Women are born with about 2 million eggs, and that number only goes down from there. Unlike sperm, which men produce continuously, a female’s entire egg supply is set before birth. No new eggs are created after that point, so understanding how this supply changes over time can help you make sense of fertility at different life stages.
Egg Count From Birth to Menopause
The number of eggs in a woman’s ovaries follows a steep, one-directional decline that starts before she’s even born. During fetal development, a baby girl’s ovaries hold their peak supply, somewhere around 6 to 7 million immature egg cells. By birth, that number has already dropped to roughly 2 million. Most of those early losses happen through a natural process where the body reabsorbs follicles it doesn’t need.
By the time a girl reaches puberty, about 400,000 eggs remain. That sounds like a lot, but only about 400 to 500 of those will ever be released during ovulation across an entire reproductive lifetime. The rest gradually break down and disappear.
Here’s how the numbers roughly look at key ages:
- Birth: ~2 million eggs
- Puberty: ~400,000 eggs
- Age 37: ~25,000 eggs
- Menopause (around age 51): ~1,000 eggs, most no longer viable
Why You Lose So Many Eggs Each Month
If only one egg is released per cycle, you might wonder why the supply drops so fast. The answer is that ovulation accounts for a tiny fraction of egg loss. Each month, a group of follicles (the tiny sacs that house immature eggs) begins developing. One follicle “wins” and releases a mature egg. The rest of that group, sometimes a dozen or more, simply die off. This process is called atresia, and it accounts for approximately 99% of all egg loss over a woman’s lifetime.
Atresia happens at every stage of follicular development and continues whether you’re on hormonal birth control, pregnant, or not ovulating at all. Birth control doesn’t pause or preserve your egg supply. The background loss continues regardless.
How Age Affects Egg Quality, Not Just Quantity
The raw number of eggs matters, but egg quality matters just as much for fertility. As women age, a higher percentage of remaining eggs carry chromosomal abnormalities. This is why fertility declines more steeply after the mid-30s, even though thousands of eggs are still present. At 37, the roughly 25,000 remaining eggs may include a growing proportion that wouldn’t result in a healthy pregnancy.
This is also why miscarriage rates rise with age. At 25, the chance of miscarriage per pregnancy is around 10%. By 40, it’s closer to 30 to 40%, largely because of egg quality. The eggs that remain are older, and their cellular machinery is more prone to errors during division.
How Doctors Estimate Your Egg Reserve
There’s no way to count your eggs directly, but a blood test measuring anti-Müllerian hormone (AMH) gives a reasonable estimate of ovarian reserve. AMH is produced by the small follicles in your ovaries, so higher levels generally indicate a larger remaining pool of eggs.
Typical AMH values fall between 1.0 and 3.0 ng/mL. Levels below 1.0 ng/mL are considered low, and levels at or below 0.4 ng/mL are severely low. To give you a sense of how AMH tracks with age, here are estimates on the lower end of normal for each age:
- Age 25: 3.0 ng/mL
- Age 30: 2.5 ng/mL
- Age 35: 1.5 ng/mL
- Age 40: 1.0 ng/mL
- Age 45: 0.5 ng/mL
AMH tells you something about quantity but not quality. A woman with a normal AMH for her age could still have difficulty conceiving if egg quality has declined. Conversely, a lower AMH doesn’t necessarily mean pregnancy is impossible. It’s one piece of the puzzle, often used alongside ultrasound follicle counts during fertility evaluations.
When Egg Loss Happens Faster Than Normal
Some women experience accelerated egg loss well before the typical timeline. Primary ovarian insufficiency (POI), sometimes called premature ovarian failure, occurs when the ovaries stop functioning normally before age 40. For some women, this begins as early as the teenage years.
POI differs from early menopause in an important way: women with POI may still have occasional periods and can sometimes become pregnant. With premature menopause, periods stop entirely and natural conception is no longer possible. Both conditions involve follicle problems. Either the body runs out of working follicles earlier than expected, or the remaining follicles don’t respond properly to hormonal signals.
Certain factors can increase the risk of a diminished egg reserve at a younger age. These include autoimmune conditions, genetic disorders like Turner syndrome, cancer treatments such as chemotherapy and radiation to the pelvic area, and ovarian surgery. Smoking is also consistently linked to earlier depletion of egg supply and earlier menopause, typically by one to two years.
What This Means for Fertility Planning
The practical takeaway is that fertility doesn’t fall off a cliff at any single age, but the decline is real and accelerates after about 35. At 30, most women still have a large reserve and good egg quality. By 40, both quantity and quality have dropped substantially. The shift between 35 and 40 is the steepest most women will experience during their reproductive years.
If you’re curious about where you stand, AMH testing is a simple blood draw that can be done at any point in your cycle. It won’t tell you whether you can get pregnant right now, but it can flag whether your reserve is lower than expected for your age, which is useful information if you’re considering the timing of pregnancy or egg freezing.