Frozen IVF treatment cycles are up 39 per cent in the UK since 2014, with higher birth rates than fresh.
But researchers now warn that the technique may damage the embryo’s DNA, raising the risk of cancer.
They analysed 1,085,172 children born in Denmark from 1996 to 2012.
Over a period of around 11 years, 2,217 were diagnosed with cancer.
They found that those frozen as an embryo were 2.43 times likelier to develop the disease than those conceived naturally.
The risk of leukaemia was 2.87 times higher, with nervous-system tumours 7.82 times greater.
Patient screamed in agony as docs operated on her while she was conscious
Study leader Dr Marie Hargreave, of the Danish Cancer Society Research Centre, said freezing and thawing embryos may change their DNA.
Figures show 31 per cent of treatment cycles in the UK in 2016 were frozen, with a birth rate of 22 per cent. Some 69 per cent were fresh, with a 21 per cent birth rate.
Dr Alasdair Rankin of cancer charity Bloodwise said: “Childhood cancers are thankfully very rare, so the absolute risk is still low.”