Children born after ICSI or frozen embryo transfer may have slightly higher risk of childhood cancers

Children conceived through fertility treatment had higher rates of childhood cancer than those conceived naturally, although the absolute risk remains low, new research suggests.

Researchers from the Danish Cancer Institute analysed data from more than one million children born in Denmark between 1996 and 2012, including over 37,000 conceived through fertility treatment. The rate of childhood cancers was higher among the fertility treatment group, particularly those using ICSI or frozen embryo transfers.

'People considering fertility treatment deserve clear and balanced information about potential risks,' said Dr Marie Hargreave from the Danish Cancer Institute, lead author of the study published in JAMA, in a post shared by the Institute on LinkedIn. 'With one in nine children in Denmark now born after fertility treatment, it is particularly important to understand what explains the differences in cancer risk'.

The children in the study were followed for a median of 20 years, during which 3736 cancer cases were recorded.

The researchers compared cancer rates among children conceived through conventional IVF, ICSI and frozen embryo transfer with those conceived without fertility treatment. They also compared outcomes among children born to women with a history of infertility to help distinguish the potential effects of treatment from those of infertility itself.

The overall cancer rate showed a 26 percent relative increase in the fertility treatment cohort, compared to the natural conception group. However, the findings differed by treatment type. Frozen embryo transfer was associated with a 2.18-fold higher cancer rate, while ICSI was associated with a 1.48-fold increase. Standard IVF was not linked to an increased cancer rate.

Despite these relative increases, the absolute cancer rates remained low.

Frozen embryo transfer was associated with higher rates of leukaemia, lymphoma and soft-tissue sarcoma, while ICSI was linked to lymphoma, soft-tissue sarcoma and central nervous system tumours. However, some of these findings were based on small numbers of cases, and further research is needed to determine whether the associations are reliable.

Alastair Sutcliffe, professor of general paediatrics at University College London, who was not involved in the research, commended the quality of the research but cautioned that: 'it is an observational study, and it can show only an association between some fertility treatments and childhood cancer, not that the treatments cause cancer.'

He added: 'The most important point for parents is that the absolute risks are very small. Even in the highest-risk group... well over 99 percent of children conceived this way will not develop cancer in childhood.'

Dr Hargreave and her colleagues plan to extend the research using a Nordic dataset combining registry data from Denmark, Sweden and Norway. The team aims to investigate whether factors such as the method of fertilisation, the use of natural or hormone-prepared cycles for frozen embryo transfer, and embryo-freezing techniques are associated with childhood cancer, while further distinguishing the effects of treatment from those of infertility itself.