How the Ovaries Produce Eggs

So much of hormone-focused nutrition, especially in the context of fertility and healthy menstrual cycles, is the emphasis on egg quality. “Eat these 5 foods to boost egg quality”, “take this supplement for optimal egg quality”, and so on, and so on. I think a lot of that content is click-bait (because “egg quality” is a bit of a misnomer, but we can talk about that another time) and we miss the most important part - how do eggs actually come to be?

The ovaries put in a lot of work to produce the tissues that may or may not become a human at some point - much more than simply cracking open some cells to make a biological omelette!

Let’s back up the timeline a bit here - what are the ovaries, exactly?

The ovaries are two small, almond-shaped organs located on either side of the uterus, with primary functions to produce eggs (called ova) and hormones including estrogen and progesterone. In most bodies, on a regular schedule, the ovaries will mature and release an egg that can be caught by the fallopian tubes for possible fertilization and implantation.

Egg production itself takes a lot of time! Female embryos have an estimated 6 to 7 million primordial germ cells, or the precursor to ova (this means a pregnant person is carrying their possible grandchildren!). At birth, these germ cells have developed into primary oocytes, and their numbers have dropped to about 1 to 2 million - this decline continues throughout childhood. Each of those primary oocytes are “paused” in their development, in a stage of cell division called prophase I of meiosis. This stage reduces the number of chromosomes by half, so each egg will only carry 23 chromosomes and has the potential to bind with sperm to complete the full set of 46 human chromosomes. This stage continues until puberty!

At puberty, the brain and ovary start communicating with each other via the hypothalamic-pituitary-ovarian (HPO) axis, allowing for hormonal changes to begin that stimulate the ovaries to continue maturing the primary oocytes and developing ovarian follicles. These are fluid-filled sacs that contain immature eggs that progress through a variety of stages as part of maturing and possibly being ovulated. Typically only one follicle matures to a “dominant” state and the other follicles degenerate.

Once that egg is mature, a surge in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) trigger its release from the ovary. After this occurs, the remnants of the follicle become the corpus luteum, a temporary hormone-producing structure that secretes primarily progesterone and some estrogen. Its job is to support early pregnancy should fertilization and implantation occur, until the placenta can take over! If fertilization and implantation don’t occur, the corpus luteum breaks down, hormone levels drop and a period starts.

Egg production is a finely tuned process, with lots of complex interactions that are much more than “on” and “off”. A variety of conditions and concerns can also impact how well eggs are matured, how many are available to be matured and how intact the genetic information is within the egg. When you read about egg quality, think of this as how well the eggs are able to mature and if the genetic material is protected throughout the maturation process! Hint hint - this doesn’t usually warrant tons and tons of fancy or expensive supplements.

And because the hormones involved in egg production are involved in so many other body processes (you need hormones for more than just periods!) ovulation and menstruation are also interconnected with bone health, cardiovascular health, cognitive function, muscle health and even mood. This means big body transitions like puberty, pregnancy and perimenopause can come with additional health and wellness concerns over and above how many eggs you’ve got “left”. Working with an experienced dietitian can help you address these health concerns while also promoting your best hormone and cycle function.

Egg production and ovulation are more than just a day 14 experience, and anyone who tells you it’s that simple is either lying to you or is unaware themselves. Understanding how hormones impact the entirety of the body highlights how complex humans are and how important reproductive health is for our overall well-being!