Schoolgirls are set to get warnings in class about the risks of having children too late amidst fears they could be unable to conceive naturally.

The number of woman giving birth in their late 30s or older has soared in recent years, leading to a huge bill for taxpayer-funded IVF and other fertility treatment.

Now a pilot scheme will educate sixth-form pupils in South London about the health benefits of having children when their bodies are in the optimum stage for childbirth.

However, critics have attacked the lessons for 'putting young women under even more pressure' by making them feel guilty about not becoming a mother as early as possible.

Lessons: Pupils will be told how to boost their fertility in a new pilot scheme (picture posed by models)

Around a dozen schools in the London borough of Merton will now include fertility tips in the relationship lessons attended by pupils aged between 16 and 18.

Girls will be warned that they should have children before their mid-30s if they want to conceive naturally, according to the Sunday Times.

And boys will also be told of the ways they can improve their own fertility, such as cutting down on alcohol and smoking.

Pregnant: Women are encouraged to have children in their 20s or early 30s to avoid conception and health problems (picture posed by model)

The initiative is being funded by the Create Health Foundation, whose founder, hospital consultant Geeta Nargund, fears that schools currently put too much emphasis on contraception while failing to tell pupils how to maximise their chances of starting a family.

'At the moment the focus is on preventing pregnancy but contraception and conception are two sides of the same coin,' Dr Nargund told the paper.

'I've seen so many career women delay having children and then become shocked when they fail to conceive naturally.'

She also called for the lessons to be added to the national curriculum and funded by the Department for Education around the country.

Stephen Alambritis, the leader of Merton Council, added: 'We owe it to our older pupils to give them as much information as possible to make life choices and health choices, including fertility education.'

But some pregnancy experts have criticised the plans, saying that they will make girls feel like they need to get pregnant in their 20s even though many women have children when they are older with no problems.

Clare Murphy, of the British Pregnancy Advice Service, told MailOnline: 'This scheme sounds well-intentioned, but it is quite frankly absurd. Teenagers will not be helped by fertility lessons.

'Women understand that fertility declines with age - they are now subject to relentless warnings about the dangers of leaving it too late, accused of playing reproductive roulette.

'Enough is enough. There is no fertility crisis in this country. Women are simply starting their families later, and doing so for many understandable reasons - the time it takes to establish a career, but equally attain a level of financial security, a home of one's own.

Trend: This graph from the Office for National Statistics shows how the number of older mothers is increasing while under-25s become less likely to have children

Treatment: Many older would-be mothers are reliant on IVF technology to have children

'These issues are likely to be even more pronounced for a younger generation, and lecturing them at school about when they should start trying for a baby is of no help at all.

'The risks of waiting longer to start a family should never be overstated, and where older motherhood may carry slightly increased medical risks, the answer is to ensure our maternity services can cater for women's needs - not put young women under even more pressure about their biological clock.'

The number of over-35s having children has been rising inexorably for the past four decades, while the proportion of mother younger than 25 has fallen equally steeply.

A fifth of children are born to mothers in their late 30s or older, according to the Office for National Statistics, prompting concern among some doctors about the health implications.