How many eggs is a female human born with?

This “Stump the Teacher” category of posts addresses questions people have asked me in class or questions typed into google which somehow landed people on my blog, to which I did not know the answers or wanted to find out more details. What a fun way for me to learn something new and to share it with you!

While we were discussing the importance of excellent prenatal nutrition (and the potential consequences of poor prenatal nutrition) and the idea that girls are born with all the eggs they will ever have, meaning that pregnant women are in effect also carrying their future grandchildren and should bear that in mind when deciding what to put into their bodies, the question was asked:

How many eggs is a female human baby born with?

I did not know the answer but would have guessed a few thousand – the one we release each month during the reproductive years plus a bunch more for good measure. Thanks to smart phones, we soon learned it’s much much more than that…. in fact, we lose a thousand eggs every month. Wow!

It is commonly believed that, unlike men who produce billions of sperm throughout their lifetime, women are born with a finite number of eggs. At birth, a baby girl has 1 to 2 million immature ‘eggs’ but she loses most of them through a process called ovarian follicle atresia so that by the time she hits puberty, she will only have some 300,000 to 400,000 left. Throughout her reproductive life, from puberty until menopause, about 400 follicles will attain ovulation with an estimated 250,000 follicles lost by atresia at a rate of about 1,000 follicles per month. Of these thousand eggs, only about 20 mature each month and only one of those is released. Once released, it is picked up by the fallopian tube and transported toward the uterus where, if sexual intercourse takes place around this time, the egg and sperm may join and we have fertilization. And then you may end up in my class. :-)

An article titled How Does the Biological Clock Work?, which was written by Dr. S. Silber of the Infertility Center of Saint Louis, puts it this way:

What You Were Born With

“Remember, women are born with all the eggs they are ever going to have, and they don’t make any new eggs during their lifetime. Women are born with approximately two million eggs in their ovaries, but about eleven thousand of them die every month prior to puberty. As a teenager, a woman has only three hundred thousand to four hundred thousand remaining eggs, and from that point on, approximately one thousand eggs are destined to die each month. This phenomenon is completely independent of any hormone production, birth control pills, pregnancies, nutritional supplements, or even health or lifestyle. Nothing stops this inexorable death of approximately one thousand eggs every month regardless of ovulation, ovarian inhibition, or stimulation. Whenever the woman runs out of her supply of eggs, the ovaries cease to make estrogen, and she goes through menopause.”

But even more interesting was the following article I found from February 2012 which references a study first published in 2004, (if you’d like to read the original article in Nature magazine, it’ll cost you $32 here: Germline stem cells and follicular renewal in the postnatal mammalian ovary) one that indicates that women do have ovarian stem cells that may in fact enable them to produce new eggs throughout their reproductive lifetime:

Women Can Make New Eggs After All, Stem-Cell Study Hints

Women may make new eggs throughout their reproductive years—challenging a longstanding tenet that females are born with finite supplies, a new study says. The discovery may also lead to new avenues for improving women’s health and fertility.

A woman has two ovaries, which release eggs during her monthly ovulation.

Previous research had suggested that a woman is born with all the egg cells she will ever have in her lifetime.

But in recent experiments, scientists discovered a new type of stem cell in the ovaries that—when grown in the lab—generates immature egg cells. The same immature cells isolated from adult mouse ovaries can turn into fertile eggs.

It’s a very interesting article! There’s another one here:

Stem Cells In Women’s Ovaries Shown To Make New Eggs, Overturning Fertility ‘Dogma’

For 60 years, doctors have believed women were born with all the eggs they’ll ever have. Now Harvard scientists are challenging that dogma, saying they’ve discovered the ovaries of young women harbor very rare stem cells capable of producing new eggs. [....]

“There’s much more to the story than simply the trickling away of a fixed pool of eggs,” said lead researcher Jonathan Tilly of Harvard’s Massachusetts General Hospital, who has long hunted these cells in a series of controversial studies.

So it seems there’s still a lot more research to be done to fully understand our ovarian mysteries and determine whether we are or are not born with all the eggs we’ll ever have. But ultimately, that doesn’t change the fact that right now, your prenatal nutrition is still super important for you – and your baby, and your baby’s future babies!

I learned something new! Maybe you did too!

All this talk of eggs and ovaries reminded me of a stunning photo that shows the moment an egg emerges from the human ovary, caught by chance during a partial hysterectomy surgery:

You can read more about that here.

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