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Although living a healthy life will certainly help if you’re trying to conceive, the age of the mother-to-be is the single most important factor. Women are born with all the eggs they will ever have and as a woman ages, these are released, disappear and deteriorate. A study by the University of St Andrews and Edinburgh University found that by age 30, on average, women had only 12 per cent of their eggs left. By 40, women had only three per cent of their eggs. Fertility also declines in men as they age, but at a slower rate.