Stars who have children in their 40s are giving women false hope about motherhood, doctors warn.
Celebrities who parade "miracle babies" will often have used IVF or donor eggs, they said.
Because they do not make this public their fans fail to realise that fertility declines dramatically after the age of 37.
"If more celebrities were prepared to speak out it would do the world of fertility medicine a lot of good," said Adam Balen of the British Fertility Society.
The issue was thrown into the spotlight by a study showing that at 44 it is almost 20 times harder to get pregnant through IVF than at 39. The rapid speeding up of their biological clock means women in their mid-40s have only a 1.3 per cent chance of the treatment working.
But at the ages of 38 or 39 the success rate is 23.6 per cent. The point at which fertility starts to fall significantly is 38, according to researcher Marta Devesa.
"The prognosis is really futile from 44 and onward," she said. Yet the growth of delayed motherhood means a fifth of British IVF patients are in their 40s.
The study figures come from a Spanish clinic that treated 4,195 patients in 12 years. Some had multiple IVF attempts.
Dr Devesa, of the Hospital Universitari Quiron-Dexeus in Barcelona, said older patients were surprised when told just how low their chances were.
"There is not a lot of knowledge about fertility's decline with age in the general population," she added.
"And it is true that pregnancies in older women and celebrities don't help us because many people don't know that most of the time they have gone for egg donation." Stars who have been open about their pregnancies include actress Nicole Kidman, who was 43 when her second daughter was born via a surrogate mother. The model Caprice also used a surrogate in her early 40s and singer Mariah Carey was 41 when she had IVF twins.
Professor Balen, a consultant in reproductive medicine in Leeds, said: "The key thing is the heartache of infertility that affects older women who haven't realised that it's not so easy to get pregnant just as soon as you wish.
"And while 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 fertility treatment that has been unsuccessful. 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."
Stuart Lavery, director of IVF at Hammersmith hospital in London, said women would be shocked by the figures that were released at the Lisbon conference of the European Society of Human Reproduction and Embryology.
He added: "This should aid conversations with patients about what their realistic hope might be."
However, he disagreed with Dr Devesa's conclusion that women aged 44 and over should use donor eggs, saying many will still want to have a child that is genetically their own.
Professor Charles Kingsland, of the Hewitt Fertility Centre at Liverpool Women's Hospital, said: "Women now make a choice to delay their families.
"I am amazed how women still say 'I am going to get my career, I am going to meet the man of my dreams, I'm going to buy a house and then I'm going to have a family'.
"And I think 'No, you cannot do that'. I'm amazed that even the most well informed of women still don't realise just how much age affects fertility."
- Daily Mail