This website has moved to a new location. Please visit our sister website for next day delivery.
  • Prescription included
  • Genuine medication
  • All-inclusive service - No hidden fees
  • Free next-day delivery
Home / Period Delay / Understanding the menstrual cycle

Understanding the menstrual cycle

Learn about your hormones and the different phases of the menstrual cycle

Having an understanding of the menstrual cycle is beneficial for your overall health. It can help to:

  • know when you’re fertile and ovulating
  • understand your emotions throughout the month, and how your hormones play a role
  • keep track of your periods and have a better idea of when to expect your next bleed
  • feel more in tune with your body

The menstrual cycle consists of four phases, with your period indicating the start of a new cycle. Keep reading to learn how the female reproductive system works and how hormone levels change throughout the month.

What is the menstrual cycle?

The menstrual cycle is the reason women have periods. Every month or so, women and girls release an egg from their ovaries into their womb. This makes it possible to become pregnant.

There are a series of hormones involved in the menstrual cycle. These include:

  • oestrogen
  • progesterone
  • luteinising hormone (LH)
  • follicle-stimulating hormone (FSH)
A graphic of the female reproductive system

The production of these hormones causes changes in the female reproductive system. They are responsible for ovulation and menstrual bleeding, as well as changes in mood and energy levels.

All women and girls who are of reproductive age experience a menstrual cycle. When a woman reaches an age where she stops menstruating, we refer to this as menopause.

How long does a menstrual cycle last?

The length of a menstrual cycle differs from woman to woman. On average, you should get your period every 21-35 days. It is normal to bleed for 2-7 days during menstruation.

If there are less than 21 days or more than 35 days between menstrual bleeds, you may be experiencing irregular periods. These are common too and can be caused by lifestyle factors such as stress or weight loss, or conditions like PCOS (polycystic ovary syndrome).

In many cases, your body gets back on track by itself. However, if your periods are frequently inconsistent and difficult to track, ask your doctor for advice.

How does the menstrual cycle affect fertility?

It is thanks to the menstrual cycle that women can conceive and become pregnant.

Ovulation is a phase of the menstrual cycle where an egg is released from the ovaries. It is also when fertility levels (the ability to get pregnant) are highest.

Sperm cells pointing towards an egg cell

Your body prepares itself before the egg is released, making the perfect conditions for a potential embryo (when an egg cell becomes fertilised by a sperm cell) to become implanted in the womb.

If the egg cell isn’t fertilised, it is discarded from the body during your period.

What are the different phases of the menstrual cycle?

There are four phases in the menstrual cycle. These are known as:

  • menstruation
  • follicular phase
  • ovulation
  • luteal phase
An infographic displaying the four phases of the menstrual cycle


The first day of your period marks the start of a new cycle. Getting your period is called menstruation.

When you menstruate, your uterus lining is shed. This causes blood (as well as vaginal secretions and uterine cells) to exit from your vagina. The bleeding usually lasts around 2-7 days, depending on your flow.

Some women experience abdominal cramps when they menstruate, whereas others might experience little to no discomfort.

Follicular phase

The follicular phase starts on the first day of your period too but carries on for 13-14 days (until ovulation).

During this time, your body starts to produce follicles on the ovaries. Eventually, one of these follicles will mature, causing one of your eggs to be released.

The lining of the womb also thickens at this point in your cycle, in preparation for the egg cell and potential fertilisation.


Once an egg cell has matured, it is released from one of the ovaries (travelling via the fallopian tube) into the womb. This is known as ovulation and usually occurs on day 14 of your cycle (if your cycle is 28 days long).

During ovulation, you are most fertile and have the highest chances of conceiving. If a sperm cell reaches this egg, there is a chance of becoming pregnant.

Luteal phase

After ovulation, you enter the luteal phase, which usually lasts from day 15 until the end of your cycle.

The lining of the womb continues to thicken in preparation for a possible pregnancy. If the egg cell does become fertilised, it will implant into the lining where it will start to develop.

If the egg cell is not fertilised, your body sheds the thickened lining instead. This causes your period and therefore a new cycle.

You might also experience premenstrual syndrome (PMS) during the luteal phase. After ovulation, women often encounter changes in their mood as well as headaches and hormonal acne.

