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Periods (The menstrual cycle)
Why do we have them?
Periods, also called menstruation, start once a female reaches puberty, and are a normal part of growing up.
During the menstrual cycle, the hormones oestrogen and progesterone reach levels which cause the ovaries to release an egg. This egg leaves the ovaries and travels down the fallopian tubes to the uterus (womb).
Meanwhile, in preparation for receiving the egg, the uterus starts to develop a thicker lining. If the egg is fertilized in the fallopian tubes by a sperm (after sexual intercourse), it then attaches to the lining of the uterus and pregnancy begins.
If a sperm isn’t present, the egg just passes through into the uterus without being fertilised. Then, since the uterus no longer needs the extra blood and tissue which made up the thick walls, it sheds them through the vagina. This is called menstrual bleeding.
This cycle happens every month until the ovaries stop releasing eggs (usually when a woman is in her 40s or 50s). The time of life when the last period occurs is called a woman’s menopause. A woman will have approximately 500 periods in her lifetime.
When do periods start to happen?
There is no set age for periods to start. Some girls start menstruation when they're 9 or 10; others do not start menstruating until 15. If your period has not started by the time you reach 16 years, it is often nothing to worry about, but you should consult with your doctor.
The length of the cycle also varies. Some last longer than 28 days, and some are shorter. Some women experience regular periods, for others they may be erratic, for example, they may have two periods in one month and miss having one the next month.
The length of time for menstrual bleeding also varies. Some women bleed for only 3 or 4 days, others bleed for a week. The amount of blood shed varies, some women have heavy periods (i.e. they lose a lot of blood), whilst for other women, their periods are lighter. The average amount of blood lost is usually less than 80ml.
How will my periods affect me?
Women may have body and / or mood changes around the time of their period. Menstrual cramps are pretty common during the first few days of your period. As your period approaches, you may also experience premenstrual syndrome (PMS). You may find your emotions amplified during this time. Some women get depressed, irritated, angry, and others cry more than usual, or get cravings for certain foods. PMS is related to the changes in hormones and is perfectly normal, yet can be very distressing. If, however, you start having problems with symptoms like those described above you should talk to your doctor.
What is a normal cycle?
There are different stages to a menstrual cycle, and understanding them will help to understand how the female body functions. You can think of the menstrual cycle as having four stages:
- Menstruation is the stage during which a female has her period. The day bleeding starts is counted as the first day of a given cycle.
- The pre-ovulatory stage is when her body is getting ready for ovulation – that is to release an egg. Higher levels of oestrogen are produced, and in response to oestrogen stimulation, the lining of the uterus thickens. The length of time the pre-ovulatory phase lasts varies from woman to woman and from month to month.
- Ovulation is the mid-cycle stage and is the time of the month when she is most fertile. This is the time she would be most likely to get pregnant (unless she is taking the contraceptive pill). In this phase her ovaries release an egg.
- Postovulatory stage is the final stage, which in effect is the lead-up to menstruation. This phase lasts for about 14 days and concludes the cycle. She will then have her period and the whole cycle begins again.
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