Study shows rapid decline in women's eggs after 30
Progress Educational Trust05 February 2010
The first study to chart the fate of a woman's supply of eggs from conception to the menopause, carried out by researchers of the University of St Andrews and Edinburgh University, UK, shows that the average 30-year-old woman will have just 12 per cent of her original ovarian 'store' of eggs left. The study, published in the journal PLoS ONE, also shows that by the age of 40, only three per cent of the estimated two million eggs a woman is born with are left. The rapid decrease of a woman's reserve of eggs was known before - but the study is the first to trace its entire path, rather than looking at specific age groups.
The study is based on the histological data of 325 women of a variety of ages, from across the UK, Europe and the US, whose reserve of eggs the researchers assessed. This data was fed into a computer programme which produced a graph showing the decrease in the number of eggs over time. The data collected also showed vast differences between the size of different women's 'ovarian reserve', with some women having more than two million remaining eggs and others as few as 35,000. In addition to the percentage of eggs remaining at a given age, the analysis also revealed that, up to the age of 25 years, lifestyle factors like smoking, weight and alcohol consumption have only little effect on the potential number of eggs.
'There are woman waiting for the next promotion or waiting to meet Mr Right,' said researcher Dr Tom Kelsey of St Andrews University, referring to the fact that more and more women are getting pregnant at a later age. He added: 'Women often do not realise how seriously ovarian reserve declines after the age of 35. Every year that goes by you are losing a big proportion of your ovarian reserve'.
In the future the researchers hope that their findings will be able to be used to advise cancer patients on how to preserve their fertility. Also, if it can be calculated which proportion of the egg supply is likely to be killed off by radiotherapy or chemotherapy, it can be calculated when a patient is likely to go through menopause. Finally, predictions on how long a woman will remain fertile could be used to advise women on when to build a family.
However, the used data is cross-sectional, meaning that there is no longitudinal data available. This is due to the absence of a non-invasive test to count the eggs in the individual women. Professor Rob Norman, South Australian fertility expert and director of Adelaide University's Robinson Institute, questioned the accuracy of the method used in the study. Although surprised about the sharp drop-off in the nu
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