Frozen embryo IVF may increase childhood cancer risk

Michael Limmena

Progress Educational Trust

05 September 2022

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[BioNews, London]

Children born from IVF using frozen embryos may have a higher risk of developing childhood cancer according to a new study; however, the overall risk remains low.

Frozen embryo transfer, sometimes called frozen-thawed embryo transfer, is a process in which embryos are frozen before being thawed and implanted for pregnancy. Worldwide, this type of fertility treatment is becoming increasingly more common; and children born from IVF using frozen embryos now exceeds those born using fresh embryos in many countries.

'A higher risk of cancer in children born after frozen-thawed embryo transfer in assisted reproduction, a large study from the Nordic countries found,' said co-author Professor Ulla-Britt Wennerholm from the University of Gothenburg, Sweden. [However] no increase in cancer was found among children born after assisted reproduction techniques overall,' she added.

While elective freeze-all embryo cycles are becoming more common, the long-term medical risks of children being born from frozen embryos remain not well understood. In particular, there are many conflicting studies on the link between children being born using frozen embryos and a higher risk of developing childhood cancer.

Scientists from the University of Gothenburg performed a cohort study using data from almost eight million Scandinavian children, publishing their findings in PLOS Medicine.

The research team analysed the medical records from 7,944,248 million children born in Denmark, Norway, Sweden, and Finland between 1984 and 2015. Of these, 171,744 were born after IVF while the remaining 7,772,474 were not.

Among those born after IVF, 22,630 were born using frozen-thawed embryos. The researchers found that these children were almost two times more likely to develop childhood leukaemia than those born using fresh embryos or natural conception. However, when frozen and fresh embryos were analysed as a single group, children born after IVF did not lead to a higher risk of childhood cancer.

'The large investigation of almost eight million Nordic children is highly impressive.' said CARE Fertility Group's chief scientific officer Dr Alison Campbell, who was not involved in the study.

Despite the study's findings, the researchers emphasised that the results should be interpreted cautiously. Although the study is very large, it is important to note that out of the 22,630 children born after frozen-embryo transfer, only 48 of them later developed cancer. This limits the statistical strength of the study. Moreover, this study cannot determine causation and that the slightly elevated risk, according to the research team, may be due to many different factors wholly unrelated to frozen embryos.

'People who have children born following frozen embryo transfer should not be unduly concerned by the findings because the actual number of children affected by cancer, following frozen embryo transfer, is too small to draw firm conclusions,' noted Dr Campbell.

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