Britain is facing an infertility timebomb, as couples delay parenthood and damage their chances of having children in later life.

Couples are "sticking their heads in the sand" and one expert urged 30-year-old women to take a "fertility MoT" test to reveal their prospects of bearing children. "Women do not realise the importance of age when it comes to fertility," said Professor Bill Ledger, of Sheffield University. "They think, 'It won't happen to me, I'm 37, I go to the gym twice a week, I don't drink, I don't smoke, I'm fit – everything about me is young'. Well it is, except your ovaries."

He said the solution was for women to take a blood test that could highlight problems in those who wanted children, but had not started trying. It would cost around £100. Ledger said the NHS would be unlikely to pay if the women were healthy, but argued that if it did, it could save money in the long run.

If necessary, women could then opt for a £200-300 ultrasound scan to look for other problems, as well as discussing their medical histories with doctors. Such a "fertility MoT" could act as a reality check for couples who were unaware they were running out of time, said Ledger, who is also a member of the Human Fertilisation and Embryology Authority (HFEA). Testing at 30 would give doctors time to treat any problems.

The call by Ledger – professor of obstetrics and gynaecology at Sheffield – followed a week in which fertility dominated the news, with stories about postcode lotteries for those seeking IVF treatment, and a study revealing that one in eight couples undergoing treatment had their bill subsidised by an average of £5,413 by would-be grandparents.

Experts also claimed that the public's knowledge about fertility was so limited that an education programme should be introduced in secondary and primary schools.

"Sexual health messages focus entirely on avoidance of sex, but this should be coupled with promotion of fertility awareness," said Dr Mark Hamilton, the leading consultant obstetrician and gynaecologist at Aberdeen Maternity Hospital. "We should be teaching everyone, from childhood up, about all the factors linked to fertility potential, and how the huge range of things from lifestyle choices to genetic inheritance can have harmful effects on that potential." Hamilton – a former chairman of the British Fertility Society – said it was crucial to tackle a "widespread misapprehension" about the success rate of fertility treatments. The chances dip sharply with age: from 31% for women aged under 35, to below 5% among women over 41.

However, the average age at which women have their first child has been rising for decades. For married women, it has breached 30, while increasing numbers are waiting until their 40s. However, fertility halves by the age of 35 and declines dramatically after that.

Tony Rutherford, chair of the British Fertility Society, said: "If a woman leaves it late, by which I mean 36, she is taking a gamble. There's a public health duty for us to ensure that men and women are informed about their fertility potential. At the moment, that's not the case."

But Rutherford said it would be risky if women based their decisions on a blood test: "None of the tests give an accurate answer. They are not reliable. You can be fertile at that moment, but you can't tell what you'll be like two years on."

Other critics agreed. Dr Gillian Lockwood, medical director of Midland Fertility Services and vice president of the Royal College of Obstetricians and Gynaecologists' ethics committee, said: "Someone could be falsely reassured that they have time to wait, when they have an underlying problem that will stop them getting pregnant however good their ovarian reserve is."

Ledger argued that it would be about more than a blood test. "Maybe doing the test is less important than making them sit down as a couple and talk it through – the test is just a hook to hang it on."

Around one in five women reaching the end of their fertile life today is childless, according to the Office for National Statistics. This compares with one in 10 women born in the mid-1940s.

Infertility is estimated to affect around one in six or seven UK couples – approximately 3.5 million people – at some point. Although the majority of these will become pregnant naturally given time, around one quarter will not, said Susan Seenan, of Infertility UK.