Children born when parents use a frozen embryo transfer are at a higher risk of childhood cancer compared with those born to fertile women, a new study has shown.
The study, however, pointed out that the risk remained low.
A total of 1.1 million children born in Denmark between January 1996 and December 31, 2012 were part of the study. Of those children, 2,217 were diagnosed with cancer.
Denmark is one of the countries in the world with the highest rates of assisted reproductive technology. In 2018, nearly 10 per cent of all children were born through some form of fertility treatment.
However, it was unclear from the study whether the increased risk was associated with the underlying infertility of the couples, the fertility drugs used or the use of specific assisted reproduction technologies.
According to the study, published in the Journal of the American Medical Association, the children were likely to be born prematurely, with low birth weights and had some birth defects hence the increased health risks.
Freezing is now an essential part of every clinic in vitro fertilisation (IVF) programmes. Studies have proven that results are better when embryos are transferred in later non-stimulated cycles rather than directly following egg collection.
It involves freezing all embryos in an IVF cycle and transferring after thawing one at a time in later non-stimulated cycles. This maximises cumulative live birth rates per IVF attempt while minimising multiple pregnancies, which increases the health risks for both mother and baby.
The frozen embryo transfer itself is the same procedure as an embryo transfer in a fresh cycle. Once the embryo is thawed, a catheter holding the embryo is gently inserted into the cervical channel and the uterine cavity guided by ultrasound.
The catheter is then removed and checked to make sure the embryo has been transferred. After the transfer, you can return to normal with the embryo quite safe within the uterus. Following embryo transfer, a pregnancy test is usually arranged 12 to 14 days later.
When scientists compared the number of children born to fertile parents with those born using some form of assistance, they noticed an elevated risk of childhood cancer in the cases where frozen embryos were used.
Specifically, the rate of childhood cancer was 17.5 per 100,000 for children born to fertile women and 44.4 per 100,000 for children born using frozen embryo transfer. “We previously showed an association between fertility treatment and childhood cancer risk,” Marie Hargreave, senior researcher at the Danish Cancer Society Research Centre in Copenhagen, Denmark, told Healio Primary Care.
The study, done to examine the association between different types of fertility treatments and cancer risk in children, revealed that there was no significant increase in risk associated with the use of other assisted reproductive technology, including IVF, intracytoplasmic sperm injection or hormonal treatment.
“An increasing number of children worldwide are born after the use of fertility treatment, although it remains unclear whether the treatment affects the risk of childhood cancer and whether any associations observed are due to the use of specific drugs, the use of specific procedures, or underlying infertility,” stated the study.
After 11.3 years, the incidence rate of childhood cancer was 17.5 per 100,000 for children born to fertile women and 44.4 per 100,000 for children born after the use of frozen embryo transfer.
Compared with children born to fertile women, the use of frozen embryo transfer was associated with an elevated risk of childhood cancer, including increased risk of leukaemia and sympathetic nervous system tumours.
There were no statistically significant associations with the use of other types of fertility treatment examined.
However, according to Dr Aggrey Akula, who was not part of the study, the research may require further explanation.
He said the study started in 1996, but since then there have been a lot of changes in technology and protocols in the laboratory which could have an impact if the study was to run again on more recent data.
“More questions need to be answered first,” he said, adding that the study was centred on retrospective data, so researchers were not able to ask why there might be an elevated cancer risk with this procedure.
He added: “Parents shouldn’t worry.”