Children that are born from embryos placed in frozen storage are at an increased risk of developing cancer, an alarming new study finds.
Researchers at the University of Gothenburg in Sweden, found that children born from frozen embryos in particular suffered an increased risk of developing leukemia and cancers related to the central nervous system. Interestingly, the same risk was not found for children born via other assisted fertilization means.
Births from frozen embryos are relatively rare and make up a tiny portion of overall babies born using Assisted Reproductive Technology (ART), and as a result there is little large scale population data available for them.
There are over a million embryos currently frozen in the United States, though a vast majority will never be used. Penn Medicine reports that around one million babies were born via in vitro fertilization from 1987 to 2015 - though nearly all were born using a fresh embryo.
A Centers for Disease Control and Prevention report published in 2017 found found that there were around 29,000 frozen embryos that resulted in a live birth in 2015, the most recently available data, in the United States.
Researchers, who published their findings last week in PLOS, gathered data from 7.9 million children across four Scandinavian countries - Denmark, Finland, Norway and Sweden - for the study.
Of that population, 172,000 were born using ART of some kind, and 22,630 came from a frozen embryo.
Researchers found that children that were born after an embryo was unthawed were more likely to develop cancer at a younger age, with leukemia and central nervous system cancers - usually affecting the brain or spinal cord - being the most common.
On average, 2.07 out of every 1,000 children born via spontaneous conception developed cancer.
Children who were born from a fresh embryo - which makes up a majority of IVF pregnancies - were slightly less likely to develop cancer. Researchers found that 1.97 out of every 1,000 developed the disease.
Those born from a frozen embryo were most at risk, with 2.12 of every 1,000 being diagnosed.
Frozen embryo-born children were often suffering their diagnosis earlier in life as well. The study found 30.08 cases for every 100,000 years of life - nearly double the figures from the fresh embryo and spontaneous birth groups.
Overall case levels were low, though, and researchers do not believe this should scare a prospective family away from freezing their embryos.
'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,' Ulla-Britt Wennerholm, a co-author of the study who serves as an OBGYN, said as reported by UPI.
'No increase in cancer was found among children born after assisted reproduction techniques overall.'
Researchers are not sure why children born from frozen embryos could be at most risk, though they do have a few theories.
'The reason for a possible higher risk of cancer in children born after [embryo freezing] is not known,' they wrote.
'Each childhood cancer type has its own risk factor profile, but many childhood cancers are thought to derive from embryonic accidents and originate in utero.
High birth weight has been associated with higher childhood cancer risk, and [changes to the DNA based on environment] have been proposed as a possible explanation.'
The number of women freezing their eggs has rocketed in recent years, as many in the western world have elected to push back building a family in order to pursue career goals.
In 2018, 13,000 women chose to freeze embryos, up from under 500 nearly a decade before in 2009.
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