The total number of healthy eggs (oocytes) in your ovaries at any time is called the ovarian reserve. These are all the eggs that could become available for fertilization by sperm cells. Each egg cell lives inside its own follicle. The size of your ovarian reserve will grow smaller as you age, as egg cells die off. You can read more about egg cells and follicles and how they develop here.
This article is pending medical review.
Contributors
Written by Darina Obukhova and Juliëtte Gossens
Reviewed by Sophie Oppelt
Edited by Juliëtte Gossens
If you have (healthy) ovaries, you were born with about 2 million egg cells in them (1). By the time you hit puberty, there are about 400,000 egg cells left (2). Each year, egg cells die off, and they do this in larger numbers when you’ve passed the age of 35 (3). That means the number of eggs you have depends on how old you are. In fact, scientific research shows that age is the most important factor when it comes to the number of follicles you have: 95% of the variation in the number of follicles you have until you’re 25 depends only on age. The remaining 5% of variation is related to lifestyle factors and events in your medical history, such as smoking, your BMI, whether you’ve had children, and stress (4).
In other words, your lifestyle habits and medical history have very little influence on how many eggs you have at a given moment, at least until you’re 25. After that, the effect of those factors is a bit larger, but your age is still what matters most (4).
The size of your ovarian reserve is also related to the onset of menopause. Menopause happens when there are about 1000 follicles left in your ovaries.
But how do you know how many eggs you have left? And what does it matter? We'll explain that in this article.
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Can I measure the size of my ovarian reserve?
It is possible to measure how large your ovarian reserve is with several different tests, but the most widely used are the anti-Müllerian hormone (AMH) test, the basal follicle stimulating hormone (FSH) test, and the antral follicle count (5). None of these tests can tell you exactly how many oocytes (eggs) you have, but they can indicate whether the size of you reserve is normal or not for how old you are (6).
Anti-Müllerian Hormone
AMH is a hormone produced by granulosa cells (the supporting cells) in follicles and is secreted into the blood. Therefore, AMH levels can be measured by a blood test that can be taken throughout the menstrual cycle (the level of AMH doesn’t change much throughout this cycle). The results indicate the approximate number of remaining eggs you have. This test can’t predict how fertile you are, because that depends on multiple factors, not only on how many eggs you have.
Follicle-Stimulating Hormone
FSH is a hormone released by the pituitary gland in the brain. This hormone influences growth of the ovary and the cells within. It also plays a role in managing the menstrual cycle. The FSH level is measured on day 3 of the menstrual cycle through a blood test. High levels are indicative of menopause. High levels can also happen when you’re receiving hormone therapy (for example in preparation for IVF, which you can read more about here). Low levels are seen when you have a low body weight or you’ve had recent rapid weight loss. Low levels can also mean you’re not ovulating, or that you’re pregnant.
Ultrasound Examination
Lastly, your doctor can use vaginal ultrasound to measure how many eggs you have. This means your doctor inserts an ultrasound wand inside your vagina and counts the number of follicles they see on the screen in both your ovaries. These are the so-called antral follicles, which is just a name for the follicles in a certain stage of development. The total count can predict the size of your ovarian reserve. This means your doctor isn’t counting every single egg you have, but the number they can see on screen predicts how many eggs you have in total. Your doctor can relate this number to what’s normal, so they can make a diagnosis or predict how you will respond to fertility treatment, for example. In addition to counting the follicles, your doctor can look at the rest of your ovaries and uterus during the ultrasound to see if they’re healthy.
From all these tests, the antral follicle count (using ultrasound) and the AMH blood test are most reliable (5, 6). However, using ultrasound to measure the ovarian reserve can be tricky. Your healthcare provider may therefore choose to use a blood test instead, or combine different tests.
In some cases, doing an antral follicle count won’t give your doctor the information they need, for example if you’re on hormonal birth control. This can falsely decrease the measured size of your ovarian reserve (6). Depending on what information your doctor is looking for, they might recommend a blood test instead.
