Girls as young as nine should be told not to leave it too late in life to start a family, a leading fertility expert has advised.

Adam Balen, chairman of the British Fertility Society (BFS) and professor of reproductive medicine at Leeds University, said children need to be taught about fertility from a young age.

They should learn that they must eat healthily and exercise to ensure their bodies remain in good shape to have babies.

'This is about how to be healthy and how to protect your future, and about getting things right early,' Professor Balen told the European Society of Human Reproduction and Embryology in Helsinki, Finland.

The British Fertility Society has advised girls as young as nine should be told not to leave it too late to start a family so they look after themselves better (posed by models)

'This is something we have been discussing a lot at the BFS. There were worries about diluting the message [that teenage girls should avoid getting pregnant] and we still have to advise about avoiding STIs [sexually transmitted infections] – but we also need to ensure that young people are getting a better understanding of fertility.

'The key things are the need for a healthy diet, a healthy body weight, doing enough exercise and most importantly not smoking.'

Around one in five British couples suffer infertility. Professor Balen said a survey by the BFS this year found four in five people aged between 16 and 24 wrongly believed female fertility does not start to decline until after the age of 35, when fertility is actually in decline from the late 20s. The NHS cut-off for IVF treatment is 39.

He added: 'We need to get the message across early and consistently to get the habits right from the start. I don't think teenage girls are taking nearly enough exercise, for example.

'We need to keep taking the chance to have these conversations. We should be starting this pre-puberty, around the age of nine or ten, when they are mature enough to start understanding these issues.'

Around one in five British couples suffer infertility. Adam Balen, chairman of the British Fertility Society (BFS), said: 'We need to get the message across early and consistently to get the habits right from the start'

Professor Balen said the teaching of issues concerning fertility should be on the curriculum. 'It needs to be embedded in everyday schooling, and to become a routine part of PSHE [personal, social, health and economic education].'

But critics said that nine may be too young for a discussion about the best time for motherhood.

Norman Wells, of the Family Education Trust, said: 'There is doubtless a time and place for communicating the message that female fertility declines with age and that motherhood cannot be put off indefinitely, but the majority of parents will take the view that the time is not prior to puberty and the place is not the primary school classroom.