A woman typically releases one egg per month. That single egg is the result of a much larger process, though. Each cycle, your body recruits roughly 15 to 20 follicles (tiny fluid-filled sacs in the ovaries, each containing an immature egg), but only one follicle “wins” the race, matures fully, and releases its egg during ovulation. The rest break down and are reabsorbed.
One Egg Released, Hundreds Lost
The distinction between eggs released and eggs lost is important. While only one egg ovulates per cycle, your ovaries lose about 1,000 eggs every month to a natural process called atresia, where immature follicles simply die off without ever developing. This happens continuously, whether you’re ovulating or not, and it’s the main reason your egg supply declines over time.
Over a full reproductive lifetime, only about 400 eggs will ever reach ovulation. The vast majority of your original egg supply is lost to this background process rather than to monthly ovulation itself.
How Your Egg Supply Changes With Age
Women are born with all the eggs they’ll ever have. There’s no new production after birth. The numbers drop steadily from day one:
- At birth: approximately 2 million eggs
- At puberty: about 400,000
- At age 37: roughly 25,000
- At menopause (around age 51): about 1,000
That means by the time your first period arrives, you’ve already lost about 80% of your original supply, all before a single egg has ovulated. The decline accelerates after your mid-30s. Between puberty and age 37, you go from 400,000 to 25,000, a drop that picks up speed in the final decade before menopause.
When More Than One Egg Is Released
Sometimes the body releases two or more eggs in a single cycle, a phenomenon called hyperovulation. This is what leads to fraternal twins. About 20% of people who menstruate have the capacity to hyperovulate, though it tends to be sporadic rather than happening every cycle.
Several factors make hyperovulation more likely. Age is one of the biggest: women nearing the ends of their childbearing years, both teenagers and those in their late 30s or 40s, are more prone to it. In teenagers, the hormonal system is still maturing, which can allow the hormone that triggers ovulation to escape its normal feedback loop. In older women, a shrinking egg reserve can cause the body to ramp up that same hormone, sometimes triggering multiple eggs to mature at once.
Genetics play a role too. If fraternal twins run in your family, you may carry a predisposition toward releasing more than one egg. Stopping hormonal birth control can also temporarily trigger hyperovulation as your body readjusts to its natural hormone levels.
Does Birth Control Save Eggs?
Since hormonal birth control suppresses ovulation, it’s natural to wonder whether it preserves your egg supply by giving the ovaries a break. The short answer: not meaningfully. Hormonal contraceptives stop the final step of releasing an egg, but they don’t stop the background loss of about 1,000 eggs per month through atresia. That process runs on its own biological clock regardless of whether you’re ovulating.
What birth control does affect are the markers doctors use to estimate egg supply. Women on combined oral contraceptives show AMH levels (a blood marker for ovarian reserve) about 30% lower than non-users, and their antral follicle counts are similarly suppressed. This can make it look like the pill has reduced your reserve. But these changes reverse quickly. Within three months of stopping the pill, AMH levels bounce back by about 53%, and follicle counts increase by roughly 41%. The suppression is temporary and reflects the medication’s effect on hormone signaling, not actual egg loss.
How Doctors Estimate Your Remaining Eggs
There’s no way to directly count the eggs in your ovaries without removing them. Instead, fertility specialists rely on indirect measures, primarily a blood test for AMH and an ultrasound to count visible follicles.
AMH levels naturally decline with age. General reference ranges put the average between 1.0 and 3.0 ng/mL, with anything under 1.0 considered low. To give a sense of the trajectory: a typical 25-year-old might have an AMH around 3.0 ng/mL, dropping to about 2.5 at 30, 1.5 at 35, 1.0 at 40, and 0.5 at 45. These numbers represent the lower end of normal for each age, so many women will test higher.
AMH tells you something about the size of your remaining egg pool, but it doesn’t tell you about egg quality, which also declines with age and matters just as much for fertility. A woman with a lower AMH may still conceive easily if her egg quality is good, while a higher AMH doesn’t guarantee it.