How are hormones involved in the menstrual cycle?

Hormones are chemical messengers that give your body certain signals. In this case, there are 4 hormones responsible for controlling your menstrual cycle:

An infographic displaying the different hormone changes in the menstrual cycle
  • Follicle-stimulating hormone (FSH): FSH is released from the pituitary gland in the brain. When FSH levels rise, it stimulates an egg cell to develop as well as the release of oestrogen.
  • Oestrogen: Oestrogen is mainly released from the ovaries, making it a sex hormone. It causes the lining of the womb to thicken and stimulates LH (so that ovulation takes place).
  • Luteinising hormone (LH): LH is also released from the pituitary gland. It stimulates ovulation (the release of a mature egg) as well as the release of progesterone.
  • Progesterone: Progesterone is produced by the adrenal glands (located at the top of the kidneys) and the ovaries. It’s responsible for maintaining the uterus lining and stopping the release of LH after ovulation.

What factors can impact the menstrual cycle?

Sometimes, your menstrual cycle doesn’t flow like normal. You might be spotting in between bleeds, experiencing irregular periods, or not having a period at all.

Several factors can impact your cycle:

  • Menopause: When women get older their ovaries slowly stop releasing egg cells. This is called menopause. It causes your periods to become less frequent until they stop altogether. It also causes side effects like hot flashes, changes in mood, vaginal dryness and difficulty sleeping.
  • Undereating and fast weight loss: If you’re not eating enough calories, your body won’t have enough energy to produce the right amount of hormones. This can cause menstrual irregularities.
  • Polycystic ovary syndrome: PCOS involves hormone imbalances, like having too many ‘male’ hormones (androgens) in your body. This affects the menstrual cycle and often stops ovulation from happening. As a result, women with PCOS often have infrequent periods or no periods at all.
  • Endometriosis: This is a chronic, life-impacting condition where tissue similar to that of the uterus lining grows outside of the uterus. Women with endometriosis may suffer extreme pain during menstrual bleeds, as well as a much heavier flow.
  • Other chronic health issues: Conditions like diabetes, celiac disease, thyroid disease and Cushing’s disease can all impact the menstrual cycle. Speak to your doctor if you suffer from any of these conditions and are experiencing unusual or irregular periods.
  • Pregnancy: One of the first signs of pregnancy is a missed period. If you become pregnant, your menstrual cycle will be put on hold while the foetus develops in the uterus.

By taking hormonal contraception, you can temporarily protect yourself from becoming pregnant without having to rely on barrier methods like condoms.

How does contraception impact the menstrual cycle?

Hormonal birth control temporarily affects your fertility by changing your hormone levels. This impacts your normal menstrual cycle.

The combined pill contains artificial versions of oestrogen and progesterone. When taken regularly, it stops ovulation and your natural menstruation. Instead of a period, you have a lighter withdrawal bleed every time you take your pill break. When taken correctly, the combined pill is at least 99% Trusted source Better Health Channel Government Source Victorian State Health Department, Australia Go to source effective at preventing pregnancy.

Woman holding a pack of hormonal birth control pills

The mini pill contains an artificial form of progesterone and prevents pregnancy by thickening the cervical mucus (so that sperm can’t enter the womb). In some cases, it also stops ovulation and your natural periods, but this varies from person to person.

It’s also possible to delay your menstrual cycle with the use of Norethisterone. This is another type of hormonal treatment that can be taken on occasion if you’d like to delay menstruation. However, it cannot be used as a method of contraception.

Want to learn about period delay?

Click here
Medically reviewed by Dr. Caroline Fontana Written by our editorial team Last reviewed 25-06-2024
Period Delay

Our service - only on euroClinix
  • Private & confidential serviceDiscreet packaging and encrypted data
  • Genuine & branded medicationFrom UK registered pharmacies
  • No doctor visit neededOur doctors assess you online
  • Free next day deliveryOrder by 4:30 to receive tomorrow
View Treatments

Further reading

How To Delay Your Period

How To Delay Your Period

Reviewed by Dr. Caroline Fontana
What are the causes of irregular periods?

What are the causes of irregular periods?

Reviewed by Dr. Caroline Fontana
  • Select

  • Fill out a short
    medical form

  • Doctor issues

  • Medication sent
    from pharmacy