How fertility changes with age

What it is

Fertility is the ability to get pregnant and have a baby. For people with ovaries, it changes with age more than most of us were taught. In one study of women aged 18 to 29, only 22% could name the age when drops, the fertile days of the cycle, and the fact that the ovaries don't make new eggs.¹

Fewer eggs

A female fetus has the most eggs she will ever have, about 6 to 7 million, at 20 weeks of pregnancy. By birth about 1 to 2 million are left, about 300,000 to 500,000 at puberty, about 25,000 at age 37 and about 1,000 at 51, the average age of in the US.¹ No new eggs are made. Most are lost to a natural process of breakdown, not to ovulation.¹

Lower quality

matters even more than number. With age, more eggs have the wrong number of chromosomes, which makes a pregnancy less likely to start and more likely to end in miscarriage.¹ There is no test that measures egg quality.¹

The numbers

The chance of getting pregnant in any one month is about 25 to 30% in the 20s and early 30s, and 10% or less by 40.²
About 85% of couples with normal get pregnant within a year of trying.²
The decline is gradual until the early 30s and speeds up after the mid-30s.³
Fertility usually ends 5 to 10 years before .³
Miscarriage, chromosome conditions such as Down syndrome, and pregnancy complications such as gestational diabetes and preeclampsia are more common with age.³

People vary a lot: when the decline starts and how fast it goes differs from person to person.³

Myth: If you're healthy, your fertility will hold up.

It's natural to think fitness and good habits protect fertility, and they do help overall health. But ASRM is clear that a healthy lifestyle doesn't offset the natural age-related decline.³ Smoking, though, does make things worse: it's linked to more infertility and earlier menopause.¹

Myth: IVF can make up for age.

Many people believe this. ACOG says many patients have a false sense of security that IVF can make up for the natural decline, and in one study of graduate students, more than half overestimated IVF success rates.¹ IVF uses the person's own eggs, so it is affected by their age too.

Other things that matter

Beyond age, some things can lower the egg supply faster: smoking, chemotherapy or pelvic radiation, surgery on the ovaries, some genetic conditions, and a family history of early . Thyroid disease, diabetes and endometriosis are strongly linked too.¹

How it compares in boys and men

Men's declines later. In their mid-to-late 40s, changes in sperm can cause fertility problems and raise the chance of genetic and developmental problems in children.³

Recap

Eggs fall from about 1 to 2 million at birth to about 25,000 at 37 and about 1,000 at 51.
Egg quality also declines with age, which makes miscarriage more likely.
The chance of pregnancy each month is about 25 to 30% in the 20s and early 30s, and 10% or less at 40.
Fertility usually ends 5 to 10 years before menopause.
Most people overestimate how likely pregnancy is at every age.

Words to know 4

egg quality	How likely an egg is to have the right number of chromosomes and develop into a healthy pregnancy.
fertility	The ability to get pregnant and have a baby.
menopause	When periods stop for good, confirmed after 12 months without one. Average age 51 in the US.
ovarian reserve	The number of eggs left in the ovaries.