Egg cells: how many you have and what age does to them

Egg cells are the female reproductive cells, and you receive your entire supply in one go at birth: roughly one to two million. Nothing is ever added. From that moment the supply shrinks every month, whether you're on the pill, pregnant or not thinking about any of it.

That sounds bleak, but in practice the numbers are kinder than they seem. A pregnancy needs exactly one egg a month.

Below you'll see how the supply changes per age, what "egg quality" actually means, and how your own reserve can be estimated.

How many egg cells does a woman have?

At birth roughly one to two million, at your first period an estimated few hundred thousand, and around menopause the supply has nearly run out. Researchers at the University of Edinburgh captured the curve in a model: at 30 about 12 percent of the original endowment remains, at 40 around 3 percent (PMID 20111701).

The decline isn't a leak you can plug, but the pace does differ per woman. That's why two women of 38 can have completely different reserves.

Why do hundreds disappear every month?

Each cycle, a group of follicles, the sacs where eggs mature, enters the race towards ovulation. Usually one wins; the rest of the group shrivels and disappears. Outside that race, resting eggs die off continuously too, a natural process called atresia.

So you "use up" far more than twelve eggs a year, even without ever wanting to be pregnant.

The pill changes little here: it prevents ovulation, not the background loss. You don't save up your reserve with it.

Quantity or quality: which weighs more?

For the chance of a healthy pregnancy, quality usually weighs more than quantity, and quality is mostly tied to age. As eggs get older, the chance of chromosomal abnormalities rises. That lowers the monthly chance of conceiving and raises miscarriage risk, regardless of how many eggs are left.

Take two friends: Lot, 29, with a modest reserve, and Iris, 41, with a generous one. Month by month, Lot probably holds the better cards, because her eggs are younger.

This is exactly why a reserve measurement is never a fertility forecast. In a large study, women with a low reserve value conceived spontaneously just as often as women with a normal one (PMID 29049585).

How do you know if you still have eggs?

As long as you menstruate, you have eggs; your cycle answers that question itself. Roughly how many remain can be estimated with two measurements: the AMH value in your blood and the number of antral follicles on an ultrasound. Both measure the same reservoir by a different route.

The blood route is the more accessible one: an AMH test works on any cycle day, and the result is reviewed by a BIG-registered doctor. What the value does and doesn't mean is covered in our overview of AMH and your egg reserve.

One note I consider mandatory here: don't let a single number scare you. A low value is context for a conversation, not a countdown clock.

Freezing your eggs

If you want to postpone the choice for children, you can have eggs frozen. Clinics often aim for 15 to 20 frozen eggs, because by no means every egg survives thawing, fertilisation and implantation. The younger you freeze, the more each egg is worth.

The reserve measurement plays an honest role here: your AMH helps the clinic estimate how many eggs one retrieval might yield.

If you're weighing now against later, this is one of the few situations where I genuinely think a reserve measurement is sensible. Around 35 the decline accelerates; our article on getting pregnant after 35 digs into that.

If you take one thing from all of this: your egg reserve is a fact, not a grade. If you want to know where you stand because a real choice is on the table, have your AMH measured and take the result to your GP. Meanwhile your ovaries simply keep doing their job, measured or not.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP or your gynaecologist.

References

• Wallace WH, Kelsey TW. Human ovarian reserve from conception to the menopause. PLoS One, 2010. PMID 20111701.
• Steiner AZ, Pritchard D, Stanczyk FZ, et al. Association Between Biomarkers of Ovarian Reserve and Infertility Among Older Women of Reproductive Age. JAMA, 2017. PMID 29049585.
• La Marca A, Spada E, Grisendi V, et al. Normal serum anti-Müllerian hormone levels in the general female population. Eur J Obstet Gynecol Reprod Biol, 2012. PMID 22579227.
• Thuisarts.nl. Wij willen graag zwanger worden.