(Reuters Health) - When frozen embryos are used during in vitro fertilization (IVF), the resulting children have a slightly higher risk than other kids for certain types of cancer, evidence from Denmark suggests.
Analyzing health records of more than a million Danish children, researchers found that babies conceived through assisted reproduction involving frozen embryo transfer were more than twice as likely to develop childhood cancer, particularly leukemia and neuroblastoma, a type of brain cancer, according to the report in JAMA.
"We did not find increased risks with other types of fertility treatments," said study leader Marie Hargreave of The Danish Cancer Society Research Center, in Cophenhagen.
Hargreave called for more research to validate her group's findings. Moreover, "it is important to stress the fact that the increased risk is very small for the individual as childhood cancer is very rare," she said in an email.
Denmark has one of the highest rates of assisted reproduction technology in the world. In 2018, 9.8per cent of newborns there had been conceived with fertility treatments, the researchers note in their report.
To see whether techniques used in assisted reproduction might elevate cancer risk in children, Hargreave's team turned to national registries of births, deaths and medical records.
The analysis found the incidence of childhood cancer among children born to women with no fertility issues was 17.5 per 100,000. For children born as a result of frozen embryo transfer, the incidence was 44.4 per 100,000, which translated to a 2.43-fold higher risk.
There were no other statistically-meaningful increases in cancer risk for children conceived through any other assisted-reproduction techniques.
Overall there had been 341 childhood cancer cases during the time period studied: January 1, 1996 through December 31, 2012.
The new study has looked at an important question, said Dr. Alan B. Cooperman, director of the division of reproductive endocrinology and infertility at the Mount Sinai Health System in New York City.
But because the study looks only at an association, "it is not clear whether the finding is related to the procedure itself or the patients who needed the procedure," Cooperman said in an email. Beyond that, "any time a rare event is studied in a large retrospective study, the statistical precision to make accurate conclusions is limited."
With that said, "prospective parents can be reassured that in 12.2 million 'person-years' of follow-up, that childhood cancer was diagnosed in less than 0.01per cent of children, regardless of whether or not IVF was used for conception," Cooperman noted.
With frozen embryo transfers becoming more and more common, it will be important to see more studies on this topic, said Dr. Sunita Katari, an assistant professor at the Magee Center for Fertility & Reproductive Endocrinology at the UPMC Magee-Womens Hospital in Pittsburgh, Pennsylvania. "It's something that really needs more investigation and larger studies from different countries," Katari said.
It would also be helpful to have information "on the actual diagnosis of individuals going through fertility treatments in this study," Katari said.
SOURCE: https://bit.ly/2PsQV2w JAMA, online December 10, 2019.