Everything you need to know about menstruation and periods

What happens during the four menstrual cycle stages, including how much bleeding is normal, how to track it and what causes period pain.

how the menstrual cycle works
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Confused about the menstrual cycle, ovulation and how periods work? You're not alone. Despite menstruating every month for a sizeable chunk of our lives, many women don't fully understand the process until they decide to start a family. So what exactly is the menstrual cycle and how does ovulation work?

What is menstruation?

The menstrual cycle is regulated by hormones from the brain and ovaries that fluctuate at various stages. A typical menstrual cycle lasts for 28 days, but every woman is different, and it is perfectly normal for your cycle to last anything between 21 and 45 days.

Menstruation – having periods – is part of the female reproductive cycle that starts when girls become sexually mature at the time of puberty. The female internal sex organs consist of two ovaries, the Fallopian tubes, the uterus (womb) and the vagina. During a menstrual period which starts on the first day of her menstrual cycle, a woman bleeds from her uterus (womb) via the vagina, and this lasts anywhere from three to seven days.

But why? Every month, between puberty and the menopause, a woman’s body cycles through a number of changes, including ovulation, in order to prepare for potential pregnancy. If a woman does not become pregnant, then she will have a period.

When does menstruation begin?

Girls typically begin their period between the ages of 10 to 18. The average age is 13.

Women will continue to menstruate until the age of 45 to 55, when menopause begins. A woman will have approximately 500 periods in her lifetime.

The four menstrual cycle stages

The menstrual cycle can be divided into four phases. Narendra Pisal, consultant gynaecologist at London Gynaecology, explains what’s going on during each phase, based on a typical 28-day cycle, and what you can expect to feel both physically and emotionally:

Stage one: The menstrual phase

★ Days 1-5

The first day of your period signals day 1 of your menstrual cycle.

Hormones: All hormones are at a low level during this phase. This means that support to the uterus lining is withdrawn, which leads to your period starting.

What to expect: The thickened lining of your uterus, which is now not needed for pregnancy, is shed as your period. Expect menstrual bleeding and associated cramps. Period blood is composed of the endometrium itself, together with a little fresh blood caused by the breaking of very fine blood vessels within the endometrium as it detaches itself from the inside of the uterus. The amount of blood lost due to the normal monthly period is usually less than 80ml.

What's going on: The lining of the uterus – the endometrium – has been thickened by the action of hormones and made ready to receive a fertilised egg. If the egg is fertilised and the woman becomes pregnant, it will fasten itself onto the endometrium and there won't be any menstrual bleeding. If the egg is not fertilised, however, resultant hormonal changes cause the endometrium to slip away and menstruation begins.

Stage two: The follicular phase

★ Days 1-14

There is overlap with the follicular phase and the menstrual phase.

Hormones: Follicle Stimulating Hormone (FSH), produced by the pituitary gland in the brain, stimulates your ovaries to produce follicles containing immature eggs. Oestrogen levels also start to rise, with the development of an ovarian follicle.

What to expect: This is usually the ‘feel-good’ time of the cycle, with very few emotional symptoms. During this phase, you are more likely to feel happy and energetic.

What's going on: The ovaries contain the eggs with which a woman is born and, during each period, a single egg will usually ripen and mature due to the action of hormones circulating in the bloodstream.

Stage three: Ovulation

★ Day 14

Hormones: On this day, your oestrogen levels will reach a peak, leading to a rise in luteinising hormone (LH), which results in the release of a mature egg, this is called ovulation.

What to expect: Some women may experience ovulation-related pain, also known as mittelschmerz, to one side of their lower abdomen and occasional mid-cycle spotting. This is not serious, but see your doctor if the pain persists, is accompanied by vomiting or fever, or you notice any other unusual symptoms. Some women can get clear discharge during ovulation, and if you are using an ovulation prediction test, it will become positive.

What's going on: Ovulation usually takes place roughly 14 days after the first day of the start of a period; however, the exact timing can vary greatly from woman to woman.

Stage four: The luteal phase

★ Days 14-28

Hormones: Your progesterone levels start rising after ovulation and will continue to stay high if there is a pregnancy. In the absence of pregnancy, your progesterone levels will start falling and your period will start when the hormonal support is withdrawn.

What to expect: Progesterone-related symptoms are common at this time, such as breast tenderness, bloating due to fluid retention and sometimes low mood. Commonly known as premenstrual syndrome (PMS), some women are more likely to experience physical symptoms, while others may experience emotional and psychological symptoms. Whatever symptoms you experience, they tend to be relieved when your period starts (Day 1 of the cycle).

