The Menstrual Cycle - periods
The menstrual cycle is a recurring cycle of physical changes that occurs in females of reproductive age. The average cycle length is 28 days, although each woman is slightly different and each individual cycle may also vary slightly.
The menstrual cycle is divided into several phases: the lead up to ovulation, ovulation itself, the phase leading to menstruation and finally menstruation (your period).
Day one of the menstrual cycle is measured as the day on which your period begins. However, to appreciate the hormonal changes leading up to your period, it is useful to understand the physical processes that occur from the lead up to ovulation through to menstruation.
The lead up to Ovulation
During this phase, the womb lining thickens in response to gradually increasing amounts of oestrogen. A rise in hormone levels in the ovary causes the development of one, or possibly two, eggs.
Ovulation
When the egg has nearly matured at about day 12 of the menstrual cycle, the level of oestrogen in the body triggers a surge of hormones which can last for about 48 hours. This matures the egg and causes the release of the egg, which then enters the fallopian tube. This is known as ovulation.
Some women may experience minor pain during ovulation and the sudden hormonal changes can also sometimes cause a light flow or spotting of blood, at mid-cycle.
The lead up to Menstruation
After ovulation, your body produces large amounts of progesterone, which causes the womb lining to change in preparation for the potential implantation of an egg.
When pregnancy occurs
The most fertile period (the time when you are most likely to become pregnant) is from about five days before ovulation, until one to two days afterwards. However, very few women have a menstrual cycle that is exactly 28 days, with ovulation occurring exactly on day 14.
If a sperm cell fertilizes the egg it will continue on through the fallopian tube to reach the womb about three days later, where it will implant into the wall of the womb. However if an egg is not fertilised, it will disintegrate in the fallopian tube
Menstruation
If implantation does not occur, the levels of progesterone and oestrogen will drop sharply, causing the womb to shed its lining. This is known as menstruation and marks the beginning of the next cycle.
It usually takes two weeks from the time of ovulation until the beginning of menstruation, although the process could take anywhere from 10 to 16 days depending on the individual.
Menstruation usually lasts for three to five days, but anywhere from two to seven days is considered normal. The fluid lost during a period menstrual fluid is a mixture of blood and soft tissue from the womb lining. The amount of fluid lost is usually only about 80ml, which is about half a small cup, although it may actually seem like a lot more.
Age of menstruation
A healthy girl or woman will have periods throughout most of her reproductive life (unless using hormonal contraceptives, or pregnant). The average age for a first period is about 12 years old and the monthly menstrual cycle continues until the menopause, which occurs at the average age of 51.1
