In England, cervical cancer screening starts at 25, but younger women are dying from the disease. In some European countries screening starts as young as 18Débora welcomes your help and feedback in her research. She can be contacted on Twitter @debmir and via email on cancerscreeningproject@gmail.com

Mark Kelly's sister Leanne died from cervical cancer last year, less than five months after she had been diagnosed. She was due to get married a few weeks later. She was only 25.

As a result of my previous posts, Mark got in touch to ask whether his sister would have survived if she had been screened earlier. Cervical screening in England starts at the age of 25.

Although relatively rare, young women do develop cervical cancer, most famously Jade Goody, who died from the disease in 2009 at the age of 27. So on the face of it, screening under-25s would seem sensible.

But when you look at the scientific evidence, things aren't so clearcut. In addition to spotting abnormal changes that will develop into cancer, screening women under 25 also picks up many more benign changes, which will be treated anyway. This treatment can itself lead to health complications – and it costs money.

Screening younger women, while possibly saving Leanne, would not only cause greater harm for many women but would also leave the health service less able to fund treatment for people with other health problems. So cases like Mark's sister pose a huge moral dilemma for health authorities. The answer boils down to a choice between saving a small number of women from cancer or sparing thousands of women from the long-term effects of unnecessary screening and conserving scarce health service resources.

Professor Julietta Patnick, director of the NHS Cancer Screening Programmes, told me that despite being very likely to have cervical abnormalities at a young age, in most women these resolve harmlessly without any need for intervention. Treatment often involves removing the affected tissue for examination, she said, which weakens the cervix and could "lead to difficulties carrying a baby to full term".

A study published in the Lancet that analysed women who went on to become pregnant after treatment for an abnormal smear found there was an increased risk of premature birth and low birth weights.

The considerable costs of caring for premature babies are a factor in this complex equation – but who would choose between caring for a premature child and preventing a case of cancer?

What if Leanne had lived in another country? Would she have been screened earlier – and diagnosed before her cancer reached stage three?

I recently received an invitation from my GP to have my first smear test, because I am now 25. But in Portugal, where I come from, screening often starts earlier. There is actually no common cervical screening policy between countries – not even within the European Union.

The European Guidelines for Quality Assurance in Cervical Cancer Screening were published last year with the support of the International Agency for Research on Cancer (IARC), part of the World Health Organisation. This EU-funded study was carried out by experts from several countries, including the UK, in an effort to tackle disparities.

Screening programmes are either "organised" (like the British system) or "opportunistic" (they depend on a woman or her doctor taking the initiative to do a smear test). The guidelines "discourage" opportunistic screening, because it results in some people being tested more than necessary, while less wealthy groups are not tested at all.

Programmes are also organised either at regional or national levels, and tests can be taken by different experts. But the main controversy highlighted in the study concerns the age at which girls are first invited for screening.

I have created a map based on data from the European Cancer Observatory on the age defined by 25 member states to begin screening.

It seems most countries have decided not to screen women before the age of 25. The age range recommended by the IARC in 2008 was 20-30, but it changed to 25-30 last year.

Interestingly, in Finland and the Netherlands – countries where the programme rollout is complete – screening starts at the highest recommended limit: 30 years old. This might sound quite late, but according to the Health Council of the Netherlands, 30 is the best age to start screening. The Netherlands and Finland have some of the lowest mortality rates for cervical cancer in Europe.

The EU advises governments to concentrate resources on the age range 30 to 60 years, because these smears are "much more effective in detecting a progressive lesion than a smear taken at age 20". Starting screening at 20 doesn't seem to offer any additional benefit.

In Scotland it starts at 20, whereas in England it starts at 25. Yet England has lower incidence and mortality rates for cervical cancer.

Why is there no common policy across the UK? Professor Patnick said each country sets its own criteria for screening: "While Northern Ireland have recently brought their screening policy in line with England and many other countries, Scotland are yet to update their screening programme in line with the IARC published in 2005."

In June 2009, the NHS Advisory Committee on Cervical Screening agreed unanimously that there should be no change in the current policy. So although this will be no comfort for families like Mark's, the science suggests that the line has been drawn in the right place.

Hazel Nunn, senior health information manager at Cancer Research UK, strikes an optimistic note: "In a few years most 25-year-old women will have been vaccinated. This will have implications for the screening programme – the UK may want to consider new screening methods and change how often a woman is screened."

A revolution in cervical cancer prevention is on the horizon. But for now, for women who are under 25 and have not been vaccinated, the best advice is to have a healthy lifestyle and avoid risk factors for cervical cancer such as smoking.

Next week I will look into testing for human papilloma virus (HPV) as a new way to screen for cervical cancer, and discuss the so-called "arrogance of preventive medicine". What would you like to know?

Débora Miranda is a science journalism MA student at City University London and is investigating these questions for her final project. All her source material is posted on her website cancer-screening.net. She can be contacted via email on cancerscreeningproject@gmail.com and on Twitter @debmir