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.
he 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 else 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 have 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 led by Hospital Universitairo Quiron- Dexeus in Barcelona, involved 4,000 women.
Dr Marta Devesa, lead researcher, said women should be encouraged to start trying for a family at a younger age, or to freeze their eggs by 35, if that was not possible.
She said: "There is a clinically relevant decline from 41/42 - but the prognosis is really futile from 44 and onwards."
"Women should be encouraged to have families earlier but if you can't change society then we should encourage them to freeze their eggs by 35," she said.
Prof Charles Kingsland, from Liverpool Women's Hospital said he many well educated women knew little about their fertility levels.
"I'm amazed at how many women say I'm going to have my career, relationship with the man of my dreams, buy a house then have a family - and I think no you cannot do that," he said.
"Even the most well-informed women are ignorant and still just don't realise how much age affects fertility," Prof Kingsland said.
Prof Stuart Lavery, consultant gynaecologist from Hammersmith Hospital said he thought a lot of people would be "shocked" by just how stark the findings were for women in their early 40s.
He said he hoped the findings would "guide realistic expectations" among older women hoping to start a family.
Separate British statistics which examine the chance of success for each cycle of IVF - but not overall chance of having a baby - show that fertility drops slowly until 37, when a rapid decline starts.
The new research shows what that means for the chance overall of having a baby.
Official figures show one in three females undergoing fertility treatment in the UK are over the age of 38.
Professor Adam Balen, chairman of the British Fertility Society, said: "Whilst you hear lots of good news stories about celebrities who may have given birth at an older age, nobody knows the number of celebrities who may not have been able to have babies, either because of infertility or possibly even having had fertility treatment that has been unsuccessful.
The consultant in reproductive medicine in Leeds said: "There is always a strong possibility that many of these celebrities may well have sought the help of assistance in a fertility clinic and may have conceived either with IVF or donor eggs."