Follicle Stimulating Hormone

The Menstrual Cycle and FSH

Follicle Stimulating Hormone (FSH) is produced by the pituitary gland in the brain. In woman it regulates the growth and development of usually one mature egg-containing follicle by the ovaries per menstrual cycle.

The amount of FSH varies throughout the menstrual cycle and changes over the course of a woman’s childbearing life. When estrogen levels are low this signals the brain to release FSH which stimulates the ovaries to begin ripening around 50-20 follicles each of which contains an immature egg. Rising estrogen levels stimulate the growth of tissues and blood vessels lining the uterus in preparation for receiving a fertilised egg. As estrogen levels increase this cuts down the production of FSH so that normally only one follicle will fully ripen and release a mature egg. The increasing estrogen levels eventually reach a point when they signal to the brain that an egg is ready to be released. In response the pituitary gland in the brain produces a surge of Luteinising Hormone (LH) and FSH which in turn causes the follicle to burst and the mature egg to be released – a process known as ovulation. Once ovulation has occurred levels of FSH decrease until next cycle begins again.

How FSH Influences Fertility

As a woman ages and passes out of the childbearing phase of her reproductive life, her ovaries produce less and less estrogen and hence FSH production increases. Over time these hormonal changes cause menstrual periods to cease completely after which “menopause” is said to have occurred. This change in ovarian function happens slowly, often over a 2 to 10 year period before menopause finally occurs. This early stage is called peri menopause. During this stage FSH is released in greater than normal amounts in order to stimulate the ovaries into producing a mature egg. FSH levels may rise then slowly return to normal again causing irregular or missed periods.


Why Test For FSH?

Urine based FSH tests can provide useful information for woman seeing pregnancy or concerned about their fertility, ovarian health and function. For those experiencing irregular menstrual cycle or finding it difficult to conceive FSH tests can help determine if this is related to elevated FSH levels. As FSH levels should normally below 25mlU/ml, except during mid-cycle, a positive test outside of this time indicates that there has been some disruption in the normal menstrual cycle due to the onset of menopause or some other underlying medical condition.

How To Use FSH Tests

FSH tests are designed to determine the concentration of FSH in urine specimens. FSH testing should be performed at a particular time during your cycle. If you are no longer menstruating the test can be performed at any time. It is important that you carefully follow the directions that come with the tests. For your convenience these can be downloaded and printed our from here - FSH Test Instructions.  As FSH levels can fluctuate a follow up test should be carried out three days following the initial test.