progesterone levels begin to fall. Low hormone levels of progesterone and oestrogen will then result in menstruation.

What is a normal amount of bleeding during my period?

On average, a woman will lose about two to three tablespoons of blood when she is having her period. Some women may have bleeding which is lighter or heavier than this amount, but this should not be a cause for alarm; what is a normal amount of blood for one woman may be different for another. The flow may also be slightly heavier or lighter from month to month.

As women age, their periods can change. During the transition to menopause (the perimenopause), some women may experience heavy bleeding.

Heavy menstrual bleeding symptoms include:

  • Bleeding that lasts for longer than 8 days
  • Passing large blood clots
  • Bleeding through one or more tampon or pad every one to two hours

When does a girl usually get her first period?

The average age for a girl to get her first period is 12 years old, but that may not be the case for all girls.

Women's menstrual cycles may start at any time between the ages of 8 and 15. Normally, a girl will get her first period around two years after her breasts have started to develop and pubic hair has started to grow.

A girl should speak to a doctor if:

  • Her periods begin before the age of 8
  • She is 15 and her period has still not started
  • She has not had her first period within three years of breast growth

How does the menstrual cycle change as I get older?

As a woman ages, her menstrual cycle can change in various ways. It is not unusual for periods to be heavier when women are in their teenage years, getting lighter as they get into their 20s and 30s.

For the first few years after you have your first period, it is normal for menstrual cycles to last for longer than 38 days. A girl is likely to have more regular cycles within three years of their periods beginning. If you are still suffering from longer or irregular periods after this time, you should speak to your doctor.

Women in their 20s and 30s will normally have regular cycles, which may last from anywhere between 24 and 38 days.

Women in their 40s may find that their cycles are more irregular. This is due to hormonal changes in the body as it transitions into the menopause. Periods may stop for one month or longer, before starting again. Your periods may also be shorter or longer, heavier or lighter. Women who are going through these changes should seek medical advice if their menstrual cycle length is longer than 38 days or shorter than 24 days.

What is ovulation?

The process of ovulation is when the ovary releases an egg to be fertilized by sperm to achieve pregnancy. Women are more likely to get pregnant if they do not use birth control and have sex in the three days before and up to the day of ovulation.

Male sperm is able to survive within the female reproductive system for between 3 and 5 days. However, after a woman has ovulated, her egg can only survive for between 12 and 24 hours after this. A fertilized egg leads to pregnancy.

The length of a woman's cycle can differ. The time between ovulation and the next period beginning can range from between 7 days and 19 days.

Ovulation stops occurring at various points in a woman's lifetime:

  • Pregnant women will not ovulate.
  • Women may not ovulate if they are breastfeeding. Speak to your doctor about birth control methods if you are breastfeeding and wish to avoid another pregnancy.
  • Women who are transitioning to the menopause may not ovulate every month.
  • Women do not ovulate after they have been through menopause.

How do I know if I am ovulating?

The vaginal mucus or discharge will become clearer and slipperier a few days before you start ovulating. This mucus is what helps the sperm to move up into the uterus and into the fallopian tubes to fertilize a released egg. When some women ovulate, they feel a minor cramp on one side of their pelvic area.

Luteinizing hormone is released by the brain to tell the ovary to release an egg. The hormone levels begin to rise for about 36 hours before you ovulate. These hormone levels will peak about 12 hours before you ovulate. If a woman is trying to get pregnant and is tracking her ovulation, she will notice a rise in her temperature when she wakes up but before getting out of bed, around the time she ovulates.

How often should I change my pad, tampon, period panties, sponge or menstrual cup?

Whichever of these products you use for your periods, you must follow the instructions that come with them carefully.

Always try to change or rinse your period product before it is full.

As a general rule of thumb:

  • Pads are changed every few hours by most women
  • Tampons should not be worn for longer than 8 hours (this may cause toxic shock syndrome)
  • Period panties can normally last for a day, depending on the style and your menstrual flow
  • Sponges and menstrual caps might only need rinsing one or two times a day

It is quite normal for women to use different products for each phase of their period, depending on how light or heavy the bleeding is in each phase.

What is toxic shock syndrome?

Toxic shock syndrome is a serious condition that is caused by bacteria which creates toxins and poisons. Thankfully, it is a very rare syndrome, but it can be deadly. A particular brand of super-absorbency tampons was believed to be the cause of this problem, when 63 women died from toxic shock syndrome in 1980. This product was subsequently taken off the market.

Most cases of toxic shock syndrome are not currently caused by using tampons. Nonetheless, if you use more absorbent tampons than you need for the bleeding you are experiencing, or if you do not change your tampon every four to eight hours, you may be at risk of developing this condition. Women who use products that need to be inserted into the vagina, such as menstrual cups, cervical caps or sponges, may also be at a risk of toxic shock syndrome if they are left in the vagina for too long.

Symptoms you may be suffering from toxic shock syndrome include:

  • Rash
  • Diarrhoea
  • High fever
  • Muscle aches
  • Nausea and/or vomiting
  • Kidney or other organ failure

Anyone who believes they may be suffering from this condition should seek medical attention immediately.

What causes menstrual cycle irregularities?

There are various different causes for irregularities in a woman's menstrual cycle. These can include:

  • Premature ovarian failure: (the loss of normal ovarian function before a woman is 40). Also known as primary ovarian insufficiency, women with this condition may have irregular or only occasional periods for years.
  • Missing a period may be a sign of early pregnancy. If a woman is breastfeeding, her period is generally delayed after being pregnant.
  • Uterine fibroids can cause heavy periods and also prolong menstrual periods.
  • Excessive exercise, extreme weight loss or eating disorders can disrupt the menstrual cycle.
  • Women who suffer from polycystic ovary syndrome (PCOS) may have irregular periods. They may also suffer from enlarged ovaries which contain small amounts of fluid.
  • Pelvic inflammatory disease (PID), which is an infection in the reproductive organs, may cause irregular bleeding during a woman's period.

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