You’re born with 1–2 million potential eggs (in the form of ovarian follicles), but that’s all the eggs you’ll ever have. Up to 1,000 eggs are lost each month. By puberty, your egg count might be 1 million; at 25, maybe 300,000. Then, around 35, the decline starts to get a bit steeper until all eggs have been depleted (menopause).
If you don’t have enough eggs in your ovaries—known as diminished ovarian reserve—you may not ovulate regularly. Most women reach menopause around age 51, but many healthy women will reach menopause in their 40s. Abnormally early menopause, or premature ovarian insufficiency, is when you run out of eggs before you should (before age 40).
Factors affecting egg count:
Age, genetics, medical history, lifestyle
In addition to eggs being lost with age, they can be depleted or destroyed by certain medical treatments, such as chemotherapy or radiation for cancer, or by smoking, which can cause menopause to come up to 4 years earlier. Additionally, genetics comes into play—you’re 6 times more likely to experience early menopause if your mother, sister, or grandmother experienced it. There are also some rare genetic conditions, such as a Fragile X premutation or Turner mosaicism, that are associated with very early menopause.
Tests for egg count:
Measuring the levels of anti-Müllerian hormone, or AMH, in the blood. AMH is produced by the ovarian follicles, so the higher your AMH, the more follicles you have left. Additionally, a focused pelvic ultrasound for antral follicle count (AFC)—more visible follicles are typically indicative of a higher egg count.
Oocyte (egg) donation
Egg quality refers to the genetic health of an egg. The eggs inside your ovaries are “primordial,” or immature eggs. Before you ovulate, they go through another phase of cell division, called meiosis. During this phase, an individual egg can either divide correctly and become healthy (genetically normal, also known as euploid) or divide incorrectly and become unhealthy (genetically abnormal, also known as aneuploid).
Since genetic material—DNA—is like an instruction manual for our cells, any errors in a cell’s DNA can prevent it from doing what it’s supposed to do. Abnormal egg cells typically don’t fertilize or implant in the uterus, but in the rare case they do, they can result in miscarriage or genetic disorders like Down syndrome.
Factors affecting egg quality:
Age, medical history (maybe)
Older eggs are more likely to accumulate errors in their DNA during meiosis, leading to genetically abnormal eggs. That means, as you age, a higher and higher percentage of the eggs inside your ovaries will contain genetic abnormalities. This is why we see infertility, miscarriage, and genetic disorders much more often with women over 35.
It’s theorized that some reproductive illnesses, such as endometriosis, may also affect egg quality—but the relationship isn’t totally clear just yet.
Tests for egg quality:
There’s no test for egg quality, but because egg quality declines naturally and inevitably with age, your age is a good proxy for the percentage of normal eggs you have. Fertilized eggs (embryos) can be genetically tested using a procedure called preimplantation genetic screening/diagnosis (PGS or PGD).
PGS/PGD genetic testing on embryos
Oocyte (egg) donation
Ovulation is the process by which an egg becomes mature within the ovary and is released—normally about once per month. Ovulation is controlled by a delicate balance of multiple hormones produced by the pituitary gland. Some of the primary hormones include follicle-stimulating hormone (FSH), which “activates” a certain number of follicles within the ovary. One of those follicles continues to develop and mature. Luteinizing hormone (LH), also from the pituitary, then increases, telling the mature egg to break free from the follicle and travel down the fallopian tube, where it may be fertilized by sperm.
In order to ovulate, you need to have enough eggs in your ovaries, and you need to have the right balance of hormones—FSH, LH, estrogen, and progesterone—to properly control the process.
Factors affecting ovulation:
Age, hormonal imbalances, lifestyle factors
Because you have fewer eggs as you age, ovulation can become less regular, especially in perimenopause (the 5–10 years leading up to menopause). Ovulation can also be impacted by an imbalance in the hormones that control the process, such as in polycystic ovary syndrome, or by obesity, malnutrition, sleep disruption, stress, or other lifestyle factors that alter hormone levels.
Test for ovulation:
Ovulation predictor kits, blood tests, and ultrasounds.