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What is the Menstrual Cycle


The first day of a woman’s bleed (menses) measured to the day before the start of the next bleed.  Typically around 28 days although it is considered normal to have a cycle from 24 to 35 days.


Why do women have a Menstrual Cycle

At birth a baby girl with have the maximum number of eggs in her ovaries, when her body begins the process of maturing into a woman, usually around the age of 12 her first menstrual cycle starts (although this can be as young as 10 or up to 16). 


This can be an exciting time for a young girl, as it is the first sign that she really is a woman and starting her journey to maturity.  Although, she will need information about personal hygiene, sanitary products, support with period pains, hormone changes and of course sex education.


On average a woman has 480 menstrual cycles in her lifetime not accounting for pregnancy and will have her last period at around 50-55.


What actually happens during a menstrual cycle?

Hormones secreted by the hypothalamus, the pituitary gland, and the ovary regulate a woman’s menstrual cycle.


The hypothalamus is located centrally in the brain and communicates with the pituitary gland.   The most important hormone produced by the hypothalamus for reproduction is called gonadotropin releasing hormone or better known as GnRH. GnRH stimulates the pituitary gland to produce follicle stimulating hormone (FSH) causing egg development and increasing oestrogen levels.


Luteinizing hormone (LH), the other reproductive pituitary hormone, is also produced which aids in egg maturation and provides the hormonal trigger to cause ovulation and the release of eggs from its follical and ovary. Ovulation, takes place 28-36 hours after the onset of the LH surge and 10-12 hours after LH reaches its peak. 


The follical that produced the egg now becomes a corpus luteum and is responsible for producing progesterone in order to thicken the lining (endometrium) of the womb (uterus) in preparation for a fertilised egg.  Oestrogen is still produced. This is called the Luteal Phase and lasts around fourteen days (can be 10-16 days).   If no implanting of an fertilised egg (embryo) takes place declining levels of hormones eventually lead to leading to bleeding (menses)  which is the shedding of the lining of the uterus (endometrium).


And the whole cycle starts again … until menopause (see our page on menopause) >>.


Ovulation & the menstrual cycle -
Narrated 3D animation - YouTube
NHS Video on Menstruation
Painful periods (dysmenorrhoea)

Symptoms may vary but can include


  • Heavy bleed (menstrual flow)

  • Cramping or dull ache of the womb (uterus)

  • Lower back ache

  • Leg ache

  • Headache

  • Diarrhoea or constipation

  • Frequent urination

  • Vomiting (not common)


What are causes period pains?

Most cases of period pain occur when the muscle walls of the womb (uterus) contract, this in turn compresses and constricts its blood vessels reducing blood and oxygen supply.  Tissues in the uterus then release chemicals that activate the pain receptors in your body.


This is not the only cause, and it would be wise to speak to the doctor as there can be more serious underlying causes like pelvic inflammatory disease, Endometriosis or Fibroids to name but a few.


How common are they?

Period pains are most comon in young adults and can dissapate with age and after pregnancy.  Although,  according to the NHS website "three quarters of young women and a quarter to a half of adult women experience pain and discomfort during their period. For up to one in five women, this pain is so severe that it stops them from doing their daily activities."


How long will they last?

Generally the pain starts on or a day before your period and lasts one or two days into the flow.  








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