Children born from frozen embryos more likely to develop cancer

GOTHENBURG, Sweden — Children born from frozen embryos appear to have a higher risk of developing cancer, according to new research. Researchers from the University of Gothenburg say chemicals used in the thawing process could cause genetic changes that trigger tumors.

The findings add to growing concerns about frozen-thawed embryo transfer. The results come from a study of nearly eight million youngsters in Scandinavia.

“A higher risk of cancer in children born after frozen-thawed embryo transfer in assisted reproduction, a large study from the Nordic countries found,” says co-author Professor Ulla-Britt Wennerholm from the University of Gothenburg in a media release.

Results show the most common forms of the disease in these individuals include leukemia and tumors affecting the central nervous system. The work did not find a greater risk of cancer coming from IVF or other types of assisted reproductive technology (ART).

ART allows an embryo to be created from a human egg and sperm in a laboratory. A doctor usually immediately transfers the embryo to the uterus. However, the practice of freezing and later thawing embryos before implantation is increasing worldwide.

Previous research has found children born after frozen-thawed embryo transfer may face higher short-term risks for certain medical issues, but long-term health issues have been less clear.

Fresh embryo transfer still appears safe

The Swedish team analyzed medical data from Denmark, Finland, Norway, and Sweden, tracking 171,744 children born after ART and 7,772,474 conceived naturally. Among the former group, 22,630 were born after frozen-thawed transfer. Statistical analysis showed they were more prone to cancer onset later in life.

However, when researchers combined these children into a single group – frozen and fresh embryo babies – the use of any type of ART did not produce an increased risk of disease. The researchers emphasize that people should interpret their results with caution. Although the study was large, only 48 children born from frozen embryos later developed cancer.

The new findings follow a study of over a million children in Denmark that found frozen embryo babies are two-and-a-half times more likely to develop childhood cancers. Prof. Wennerholm says further research is necessary to confirm a possible link between the procedure and increased risk of cancer and to identify potential biological mechanisms which cause this.

“The individual risk was low, while at a population level it may have an impact due to the huge increase in frozen cycles after assisted reproduction. No increase in cancer was found among children born after assisted reproduction techniques overall,” Ulla-Britt Wennerholm concludes.

The study is published in PLoS Medicine.

South West News Service writer Mark Waghorn contributed to this report.

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