Now you can benefit from knowing the most relevant information and facts about conception, pregnancy and fertility: 4 Your Info will give you a clearer and deeper understanding of how it all works.

A woman's biological clock

You've probably heard the term: 'A Woman's Biological Clock', but what does it actually mean? A woman will conceive when her partner's sperm successfully fertilises her egg. A man will make sperm at virtually the same rate throughout his life. However, the story is very different for women.

You are born with all the eggs you are ever going to have. You don't make any new eggs during your lifetime; in fact the highest number of eggs you possessed was while you were still in your mother's uterus: a 20-week-old female foetus has about 7 million eggs. By the time you are born, this number has reduced to around 2 million. The fact that your supply of eggs is continuously reducing needn't be cause for concern, however. It is a natural and continuous process, completely independent of birth control pills, pregnancies, nutritional supplements, or even health or lifestyle. By the time you reach puberty and begin menstruation (start your periods) you will have somewhere between 300,000 and 500,000 eggs remaining. During ovulation, in most menstrual cycles, one of these eggs ripens and is released from your ovary in preparation for fertilisation. However, the decline in eggs continues, and from this point onwards, approximately 1,000 of your eggs are destined to die each month. Over the course of a lifetime you will release, from your ovaries, about 500 eggs in their mature form. When the supply of eggs runs out, your ovaries cease to make oestrogen, and you will go through the menopause. Most women stop menstruating around the age of 50: the average age in the developed world is 51.4 years1. From this point onwards you will no longer be able to get pregnant. So our clocks are ticking. However, there is an interesting 'post-script': Harvard scientists have discovered stem cells in human ovaries which, they say, someday in the future, could possibly help infertile women produce new eggs. Maybe we'll be able to stop that biological clock one day.

1. Henderson KD. et al Predictors of Timing of Natural Menopause in the Multi-ethnic Cohort Study. Am J Epidemiology. 2008;167:1287-94