Women who delay starting a family are risking infertility, a leading doctor has warned.

Ideally, they should try for a baby no later than their late 20s or early 30s, said Adam Balen, chairman of the British Fertility Society.

Those who wait longer face the prospect of being left childless and IVF is no guarantee of success, he added.

Professor Balen spoke out after the IVF pioneer Robert Winston claimed it is good to delay having a baby.

Lord Winston said older mothers, who have had time to gain skills and education, as well as build strong relationships, can provide children with a more stable upbringing.

Speaking at the Cheltenham Science Festival, the broadcaster said: ‘Women are leaving childbirth till later and I think it is really a good thing.’ But Professor Balen, a consultant in reproductive medicine in Leeds, said it is the wrong message to give out.

He added that it gives women false hope and, while he did not want to start an argument with Lord Winston, it is critical that they are informed of the dangers of waiting too long.

Professor Balen said age-related declines in fertility mean older women could remain childless, but those who become pregnant have a higher risk of miscarrying or having a baby with Down’s syndrome.

Couples may think they can control their fertility with contraception, then fall pregnant as soon as they start trying, but ‘sadly it doesn’t work like that’, he added.

Even a young couple at peak fertility has only a one in five chance of conceiving in any given month.

If getting pregnant is a problem, referrals, tests and IVF treatment take time and there is no guarantee of a baby at the end, Professor Balen said. Even the best IVF clinics have only a 50 per cent success rate.

He said: ‘When women or couples come to a fertility clinic, they often express surprise that their fertility is already compromised by their mid-30s. ‘I think it’s false reassurance to suggest that you should get on with your career and then only start a family when the time feels right, because for many people the time may feel right when fertility is already low.’

He added: ‘The key thing is balance. We have to ensure that people are informed and they have all the information. And sadly, I don’t think there is enough information provided.

"I think that ideally, if you are thinking about wanting to have a family, you should be thinking towards not delaying beyond your late 20s, early 30s". Professor Balen said society should support women so they do not have to choose between starting a family and having a career.

"I agree that women should be enabled to choose their career path, become established and have a family, but it should be all of these things together – I think that’s the key thing", he added.

His comments echo those made by Geeta Nargund, a leading NHS doctor, last month. She said that if a woman is financially and emotionally stable, she should ideally start trying for a baby before she is 30.

Last night, Professor Nargund, head of reproductive medicine at St George’s Hospital in London, said: ‘Let us not mislead women by telling them to delay having children.

‘We have an obligation to give them scientific facts.’ Lord Winston said he stood by his remarks. He added that Professor Balen is entitled to his opinion, but ‘my own view is that we should be very cautious about offering home-spun advice and we shouldn’t exaggerate the problem’.