The menstrual cycle - understanding your cycle can help you conceive sooner.

UNDERSTANDING THE MENSTRUAL CYCLE

The menstrual cycle varies from one woman to another. Almost 90% of women have cycles that last 25-35 days and for a given woman each cycle will usually last the same number of days. For most women the regular cycle length is around 28 days, but some women have irregular cycles and this can be an indicator of fertility problems.

The menstrual cycle length is calculated from the first day of the menstrual period - the day that you start bleeding is therefore DAY ONE. You continue counting until your LAST DAY which is the day before your next bleed starts.

This figure shows you the parts of the female reproductive system which have to work together properly for you to be fertile.

The ovaries are where the eggs develop and are released into the fallopian tube for fertilisation to take place.

The released egg has to be fertilised by your partner's sperm in order to make you pregnant. If the egg is not fertilised after ovulation the menstrual cycle will come to an end in around 14 days and you will start bleeding (menstruating) again.

What happens during each menstrual cycle? A woman has two ovaries and each one has stored inside something like 250,000 to 400,000 immature eggs (follicles). Normally, just one of the eggs grows during each menstrual cycle and when it is fully grown and matured it is released into the fallopian tube - this release process is called 'ovulation' and is essential if a woman is to have a chance of becoming pregnant.

The menstrual cycle lasts anything between 21 and 40 days, but for most women it is around 28 days.This natural process will continue each month until you reach the menopause (usually between age 45 and 55).

How is the menstrual cycle controlled? The menstrual cycle is controlled in a complex way by a variety of hormones, but the most important ones are mentioned below. At the start of each menstrual cycle a gland in the brain releases a hormone called Follicle Stimulating Hormone (FSH) into the bloodstream which makes the immature eggs (follicles) grow in the ovaries. One of the follicles grows faster than the others, becomes dominant, and starts to produce hormones called oestrogens which are released into the bloodstream. The oestrogen hormones act with the FSH to help the egg grow more and also signal the womb lining to thicken in readiness to receive the fertilised egg. This thickening process prepares the womb lining rather like a nest for the egg. The oestrogen hormones also make the women produce more vaginal mucus to help the sperm live as long as possible after intercourse.

Hormone Levels Controlling the Menstrual Cycle

Once the egg has fully matured another hormone is released from the brain called Luteinising Hormone (LH). This hormone is released in large amounts and triggers the release of the mature egg into the fallopian tube. If healthy sperm are present in the fallopian tube there is a good chance that the egg will be fertilised.

A fertilised egg takes a few days to travel down the fallopian tube, reach the womb and implant itself in the lining of the womb. As the fertilised egg divides and grows it produces the hormone human Chorionic Gonadotrophin (hCG) and it is this hormone that pregnancy tests are designed to detect. This hormone maintains the lining of the womb so that menstruation does not start, thus allowing the new embryo to keep growing.

If the released egg is not fertilised then it is expelled around day 28 of the cycle along with the lining of the womb and another cycle begins.

Understanding the menstrual cycle is an essential start for women wanting to understand more about their fertility and make the best use of our home fertility tests.