Ovulation and the menstrual cycle

Many women are unsure about ovulation and what job their hormones do in controlling it. It is estimated that although 90% of women know what ovulation is, there still is a lot of confusion on how this relates to their fertility.

What is ovulation?

Ovulation is the release of a mature egg from the ovary. Ovulation occurs only once in every menstrual cycle, usually around 12 - 16 days before your next period. Most women in the U.K. believe there is a chance of getting pregnant whenever sexual intercourse takes place. This is not the case, the few days surrounding ovulation, (typically 2-5 days) are the only days in the cycle when you could get pregnant.

Can I feel ovulation?

Some women know when they are ovulating because they can feel a slight pain in their lower abdomen. If you feel no pain when you ovulate you can find out when you are ovulating from natural changes in the body. Your vaginal discharge increases and you may have a slight rise in body temperature, you can read more about these changes in our section called ovulation prediction.

What is the menstrual cycle?

The menstrual cycle varies from one woman to another, it first begins when a girl becomes sexually mature at puberty. The majority of women will have a cycle that lasts between 25-35 days, with the average being 28 days, but this can be longer or shorter. The first day of bleeding is counted as the beginning of your cycle (day 1). Your menstrual cycle is then the number of days before your next period starts (the first day of bleeding). Your period can last anything from 3 to 10 days.

What happens during my menstrual cycle?

The menstrual cycle is a complicated process involving many different hormones, women's sex organs and the brain. The activity of a woman's sexual organs, including their development is under the control of a small gland at the base of the brain, called the pituitary gland. Two of the most important hormones of the pituitary gland are Follicle Stimulating Hormone (F.S.H.) and Luteinising Hormone (L.H.).

A woman has 2 ovaries in her reproductive system, each one stores thousands of follicles, within these follicles are the immature eggs. More than one follicle may start to develop at a time, but usually only one reaches maturity each month.

At the start of each menstrual cycle the pituitary gland releases F.S.H. which makes the immature eggs (follicles) grow (this is why F.S.H. gets it name). While the follicle is developing, the cells around the egg produce the female hormone - oestrogen. Each month oestrogen causes the lining of the uterus to grow and prepares the lining of the uterus (womb) to receive the fertilized egg.

Once the follicle has reached a certain size and development, the rising level of oestrogen in the blood, signal to the pituitary gland that the ovary is ready to release the egg. The pituitary gland then sends out a high level of the hormone L.H. (this is commonly known as ‘the L.H. surge’) and this signals the ovary to release the egg (ovulation). The follicle bursts and the egg leaves the ovary and travels through one of the fallopian tubes to the uterus.

The cluster of cells, which formed the follicle, now called a corpus luteum remains in the ovary and starts to produce the female hormone - progesterone.

If a woman has sexual intercourse with a man at this time and his sperm fertilizes the egg, the woman becomes pregnant. The fertilized egg attaches to the uterus and the corpus luteum keeps producing all the progesterone needed, to keep the egg implanted and growing (click here to read more about fertilization). Progesterone also blocks the release of more hormones (L.H. and F.S.H.) from the pituitary gland so that further ovulation does not occur during pregnancy

If after a few days, no egg is implanted the corpus luteum stops producing hormones and gets reabsorbed in the ovary. The levels of progesterone and oestrogen fall and the lining of the uterus starts to break up. The unfertilized egg and the lining of the uterus are released through the vagina as your ‘Period’ (this process is also called menstruation). The cycle then starts all over again.

A summary of the hormones:

Follicle Stimulating Hormone (F.S.H.)

F.S.H. is produced by the pituitary gland. F.S.H. operates with L.H. to encourage the development of the small follicles (like tiny blisters) in the ovaries. F.S.H. also stimulates the production of the ovarian hormone oestrogen. F.S.H. works with L.H. to regulate the activity of the sex organs in men and women. In men F.S.H is necessary for the development of sperm.

Luteinising Hormone (L.H.)

A hormone from the pituitary gland that stimulates ovulation and the development of the corpus luteum. In men L.H. stimulates the cells of the testes, which secrete the male sex hormone testosterone.

Oestrogen

Oestrogen is produced mainly by the ovaries and is largely responsible for the changes which occur in young women around puberty (e.g. breast development and hair growth).

Oestrogen helps stimulate the growth of the egg within the follicle. In America oestrogen is spelt estrogen.

Progesterone

Progesterone is produced mainly by the corpus luteum in the ovary following ovulation. When progesterone is produced it causes a slight increase in body temperature. It is this rise in temperature that is monitored by women using methods of natural family planning, though this is very unreliable.

Progesterone prepares the lining of the uterus to accept a fertilized egg so that the egg can develop. Progesterone also prevents the release of any further eggs until the pregnancy is terminated.

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