Many of us are pretty in tune with our bodies. For example, you can likely point right away to that tight spot on your right shoulder that knots up when you’re tense.

Yet you might like to know a whole lot more about what’s going on inside your body. Maybe you’re asking, “What’s the story behind my eggs?”

Yes, babies who have ovaries are born with all the egg cells they’re ever going to have. No new egg cells are made during their lifetime.

This has long been accepted as fact.

Yet research in 2004 initially claimed to show new egg stem cells in mice. This theory has been generally refuted by the wider scientific community, though there’s a small group of researchers still pursuing this work.

FYI: Egg terminology

An immature egg is called an oocyte. Oocytes rest in follicles (fluid-filled sacs) in your ovaries until they begin to mature.

The oocyte grows up to be an ootid and develops into an ovum (plural: ova), or mature egg. For clarity, we’ll mainly stick to the name we’re most familiar with — “egg.”

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As a fetus early in development, a baby with ovaries has around 6 million eggs.

The number of these eggs (oocytes, to be precise) is steadily reduced so that when the baby is born, they have between 1 million and 2 million eggs left.

Sources differ slightly on this number, but most cite a figure within the millions.

Good question. The eggs are there, so what’s stopping the menstrual cycle from starting up?

The menstrual cycle is on hold until you reach puberty. Puberty begins when the hypothalamus in your brain starts to produce gonadotropin-releasing hormone (GnRH).

In turn, GnRH stimulates the pituitary gland to produce follicle-stimulating hormone (FSH). FSH begins the process of egg development and causes estrogen levels to rise.

During puberty, menstruation starts about 2 years after the breast bud, or the tissue that develops into a breast, appears. While menstruation begins at an average age of 12 years, it can start as early as 8 years old and will begin in most people by the age of 15.

When you reach puberty, you have between 300,000 and 400,000 eggs. This decrease is caused by the fact that more than 10,000 eggs die each month before puberty.

Once follicles mature, they finally become sensitive to the hormones of your monthly menstrual cycle.

Every month, the body selects a cohort or group of eggs as “contenders” to ovulate. One egg will ultimately become the dominant follicle.

The follicle contains the one egg that’s ovulated that month and represents your one chance to conceive. (Usually, at least. There are exceptions, which in some cases lead to fraternal twins.)

All the other eggs present in that cycle’s group that haven’t been selected as the dominant follicle undergo atresia, which means that they die. This happens every month. You ovulate one egg, and the rest of the growing cohort or group die. This cycle continues until menopause when there are no eggs left.

The number of eggs that die each month decreases after puberty, though.

After starting the menstrual cycle, a person loses about 1,000 immature eggs every month, according to Dr. Sherman Silber, who authored “Beating Your Biological Clock,” a guide for his patients who have trouble with fertility.

Scientists aren’t sure what prompts this to happen, but they know that it’s not influenced by most things we can control. For example, it’s not influenced by:

  • your hormones
  • birth control pills
  • pregnancies
  • nutritional supplements

The data aren’t yet clear on whether health status and food choices affect oocyte quality or quantity.

There are some exceptions. Smoking accelerates egg loss, according to 2018 research. Certain chemotherapies and radiation do too.

When you reach your early 30s, fertility begins to decrease. It declines more rapidly after your mid-30s, according to the American College of Obstetricians and Gynecologists (ACOG). According to 2010 research, by the time you reach 40 years old, if you’re like most of us, you’ll be down to less than 10% of your prebirth egg supply.

Find out what to know about getting pregnant in your 20s, 30s, and 40s.

If you’re in your 40s, there’s no one-size-fits-all answer to how many eggs you have left. What’s more, certain factors, such as smoking, may mean you have fewer than another person of the same age.

Research has shown that the average premenopausal woman over age 40 has less than a 5% chance of getting pregnant per menstrual cycle.

The average age of menopause, when the menstrual cycle stops, is 51 years in the United States. Some will reach menopause earlier, and some will reach it later.

This means that when only 25,000 eggs are left in the ovaries (around age 37, according to 2014 data from ACOG), you’ll have about 15 years until you reach menopause, on average. At menopause, you’ll have fewer than 100 eggs left.

Find out what you should know about having a baby at 40.

We’ve talked a lot about the number of eggs you have. But what about their quality?

The most important factor that determines egg quality is age. As you age, both the quantity and the quality of your eggs decreases.

Just before ovulation each month, your eggs begin to divide. Older eggs are more prone to errors during this division process, making it more likely that they’ll contain abnormal chromosomes, according to ACOG.

As egg quality decreases, the genetic material becomes more damaged and less reparable. So, when the egg and sperm combine to form an embryo, there’s a higher chance of chromosomal abnormalities or genetic irregularities.

This is why the chances of having a baby with Down syndrome or other chromosomal or genetic differences increase as you age. A chromosomal abnormality is the most common cause of a pregnancy ending before term.

When you run out of your supply of viable eggs, your ovaries will cease to make sufficient estrogen, and you’ll go through menopause. Exactly when this happens depends on the number of eggs that you were born with and how quickly you lose your eggs.

Remember that discrepancy between 1 million and 2 million? If you were born with a larger number of eggs, you may be among the people who are able to have biological children naturally into their mid-40s or even late 40s.

On the other hand, there may be people in their 30s who experience a faster rate of egg loss due to certain risk factors. As a result, they may have fertility concerns or may even experience early menopause or ovarian failure.

Learn about having a baby at 50.

If getting pregnant is a goal and has been difficult, the information we’ve discussed about the average number and life cycle of your eggs may help in talking about your concerns with a healthcare professional.

If you have questions or concerns about your ovarian reserve or your egg quality, be sure to speak with a board certified OB-GYN or fertility doctor who can help assess your risk factors and discuss your options.

If you’re concerned about the time limits of your eggs’ life cycle, you may want to consider freezing your eggs, which is also known as oocyte vitrification or elective fertility preservation (EFP).

Although many people consider freezing their eggs because of the time limits mentioned, others may consider it before starting chemotherapy treatments that could affect their fertility.

(Note: Egg freezing before chemo isn’t considered “elective” because it’s medically indicated fertility preservation.)

Considering EFP? According to one source, your chances of having a child with your frozen eggs are better if you freeze before age 35.

It’s also important to remember that that the more eggs you freeze, the better your chances will be of having a baby if you choose to do so or need to use those eggs. Freezing a higher number of higher quality eggs is more likely if you’re younger.

However, reproductive technologies, such as in vitro fertilization (IVF), are allowing people to start or grow their families much later in life.

Though IVF with your own eggs is unlikely to be a viable option if you have difficulty with fertility and are older than your early 40s, according to research from 2015, donor eggs from a younger person can allow people in their 40s and 50s to conceive.

Talk with a doctor early and often about fertility plans and how fertility can change over time. Know that you have options.