Fertility after 35: what the science says

A gradual decline that steepens after 35

The probability of conceiving in a given cycle declines gradually with age, with a steeper slope from 35 onwards. This reflects the fall in ovarian reserve — the number of available eggs — and the decline in their quality, which also raises the risk of miscarriage.

In men a decline also exists, but it starts later and is more gradual.

A rapidly growing population

A study published in The Lancet in 2024, based on Global Burden of Disease data, projects an increase of around 50% in the number of women aged 35 to 49 facing difficulty conceiving between 2023 and 2036: from 53.6 million to nearly 80 million worldwide.

This rise is explained first by a demographic shift — the later age at which couples consider a first child — rather than by a sudden deterioration in individual fertility.

The essential nuance

Older age does not mean automatic infertility. Many spontaneous pregnancies occur after 35, and after 40. What age changes is the average time needed and the window of time available.

That is why the threshold for seeking advice is shortened: 6 months of unsuccessful attempts from age 35, instead of 12. Seeking advice earlier does not mean being infertile; it avoids losing time if an assessment is needed.

What can still be acted on

Age cannot be changed, but it adds to other factors that partly can: smoking, weight, sleep, occupational or household exposures. Acting on these does not compensate for age, but it avoids adding avoidable obstacles.