Medically reviewed on March 8, 2022 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.
People born with female reproductive organs enter the world with a staggering number of eggs in their ovaries: the number is between 500,000 and 1,000,000.
That said, egg counts—also known as a person’s ovarian reserve—decline over the human lifespan. Fortunately, while egg quantity is a critical marker of fertility, it’s not the only significant factor determining the ability to conceive or carry a successful pregnancy.
In this article, we’ll discuss how many eggs people assigned female at birth have at different stages in their reproductive life cycle and shed some light on other critical factors that impact female fertility (for at-home testing that can help shed light on your ovarian reserve, consider the Everlywell Ovarian Reserve Test).
So how many eggs does a woman have?
Individuals assigned female at birth are at the height of reproductive potential between their late teens and mid to late-20s. In fact, at the beginning of puberty, the ovarian reserve contains approximately 400,000 eggs .
By the time these individuals reach reproductive maturity, however, they begin to lose their egg supply at the highest rate they’ll experience in their lifetime. The process of egg loss is known as follicular atresia—a kind of cell death that disposes of premature eggs to help keep reproductive cycles moving in due course .
From the 20s onward, female fertility patterns generally align with the following trajectory:
- Fertility in the 30s – 95% of individuals assigned female at birth retain around 12% of their original ovarian reserve by the time they turn 30—approximately 120,000 eggs . The American College of Obstetricians and Gynecologists recognizes 32 as the age when fertility starts to markedly diminish, accelerating its decline after age 37 . Thirty-five is medically recognized as the start of advanced maternal age (AMA).
- Fertility in the 40s – A healthy person’s ovarian reserve reaches a “critical low” of 25,000 eggs between their 37th and 38th year . By the time their 40s begin, people with uteruses have a slim chance of getting pregnant without the support of ART (assisted reproductive treatment). Forty-five is the age that most individuals’ ovarian reserves contain 1,000 or fewer follicles .
It also bears mentioning that the body will only cultivate and prepare approximately 1% of the ovarian reserve pool for ovulation in an individual lifetime .
Each month, a small percentage of the ovarian reserve is stimulated through a process of “follicle recruitment,” in which select eggs are prepared for maturity, released, and potentially fertilized by a sperm cell. In one’s 20s, this recruited percentage rests at around 1400 eggs per month. In one’s late 40s, that number declines to approximately 30 eggs per reproductive cycle .
Interpreting these patterns leaves us with two main takeaways about female fertility:
- There’s a sharp decline in female fertility at approximately 35 years old.
- Age is the most significant factor in determining reproductive potential .
Egg quality is another major factor affecting female fertility, and research shows that both egg quantity and quality diminish as you age.
In fact, after age 35, the quality of the eggs puts you at a higher risk of developing what’s known as “aneuploidy”—a chromosomal abnormality that affects around 5% of pregnancies . This type of complication is more likely to result in miscarriage .
There are two types of aneuploidies:
- Trisomy – This refers to the appearance of an extra chromosome (totaling 3) in developing cells. Babies with trisomy are born with congenital disorders, the most common being Down syndrome (trisomy 21).
- Monosomy – Monosomy occurs when only one chromosome is present in developing cells (rather than the normal 2). Few embryos with monosomy are carried through to term. Live births that are carried through usually result in Turner syndrome.
Research suggests that the aneuploidy incidence in individuals older than 35 is a result of a disruption to meiosis, the process of cellular division, and chromosomal replication that occurs after egg-sperm fertilization .
However, medical research has not yet arrived at a consensus to explain why age causes a general decline of egg quality, or why the likelihood of pregnancy complications increases with age .
Though age is the primary determinant for successful pregnancies, it’s certainly not the only factor that influences fertility.
To that end, it is possible to experience a diminished ovarian reserve before the age of 40, just as many people in their 40s can conceive and successfully carry a pregnancy, particularly with the support of ART.
In the sections below, we’ll detail the other factors involved in determining female fertility. We’ll also guide you through some ways to optimize the approach to reproduction beyond the ovarian reserve.
