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Children born from frozen eggs twice as likely to develop cancer, major study suggests

Sarah Knapton
Women are increasingly encouraged to freeze their eggs early - Alamy 

Children born from frozen eggs using IVF are more than twice as likely to develop cancer, a major study suggests. 

Danish researchers analysed birth records of more than one million babies born in Denmark between 1996 and 2012.

During the time 2217 were diagnosed with cancer, but the study found that those who were born through frozen eggs had a higher risk, increasing from around one in 480 to one in 240.

The researchers from the Danish Cancer Research Centre in Copenhagen, said that previous studies have shown that babies born from frozen eggs have a higher birth weight, proving that cryopreservation is having an impact on growth in the uterus. 

Excessive growth in the womb has been linked to childhood cancer in the past, and some scientists have suggested the freezing process may make epigenetic alterations to DNA, changing how the genetic code operates, and how the baby develops.  

Writing in the Journal of the American Medical Association (Jama), Dr Marie Hargreave, said: “The use of frozen embryo transfer, compared with children born to fertile women, was associated with a small but statistically significant increased risk of childhood cancer.

“It has been suggested that the use of fertility treatment increases the risk of cancer in children, possibly through epigenetic changes brought on by the use of fertility drugs, assisted reproductive therapy, or both.”

Around 20,000 babies are born through IVF each year in Britain and around 6,000 are from frozen eggs. 

However women are increasingly being encouraged to consider freezing their eggs early, as it allows them to preserve their fertility for longer as younger eggs are healthier and more likely to result in successful pregnancy. 

The number of women choosing to freeze their eggs has quadrupled in the last 10 years when only 234 cycles were carried out and the birth rate is slightly higher for frozen eggs. 

Commenting on the research Prof Abha Maheshwari, Consultant in Reproductive Medicine at the University of Aberdeen, said freezing techniques had improved in recent years and urged prospective parents not to panic. 

Modern techniques such as vitrification, or ‘flash freezing’, are now used to avoid the damage caused from slow freezing techniques used in the past.

“There is no reason to panic but what it highlights is that we need more data on frozen embryo transfer and should be cautious in using it for all unless there is a clinical indication such as ovarian hyperstimulation,” said Prof Maheshwari.

“There are pros and cons with frozen transfers, and they have to be taken in consideration with individualised decisions made for each case rather than a blanket policy of freeze all for all, until more data is available.”

Dr Yacoub Khalaf, Honorary Professor at King's College London, said there could be other explanations for the findings.

“During the period of the study, embryos used for transfer used to be mainly the surplus embryos (which are usually of inferior quality) after fresh embryo transfer,” he said. 

“The repercussions of such a study could include putting patients off this option, perhaps prematurely,  as a cause and effect has not been, and may not be easily established."

Experts also said embryo freezing also ‘freezes in time’ the mother’s age at the point at which the embryos were created offering the chance for much later pregnancies.

And charities also urged patients not to be alarmed by the findings. Dr Alasdair Rankin, Director of Research and Policy at the blood cancer charity Bloodwise, added: “It’s important for parents who had this particular form of fertility treatment not to worry unduly about these findings. 

“While a doubling of relative risk sounds scary, childhood cancers are thankfully very rare, so the absolute risk is still low.”