Women's Egg Reserves Drop 90 Percent by Age 30


The number of eggs women have in reserve—the potential number of eggs women are born with—drops by about 90 percent by the time women reach age 30. This finding sheds new light on the saying “the clock is ticking” for women who want to conceive.

The new study by researchers at the University of St. Andrews and Edinburgh University is the first to evaluate the egg or ovarian reserve from before birth to menopause around 50 years of age. Although women may continue to produce eggs up through their forties, this egg production pales when compared with the decline. The researchers note that by age 30, about 95 percent of women have on average only 12 percent of their original egg reserves, and by age 40 just three percent.

Just how large the egg reserve is when a female is born varies greatly from person to person. Based on the information gathered from 325 different women in the United Kingdom, United States, and Europe, the study’s authors found that on average females are born with 300,000 potential egg cells. They observed that the number, however, ranged from as high as more than 2 million to as low as 35,000.


Dr. Hamish Wallace, at Edinburgh’s Royal Hospital for Sick Children and one of the study’s authors, noted that their research indicates that women are over-estimating their fertility. The study’s results suggest that women who want to conceive should not wait too long. Because the body selects the best eggs from the reserve, the likelihood is that the quality of the eggs also declines as women get older, which in turn increases the risk of giving birth to an unhealthy infant.

The study also identified an important but curious change in the egg reserve when a female reaches about age 14 years. According to Tom Kelsey, a Senior Research Fellow at the School of Computer Science at St. Andrews and the study’s co-author, at around that age, “the rate of recruitment of immature eggs towards mature eggs drops off and we don’t know why,” thus prompting the decline in the number of mature eggs.

The results of this study may serve as an alert to women who want to conceive, but who also may want to delay pregnancy beyond age 30, that their egg reserves may be 90 percent depleted by that age, seriously affecting their chances of getting pregnant. Dr. Wallace also noted that their findings could help predict which women may experience early menopause and when to freeze eggs from women who have ovarian cancer.

University of St. Andrews news release, Jan. 26, 2010