Dec. 10 (UPI) -- A commonly used method for treating infertility in women has been linked with a "small, but statistically significant" increase in cancer risk among children born via the approach.
In a study published Tuesday in the Journal of the American Medical Association, researchers report that children born following frozen embryo transfer in Denmark were nearly three times more likely to be diagnosed with some form of cancer than those born to women who didn't use fertility treatment.
Although the overall risk for cancer is quite small -- an incidence rate of 17.5 cases per 100,000 children born to women not using fertility therapy versus 44.4 cases per 100,000 children born following frozen embryo transfer -- the authors believe their results indicate the issue is worthy of further exploration.
"More large-scaled high quality studies have to be conducted to confirm our findings," study co-author Marie Hargreave, Senior Researcher, Danish Cancer Society Research Center, told UPI. "Even if our findings should be true, it is important to stress the fact that the increased risk is very small for the individual as childhood cancer is very rare."
Hargreave and her team reviewed data on more than 1 million children born in Denmark between 1996 and 2012, and tracked their health outcomes for more than a decade. Of these, 2,217 children were diagnosed with cancer.
Among the mothers who used fertility treatments, 256,381 were administered fertility drugs -- clomiphene, gonadotropins, gonadotropin-releasing hormone analogs, human chorionic gonadotropin, progesterone and estrogen -- while 36,221 opted for "assisted reproductive technology, including in-vitro fertilization, intracytoplasmic sperm injection and frozen embryo transfer. The authors compared rates of childhood cancer for each of these approaches with cancer rates in children born to fertile women.
In all, there were 14 cases of cancer among 3,356 children born following frozen embryo transfer, including five cases of leukemia, compared to 159 cancer diagnoses among the 910,291 children born to women who did not use fertility treatments.
Overall, just 0.4 percent of children born following frozen embryo transfer were diagnosed with cancer, compared to just 0.01 percent of those born to mothers who did not use fertility treatments.
The authors reported they observed no similar increases in cancer risk with the other types of fertility treatments studied.
The Danish study is not the first to observe an association between fertility treatment and childhood cancer risk, according to Hargreave.
A study in the United States, published in April in JAMA Pediatrics, identified a small increase in childhood cancer risk associated with the use of in-vitro fertilization, but had a shorter follow-up time -- less than five years -- and "was limited by incomplete information on maternal fertility treatment [because] only 83 percent of the clinics were included," noted Hargreave.
She added, "In comparison, our study is based on nationwide registries mandatory by law, which means that we had virtually complete information on all births in Denmark, maternal fertility treatments, childhood cancer, migration, death and parental linkage."