Female fertility is shaped by a number of different factors, including:
- Egg quantity
- Egg quality
- Hormonal health
- Physiological preparedness for pregnancy
Research shows that 95% of ovarian aging is a result of an individual’s age and their genetic inheritance, while 5% may be a result of environmental influences . Even so, understanding an individual’s reproductive capacity requires us to understand the complete picture of how fertility works.
Below, we’ll take a closer look at two other key factors that may influence female fertility: health conditions and lifestyle .
It’s not uncommon for people assigned female at birth to experience challenges to their fertility. One of the most common obstacles is gynecologic disorders that can affect both the hormones and physical structures involved in reproduction.
Some of the most common conditions responsible for infertility include:
- Primary ovarian insufficiency (POI) – POI is a disorder in which the ovary is unable to cultivate its store of eggs for ovulation, resulting in irregular or missed menstrual cycles. While the exact cause is unknown, POI is most likely a genetic condition, but chemotherapy or surgery may also cause it. While primarily a gynecological disorder, POI can also affect cardiovascular, neurological, and bone health due to a lack of estrogen .
- Polycystic ovarian syndrome (PCOS) – PCOS is one of the most common causes of female infertility, affecting up to 10% of reproductive-aged individuals . It’s caused by an overproduction of androgens, a male hormone that prohibits the growth and ovulation of eggs. It can also lead to the growth of ovarian cysts. Although irreversible, you can manage symptoms of PCOS therapeutically and with lifestyle changes.
- Endocrine disorders – Because the brain and reproductive organs are intimately connected, hormonal dysfunction is a common cause of infertility or difficulty getting pregnant. Hypothyroidism, in particular, can compromise ovulation cycles and the balance of sex hormones. Fortunately, individuals with thyroid disorders can recuperate their ability to conceive with proper hormonal treatment .
While some gynecological and hormonal ailments are correctable with medical intervention, others may result in chronic infertility. If you’ve experienced pregnancy loss, arrhythmic periods, or difficulty getting pregnant, consult a healthcare provider to pursue next steps for assessing your fertility profile.
In addition to specific syndromes that can impair female fertility, there is some evidence to suggest that lifestyle and environmental factors can play a significant role in fertility. These factors include:
- Tobacco use, specifically cigarette smoking
- Alcoholism or alcohol abuse
- Stress, depression, or mood disorders
- Obesity or elevated BMI (body mass index) 
- Poor nutrition 
Research on how nutrition may affect fertility is still forthcoming, but there’s a growing body of evidence to suggest that certain diets and nutrients may help to fortify female fertility.
For instance, multiple studies have identified folic acid as a beneficial nutrient for improving fertility outcomes. Meanwhile, research from the Nurses’ Health Study shows that women who combined plant protein, full-fat dairy products, iron-rich foods, and monounsaturated fats had a 66% lower chance of infertility caused by ovulatory dysfunction .
Though our knowledge base is still unfolding, there’s plenty of evidence to suggest that eating a healthy diet, exercising regularly, and managing stress can help reproductive-aged individuals increase their fertility and chances of a successful pregnancy.
If you plan to start a family someday, experts recommend getting ahead of the biological clock and getting acquainted with your procreative potential as early as possible . Ovarian reserve testing, or ORT, is a diagnostic tool that can equip you with the knowledge of your current and future reproductive health by:
- Taking stock of the eggs available in the ovarian reserve
- Gauging one’s proximity to menopause
- Evaluating potential responsiveness to infertility treatment
Egg freezing can be a beneficial option for fertility preservation. Freezing your eggs means creating an egg reserve that can be used later.
Whether you’re actively trying to get pregnant or are looking to prioritize your reproductive health and well-being, ovarian reserve and fertility testing can help you make informed, meaningful choices about present and future health—as well as the health of future loved ones.
Two Everlywell at-home tests are designed specifically to help provide insight into female reproductive health:
- The Ovarian Reserve Test measures follicle-stimulating hormone (FSH) levels on Day 3 of the menstrual cycle to provide insight into ovarian reserve.
- The Women’s Fertility Test measures levels of 5 key reproductive hormones to gauge fertility and potential hormonal imbalances that may interfere with getting pregnant.
What ovarian reserve testing can tell you about fertility
Freezing your eggs: is it right for you?
Can ovarian cysts cause infertility?
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