Posted by Neharika Sabharwal on January 28, 2010

The decline of a woman's supply of eggs and fertility is well known, but this was the first time experts explored the entire path from conception to the menopause, and the speed at which the eggs faded.

Tom Kelsey, a Senior Research Fellow at the School of Computer Science, who took part in the research at St Andrew University, said, “Women often do not realize 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.

“A lot of people get to their menopause in their mid or late 40s. It is only the average that goes to 50 or 51.”

Data of 325 women evaluated
Researchers from the University of St. Andrews and Edinburgh University collected data on 325 women in a variety of ages from the U.K., U.S. and parts of Europe.

The researchers then assessed their reserve of eggs by feeding the data into a computer to evaluate how the available supply decreased over the passage of time.

The study revealed that an average woman is born with 3,00,000 ovarian reserves which attains peak at around twenty weeks after conception. However, the potential eggs gradually decline until menopause.

Highlights of the report
The report highlighted that though women continue to produce eggs through their 40’s, the egg production wanes in comparison to the alarming speed of the reservoir’s decline.

The researchers found that nearly 95 percent of the women in the 30’s have only an average of 12 percent of their original egg reserves, which diminish to three percent by the age of 40, making conception a difficult prospect.

By the time a woman attains menopause she has only about 1,000 eggs left.

Another aspect highlighted in the study was that the ovarian reserves varied in different women. While some may have 35,000 eggs, there may be others with more than 2 million. Also the speed at which the ovarian reserve declines is different for everyone.

Explaining the decline, the co-author of the study, Dr. Hamish Wallace said, “Our research shows that they are generally over-estimating their fertility prospects. Our model shows that for 95 percent of women, by the age of 30 years, only 12 percent of their maximum ovarian reserve is present, and by the age of 40 years only three percent remains.”

Implications of the study
The new research provides evidence that women who delay pregnancy are at a significant risk of fertility-related problems.

According to experts, the body selects the best eggs from the reserve hence the quality of the eggs also worsens with age which in turn elevates the risk of giving birth to an unhealthy infant.

Another important implication of the study is that the findings create an awareness of the “biological clock ticking” enabling a woman to start a family early or freeze her eggs for conception later.

The research has been published in the Journal Public Library of Science One.

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