A female baby is born with roughly 1 to 2 million eggs, already a sharp drop from the peak count reached months earlier in the womb. At about 20 weeks of gestation, a female fetus has around 6 to 7 million eggs. From that point on, the number only goes down. No new eggs are created after birth.
Why the Count Drops Before Birth
Egg production begins early in fetal development. By about the fifth month of pregnancy, the developing ovaries hold their lifetime maximum of 6 to 7 million eggs. But even before birth, a natural process called atresia begins eliminating most of them. Atresia is essentially programmed cell death: the support cells surrounding each immature egg break down, and the egg is reabsorbed by the body. By the time a baby girl is born, roughly two-thirds to three-quarters of those original eggs are already gone.
This isn’t a sign that something went wrong. It’s the normal biological program. In mammalian ovaries, less than 1% of all follicles (the tiny fluid-filled sacs that house eggs) will ever release a mature egg during ovulation. The remaining 99% are lost to atresia over the course of a lifetime.
How the Numbers Change From Birth to Menopause
The decline continues through childhood, though it’s invisible since the eggs sit dormant until puberty. By the time a girl reaches her first period, she typically has somewhere between 300,000 and 400,000 eggs remaining. That sounds like a lot, and it is, but the rate of loss is constant and accelerating.
Each menstrual cycle, the body recruits a batch of follicles to begin maturing. Usually only one wins the race and releases an egg at ovulation. The rest of that batch die off through atresia. Over a reproductive lifetime spanning roughly 30 to 40 years, only about 300 to 400 eggs will ever be ovulated. The vast majority are lost silently in the background, cycle after cycle.
By the late 30s, the pace of loss speeds up noticeably. By the mid-40s to early 50s, the supply drops low enough that the ovaries can no longer sustain regular hormone cycles, and menopause begins. Research from Kaiser Permanente found that women with very low follicle counts (four or fewer visible on ultrasound) were nearly twice as likely to enter menopause within the following seven years compared to women with higher counts.
Egg Quality Matters More Than Quantity
The number of eggs you have is only half the picture. Egg quality, meaning the likelihood that an egg has the correct number of chromosomes, declines steadily with age. A chromosomally normal egg is far more likely to result in a healthy pregnancy, while an abnormal one is more likely to fail to implant, miscarry, or lead to genetic conditions.
A large multicenter study looking at embryos created through IVF illustrates the shift clearly. Among women under 35, about 59% of embryos tested were chromosomally normal. That percentage dropped to 38% for women aged 38 to 40, and fell to just 17% for women over 42. So even if two women have the same number of remaining eggs, the younger woman’s eggs are statistically far more likely to produce a viable pregnancy.
This is why fertility doesn’t simply correlate with egg count. A 25-year-old with a below-average egg reserve can still have excellent fertility because her eggs are more likely to be chromosomally healthy. A 42-year-old with a decent reserve faces steeper odds because a much larger proportion of her remaining eggs carry errors.
How Doctors Estimate Your Remaining Eggs
There’s no way to directly count eggs, since most sit dormant deep in the ovary. Instead, doctors rely on two indirect measures that together give a reasonable picture of what’s called ovarian reserve.
The first is a blood test measuring anti-Müllerian hormone (AMH), a protein produced by the small follicles in your ovaries. Higher levels suggest more remaining eggs. Cleveland Clinic considers AMH between 1.0 and 3.0 ng/mL to be average, under 1.0 ng/mL to be low, and below 0.4 ng/mL to be severely low. As a rough guide, typical lower-end AMH values by age look something like this:
- 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
The second tool is an antral follicle count (AFC), performed via transvaginal ultrasound. A technician counts the small, visible follicles in both ovaries. Each of those follicles contains an egg that could potentially mature. Together, AMH and AFC give a snapshot of quantity, though neither one measures egg quality.
What Affects the Rate of Loss
Genetics plays the biggest role in how quickly your egg supply declines. If your mother or sisters experienced early menopause, you may follow a similar timeline. But several other factors can accelerate the process.
Smoking is one of the most well-documented. Chemicals in cigarette smoke damage the ovaries directly, and research consistently links smoking to earlier menopause. Ovarian surgery, even for benign conditions like cysts or endometriosis, can also reduce the egg supply by removing ovarian tissue. Certain chemotherapy drugs are toxic to eggs and can cause a sharp, sometimes permanent drop in reserve.
On the other hand, nothing has been shown to slow down or reverse the natural rate of egg loss. Hormonal birth control, for example, suppresses ovulation but does not “save” eggs. The background process of atresia continues regardless of whether you’re ovulating or not. The eggs lost each cycle aren’t the ones being ovulated. They’re the ones dying behind the scenes, and no medication or lifestyle change can pause that.