During each menstrual cycle, the body loses approximately 1,000 eggs. This loss occurs through a process called follicular atresia, where the majority of a recruited group of follicles dies off and is reabsorbed by the body. Only one egg typically survives to be released during ovulation.
The mechanism of monthly loss
At the start of every cycle, hormonal signals wake up a cohort of about 15 to 20 follicles from their resting state. These follicles begin to grow, but they compete for dominance. Usually, only one follicle becomes dominant and matures fully to release an egg. The other follicles in that group do not survive; they undergo programmed cell death and are broken down and reabsorbed by the ovarian tissue.
In addition to this cohort loss, there is a constant background loss of primordial follicles through natural apoptosis. When you combine the loss of the competing cohort with this background attrition, the total number of eggs lost per cycle averages around 1,000. This happens continuously, regardless of whether a person is pregnant, using hormonal contraception, or has irregular cycles.
Lifetime egg inventory
To understand why this monthly loss matters, it helps to look at the starting numbers. A female fetus reaches peak egg production around the 20th week of pregnancy, holding about 6 to 7 million eggs. This number drops significantly before birth. By the time a baby is born, the reserve has fallen to roughly 1 to 2 million eggs.
- Fetal peak: 6 to 7 million eggs.
- At birth: 1 to 2 million eggs.
- At puberty: 30,000 to 40,000 eggs.
- At menopause: Fewer than 1,000 eggs.
Over a reproductive lifespan of roughly 35 to 40 years, a person will only ovulate about 400 to 500 eggs. The vast majority of the initial inventory is lost through atresia long before menopause. The body cannot produce new eggs after birth, so this reserve is finite and non-renewable.
Decline rate and age
The rate of egg loss is not constant throughout a person’s life. During the teens and twenties, the total reserve is large, so losing 1,000 eggs a month represents a small percentage of the total. However, after age 35, the decline accelerates. The pool of remaining follicles shrinks more rapidly, and the quality of the eggs also tends to decrease. This drop in quality is linked to an increase in chromosomal abnormalities, which makes conception more difficult and increases the risk of miscarriage.
Measuring ovarian reserve
Doctors use specific tests to estimate how many eggs remain. These tests do not count every single egg but provide a reliable snapshot of the overall ovarian reserve.
- Anti-Müllerian Hormone (AMH): A blood test that measures a hormone produced by the follicles. High AMH levels generally indicate a larger egg reserve. This test is stable throughout the menstrual cycle.
- Antral Follicle Count (AFC): An ultrasound performed early in the cycle (days 2 to 5) that counts the small, visible follicles in the ovaries. This gives a visual estimate of the remaining pool.
These metrics help reproductive specialists assess fertility potential and guide treatment decisions. Understanding that the body loses eggs constantly, even when not actively trying to conceive, highlights the importance of knowing one’s ovarian reserve.