Children born after frozen-thawed embryo transfer (FET) have an increased risk of developing childhood cancer, according to a study published in PLoS Medicine.
Researchers found that, overall, there was no significant difference in the incidence of childhood cancer between children born after assisted reproductive technology (ART) and those born after spontaneous conception.
However, children born after FET had an increased risk of childhood cancer when compared with children born after fresh embryo transfer or children born after spontaneous conception.
“These results should be interpreted cautiously based on the small number of children with cancer, but the findings raise concerns considering the increasing use of FET,” the researchers wrote.
This study included 7,944,248 children born in Denmark, Norway, Sweden, or Finland between 1984 and 2015. Of these children, 171,774 were born after ART. The mean follow-up was 9.9 years for children born after ART and 12.5 years for children born after spontaneous conception.
Cancer diagnosed before age 18 occurred among 329 children in the ART group and 16,183 children in the spontaneous conception group. Within the ART group, 48 children developed cancer after FET.
The incidence rate of cancer diagnosed before age 18 per 100,000 person-years was similar between children born after ART and children born after spontaneous conception — 19.3 and 16.7, respectively (adjusted hazard ratio [aHR], 1.08; 95% CI, 0.96-1.21; P =.18).
However, children born after FET had a significantly higher risk of developing cancer before age 18. The incidence rate (per 100,000 person-years) was 30.1 after FET, 18.8 after fresh embryo transfer (aHR, 1.59; 95% CI, 1.15-2.20; P =.005), and 16.7 after spontaneous conception (aHR, 1.65; 95% CI, 1.24-2.19; P =.001).
When the researchers tried to assess the risk of individual cancers, they found the sample sizes were generally too small to compare FET, fresh embryo transfer, and spontaneous conception. The team was able to analyze the risk of central nervous system cancers, however, and they found no significant differences between the groups.
In addition, the FET group had an increased risk of leukemia. The incidence rate (per 100,000 person-years) was 14.4 after FET, 6.2 after fresh embryo transfer (aHR, 2.25; 95% CI, 1.38-3.68; P =.001), and 4.9 after spontaneous conception (aHR, 2.22; 95% CI, 1.47-3.35; P <.001).
“[W]hile risk of any cancer was not higher in children born after use of ART, we found that children born after FET had a higher risk of childhood cancer than children born after fresh embryo transfer and spontaneous conception,” the researchers concluded.