Female eggs begin declining in both number and quality starting around age 30, with the sharpest drop happening after 35. By 45, the vast majority of remaining eggs carry chromosomal abnormalities that make a healthy pregnancy unlikely without medical intervention. But “going bad” isn’t a single event. It’s a gradual process that starts before birth and accelerates at predictable stages throughout life.
How Egg Supply Changes Over Time
You’re born with every egg you’ll ever have, somewhere between 1 million and 2 million. Unlike sperm, which men produce continuously, your egg supply only shrinks from that point forward. By puberty, you’re already down to roughly 300,000 to 500,000. By age 30, about 70,000 to 100,000 remain. By 40, that number drops to around 10,000.
Most of those eggs are never ovulated. Your body naturally reabsorbs them over time through a process called atresia. Of the hundreds of thousands you start with, only about 400 to 500 will ever be released during ovulation across your entire reproductive life. The rest simply dissolve.
Quantity Isn’t the Whole Story
Running low on eggs matters, but the bigger problem with age is what’s happening inside the eggs that remain. As eggs sit in the ovaries for decades, their internal machinery deteriorates. Specifically, the tiny energy-producing structures inside each egg (mitochondria) become less effective at generating the fuel the egg needs during fertilization and early cell division.
When an egg doesn’t have enough energy, the structures responsible for sorting chromosomes during cell division can collapse. This leads to eggs with the wrong number of chromosomes, a condition called aneuploidy. An egg with too many or too few chromosomes typically either fails to fertilize, fails to implant, or results in a miscarriage. In some cases, it leads to genetic conditions like Down syndrome. The proportion of eggs affected by these errors rises steadily with age, which is why both miscarriage rates and chromosomal conditions become more common in pregnancies after 35.
The Key Age Milestones
Fertility starts declining at 30, but the change is subtle at first. Most women in their early 30s won’t notice a difference. The decline picks up speed in the mid-30s and becomes steep after 37 or 38. Here’s how miscarriage risk alone illustrates the pattern:
- Age 35: About a 20% chance of miscarriage (1 in 5 pregnancies)
- Age 40: About a 40% chance of miscarriage (4 in 10)
- Age 45: About an 80% chance of miscarriage (8 in 10)
Those numbers reflect the rising proportion of eggs with chromosomal problems. At 25, the vast majority of your eggs have normal chromosomes. By 40, a much higher share are abnormal. By 45, getting pregnant naturally is unlikely, and even with IVF using your own eggs, live birth rates are extremely low. Data from fertility clinics shows live birth rates per IVF cycle drop to about 10% at age 43, under 4% at 44, and essentially zero at 45 and older when using a woman’s own eggs.
For comparison, women under 35 using IVF have live birth rates approaching 48% per cycle.
Why Blood Tests Can’t Tell You Egg Quality
You may have heard of the AMH test, a blood test that measures a hormone related to your remaining egg supply. It’s useful for estimating how many eggs you have left (your “ovarian reserve”), and fertility clinics use it to predict how well you’ll respond to egg-stimulating medications. But AMH does not measure egg quality.
Research published in Nature found that AMH levels had no role in predicting whether eggs would develop into healthy embryos, particularly in women over 35. A separate study of women aged 30 to 44 who were trying to conceive naturally found no connection between AMH concentration and their ability to get pregnant. In short, a woman with a high AMH level can still have mostly chromosomally abnormal eggs if she’s older, and a woman with a low AMH level can still have healthy eggs if she’s younger. Age remains the single strongest predictor of egg quality, and no blood test can substitute for it.
What Egg Freezing Can and Can’t Do
Egg freezing pauses the aging clock on the eggs you retrieve. If you freeze eggs at 32, they retain the quality of a 32-year-old’s eggs regardless of when you use them. The catch is that freezing works best when done early enough to capture eggs before significant quality decline has set in.
The highest probability of a future live birth from frozen eggs comes from freezing before age 34, where success rates exceed 74%. After that, the odds gradually decrease. Freezing after 40 drops the probability of a live birth to around 26%. This doesn’t mean freezing at 38 is pointless, but the math shifts considerably. The younger you are when eggs are retrieved, the fewer eggs you need to freeze to achieve a reasonable chance of a baby later.
What Actually Determines Your Timeline
While age is the dominant factor, the exact timeline varies from person to person. Some women experience significant fertility decline in their early 30s, while others conceive naturally at 40 without difficulty. Genetics plays a role: if your mother or sisters went through early menopause, your own egg supply may deplete faster than average. Smoking accelerates egg loss by several years. Certain medical treatments, ovarian surgeries, and autoimmune conditions can also reduce your reserve ahead of schedule.
None of these factors change the fundamental biology. Every woman’s eggs accumulate more chromosomal errors over time. The variation is in how quickly the supply runs down and how early the quality shift becomes clinically significant. For most women, the practical window where both egg quantity and quality support straightforward conception runs from the late teens through the early to mid-30s, with a narrowing but still real window extending into the late 30s.