A study of more than 8 million children in the Nordic countries suggests that children born after the use of a fertility procedure known as frozen-thawed embryo transfer may have a higher risk of cancer than children through other means of reproduction assisted. The results are published in the journal “PLOS Medicine”.
Assisted reproductive technology makes it possible to create an embryo from a human egg cell and a sperm cell in a laboratory. Although it is possible to transfer the embryo immediately to the uterus, it can also be frozen and then thawed before implantation, a practice that is increasing worldwide.
Previous research suggests that children born after this type of technique may have a higher short-term risk of certain medical problems than children after fresh embryo transfer. However, the potential long-term medical risks are less clear.
To improve understanding, Nona Sargisian and her team at the University of Gothenburg, Sweden, analyzed medical data on 7,944,248 children from Denmark, Finland, Norway, and Sweden. A total of 171,744 were born through assisted reproduction, and 7,772,474 were conceived spontaneously. Among the former, 22,630 were born after freeze-thawed transfer.
No increase in cancer found among children born after assisted reproductive techniques overall
Analysis of data from national health registries showed that children born after frozen-thawed embryo transfer had a higher risk of cancer than those born after fresh embryo transfer and those who did not use these techniques.
However, when analyzed as a single group (that is, those born after frozen-thawed embryo transfer and those after fresh embryo transfer), the use of any type of assisted reproduction did not carry an increased risk of cancer.
The researchers stress that their results should be interpreted with caution because, although the study was large, the number of children born after frozen-thawed embryo transfer who subsequently developed cancer was low (48 cases), which could limit the strength analysis statistics.
However, the results may raise concerns about the transfer of frozen and thawed embryos.
For this reason, they say, future research will be necessary to confirm the possible relationship between the procedure and the increased risk of cancer, as well as the biological mechanisms that may underlie said risk.
‘A large study in the Nordic countries found that there is an increased risk of cancer in children born after frozen-thawed embryo transfer in assisted reproduction. The individual risk was low, while at the population level it may have an impact due to the huge increase in freezing cycles after assisted reproduction. We did not find an increase in cancer among children born after assisted reproductive techniques in general”, concludes Ulla-Britt Wennerholm, co-author of the study.