Why would I want to measure the size of my ovarian reserve?
There are several reasons why your doctor would advise to get your ovarian reserve measured. For example, if you’re having difficulties getting pregnant, doing these tests can be important to diagnose infertility (6). They can also be helpful to see if you could benefit from assisted reproductive technologies such as IVF. Besides pregnancy, your doctor can use these tests to see if you might have a disorder of your ovaries, such as polycystic ovarian syndrome (PCOS). Lastly, knowing the size of your ovarian reserve can help to predict your risk of menopause within the following few years. That can be useful for family planning, for example.
What if my ovarian reserve is small?
It’s possible that the results of testing show that you have a small ovarian reserve, also called a poor ovarian reserve. This can reduce your chances of successful assisted reproductive technologies (such as IVF), because it makes it harder to remove enough eggs from your ovaries to fertilize in the lab. A poor ovarian reserve doesn’t necessarily mean you will have a harder time to become pregnant naturally, since this only requires a single egg (6).
It’s also possible that a test shows you have a larger ovarian reserve than other people your age. This can increase your risk of ovarian hyperstimulation syndrome (OHSS) if you undergo assisted reproductive technologies such as IVF (6). You can read more about OHSS here.
Can my body make more oocytes?
To make more oocytes, your body would need stem cells. Stem cells are cells that can produce more of a certain type of cell. For example, stem cells in the skin make sure that new skin cells are produced all the time, so that the skin can be repaired and renewed. Because the number of egg cells becomes so much smaller as you get older, it would be interesting to know if there are stem cells that can produce new egg cells. This is an important topic of conversation and research in the scientific reproductive health community. But recent research doesn’t support the existence of oocyte stem cells in human ovaries (3). This means scientists think that the ovaries stop working when you enter menopause. On average, this happens when you’re around 50 years old (7).
The ovarian reserve is a concept that’s mainly useful if you’re having a hard time getting pregnant, or if your doctor suspects something is wrong with your ovaries. It’s not really important to know how large your ovarian reserve is in other circumstances. Nevertheless, it can be very helpful for diagnosis of several disorders, and when you’re considering reproductive technologies such as IVF. Other than that, don’t worry about it!
References
Cox E, Takov V. Embryology, Ovarian Follicle Development. In: StatPearls. Treasure Island (USA); StatPearls Publishing; 2022.
Ruth K, Perry J, Henley W et al. Events in Early Life are Associated with Female Reproductive Ageing: A UK Biobank Study. Scientific Reports. 2016;6:24710. DOI: 10.1038/srep24710
Williams CJ, Erickson GF. Morphology and Physiology of the Ovary. In: Feingold KR, Anawalt B, Boyce A et al (eds.). Endotext. http://www.endotext.org/; 2012.
Wallace WH, Kelsey TW. Human ovarian reserve from conception to the menopause. PLoS One. 2010;5(1):e8772. DOI: 10.1371/journal.pone.0008772
Practice Committee of the American Society for Reproductive Medicine. Testing and interpreting measures of ovarian reserve: a committee opinion. Fertility and Sterility. 2020;114(6):1151-1157. DOI: 10.1016/j.fertnstert.2020.09.134
Coelho Neto MA, Ludwin A, Borrell A, Benacerraf B, Dewailly D, Da Silva Costa F et al. Counting ovarian antral follicles by ultrasound: a practical guide. Ultrasound in Obstetrics & Gynecology. 2017;51(1):10-20. DOI: 10.1002/uog.18945
Wagner M, Yoshihara M, Douagi I, Damdimopoulos A, Panula S, Petropoulos S et al. Single-cell analysis of human ovarian cortex identifies distinct cell populations but no oogonial stem cells. Nature Communicaitions. 2020;11:1147. DOI: 10.1038/s41467-020-14936-3
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