Women who want a family should conceive or freeze their eggs by 35, doctors have said, after a major study showed fertility falling off a "cliff edge" in subsequent years.
The research shows that women trying to have a baby are 18 times less likely to succeed at the age of 44 as when they are just six years younger.
Senior doctors said findings from the study - the largest and most detailed of its kind - showed the need for women who want children to stop delaying motherhood, or putting careers first.
They said there was a need for "more realistic expectations" among many women, who should either start trying for a family earlier or freeze their eggs.
IVF experts said many women had little idea how low their conception chances were.
Some were given false hope by celebrity mothers having babies in their 40s, with some not admitting they had used donor eggs, they suggested.
The study, presented at the European Society of Human Reproduction's annual conference in Lisbon, shows that at the age of 38 around 24 per cent of women having fertility treatment went on to have a baby.
By the age of 44 the figure was just 1.3 per cent, with a significant decline in live birth rates seen between the ages of 41 and 42.
In all, a woman of 38 trying for a baby was 18 times more likely to succeed than a woman just six years older, the figures show.
The 12-year study involved 4000 women. Dr Marta Devesa, lead researcher, said women should be encouraged to start a family earlier.
"There is a clinically relevant decline from 41/42 - but the prognosis is really futile from 44 and onwards."
Professor Charles Kingsland, from Liverpool Women's Hospital, said many well-educated women knew little about their fertility levels.
"Even the most well-informed women are ignorant and still just don't realise how much age affects fertility."