Eggs: quantity and quality

By Razib Khan | December 30, 2011 3:05 am

In my post below on selection for the “better” zygote Michelle observes that “This would be relatively easy for the father, not so much for the mother.” I took her to mean either of two things,

1) Extraction of eggs is a major surgical affair. Extraction of sperm is not.

2) Males generally have many more sperm to contribute than females.

The latter issue made me go look for data on human females, by age. The paper A systematic review of tests predicting ovarian reserve and IVF outcome had what I was looking for. First, let’s review the cumulative distribution of fertility curves for women:


The way I read the figure 50% of women are sterile at 41. 50% begin their fertility drop at 31. Note that a small, but significant, minority of women are already sterile by age 35. People talk about fertility curves, but less weight is given to the fact that the curve varies in terms of its chronology!

Second, let’s look at the number and quality of ovarian follicles over time (they correspond to number of incipient eggs):

This figure is not easy to read. But you can see that at age 20 there are ~100,000 follicles. That number seems to drop by a little less than half by 30, and is at 20,000 by 40. But by this point 25 percent are of “poor quality.”

CATEGORIZED UNDER: Medicine
MORE ABOUT: Fertility
  • Sandgroper

    “Males generally have many more sperm to contribute than females.” True! :)

  • John Emerson

    Sandgroper got there first.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    lol

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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