What's going on: When the egg is mature it bursts from the ovary and drifts through the Fallopian tube down into the uterus. The ruptured follicle which released the egg begins to produce high levels of progesterone. If the egg meets a sperm on its journey and the sperm successfully fertilises the egg, then a pregnancy begins. Without fertilisation, progesterone levels fall at the end of the luteal phase returning you to the menstrual phase.

How to track your menstrual cycle

There are a number of benefits associated with being 'cycle-savvy' and tracking your menstrual cycle and hormonal changes, including:

✔️ Being able to predict your next period.

✔️ Being able to predict your ovulation and plan for pregnancy.

✔️ Being more aware of cyclical symptoms, such as pain or PMS, and correlate with your menstrual cycle.

✔️ Monitoring the severity of your periods and period-related symptoms.

✔️ Helping you with natural methods of contraception, for example, if you are using an app to predict when you are most fertile.

What influences menstruation?

Menstruation is a complex process involving many different hormones, the sexual organs and the nervous system. First and foremost, hormones influence menstruation. If they are not in balance, the cycle will similarly be affected. The following factors can influence your menstrual cycle:

• Dysfunctional uterine bleeding

Most period irregularities are due to dysfunctional uterine bleeding (DUB), the medical name for irregular vaginal bleeding with no specific cause. Investigations such as hormone levels and ultrasound of the pelvis are normal in DUB, ask your GP for advice.

• Weight and hormonal imbalance

Weight also influences hormonal balance and menstruation. If a woman is underweight, her hormones will stop working properly and her periods might stop altogether. Recent research has also shown that obesity can throw hormones out of balance and make it harder for women to conceive.

• Stress and hormonal imbalance

Stress also affects the hormones. Many women find that if they are worried about something, it can influence menstruation. In some cases, a woman's period might actually stop if she is very worried about whether she is pregnant.

• Exercise and the menstrual cycle

Regular exercise and keeping fit and healthy can help regulate the menstrual cycle. On the other hand, exercising too much and over-stressing the body can have a negative effect on the hormones to the extent that menstruation may cease.

Problem periods

Problems during menstruation vary from woman to woman. Some women are never bothered by their periods, while others can be badly affected by unpleasant symptoms. If your periods are particularly painful, irregular, or stop altogether, you may be concerned. Problem period symptoms may include:

  • Pains in the abdomen
  • Pain in the vagina
  • Feeling nauseous and generally unwell
  • Diarrhoea
  • Sweating
  • Fatigue

    Painful periods

    Some women experience extremely painful periods known as dysmenorrhoea. There is no single proven theory as to why this occurs, but there are several possible reasons:

    ✔️ Contractions of the uterus similar to those felt in childbirth due to the hormone prostaglandin.

    ✔️ The pain can be caused by the cervix dilating when the blood and the tissue are passed out of the womb.

    ✔️ The pain can be due to earlier infections or inflammations of the uterus, or benign tumours in the uterus.

    ✔️ In some cases, painful periods are hereditary. If a woman has painful periods, her daughters may later be affected in the same way.

    What if your periods stop altogether?

    Periods can stop for a number of reasons. Amenorrhoea is the medical term used to describe a lack of menstrual cycles in women. The most common reasons include the following:

    • Pregnancy.
    • Premature menopause (this can affect women in their early twenties).
    • Weight loss or weight gain.
    • Some forms of medication including the contraceptive pill or injections.
    • Drug abuse.
    • Stress.
    • Hormonal imbalances, such as an under active or overactive thyroid gland or the overproduction of a hormone called prolactin.
    • Polycystic ovaries is a common cause of irregular or absent periods.

      The treatment for amenorrhoea depends upon the diagnosis. If you are uncertain as to why your periods have stopped, seek advice from your doctor. Investigation may involve a blood test to measure the levels of various hormones in your body. However, since what is 'normal' varies greatly with regard to women's hormones, blood tests are not a particularly good measure of what can be considered much more subtle imbalances in a woman's cycle.

      Irregular periods

      Some women experience irregular or infrequent periods, medically known as oligomenorrhoea. This can be either frequently or every few months and is not usually caused by a serious condition.

      The most common cause of infrequent periods is polycystic ovaries. Periods are also often light or infrequent both when a young woman starts having periods, and also when a woman is nearing menopause.

      If you have any concerns about your menstrual cycle, speak to your GP or gynaecologist.

      Last updated: 04-03-2020

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