Certain rare childhood cancers may be more common in children conceived via in vitro fertilization (IVF), a U.S. study suggests, but parents needn't lose sleep over this finding, according to the researchers.
"For the few cancers that seemed associated with IVF the absolute risk was still extremely rare," said lead study author Logan Spector of the University of Minnesota in Minneapolis.
The increased risk of cancer may be due at least in part to advanced maternal age and other health factors that lead women to try IVF in the first place, Spector and colleagues note in JAMA Pediatrics. While the results suggest it may make sense to be vigilant in monitoring IVF children for cancer, they don't mean couples shouldn't try to conceive this way, Spector said by email.
"There was no indication that any specific IVF procedure or treatment was associated with these cancers, so there is not really anything patients or their providers should be doing differently," Spector added. "Overall these results should be reassuring to parents who have used IVF."
Spector's team examined data on 275,686 children conceived with IVF and 2.27 million kids conceived naturally from 2004 to 2013.
They tracked children for an average of about four and a half years, during which time 321 cancers were detected among children conceived by IVF and 2,042 cancers were detected among other kids. That translates to a rate of 0.1 percent among IVF kids and 0.09 percent among naturally-conceived kids.
Put another way, if researchers tracked one million children for a year, they would expect to see one of these rare cancers develop in about 252 children conceived by IVF and about 193 kids conceived naturally.
Specifically, kids conceived using IVF were 28 percent more likely than other children to be diagnosed with embryonal tumors, which develop from embryonic cells that remain in the body after birth. The increased risk of embryonal tumors was driven mostly by a higher rate of liver tumors. Kids conceived by IVF were more than twice as likely to have liver tumors than other children in the study.
Children conceived by IVF were also 41 percent more likely to develop embryonal tumors of the central nervous system, which occur when embryonic cells remain in the brain after birth.
So-called germ cell tumors, or malignancies in the reproductive tissue like the testicles or ovaries, were more than twice as common with IVF.
Overall, children conceived by IVF were 17 percent more likely to develop cancer.
The study wasn't a controlled experiment designed to prove whether or how IVF might directly cause cancer. Researchers also didn't compare outcomes of infertile couples who used IVF to other infertile couples, making it difficult to see how the causes of infertility might influence the potential for rare childhood cancers.
It's possible that cancer can be caused by chromosomal abnormalities, said Dr. Norbert Gleicher, medical director of the Center for Human Reproduction in New York City.
"As eggs age, chromosomal instability increases," Gleicher, who wasn't involved in the study, said by email. "This has been known for decades and is the cause for more chromosomally abnormal pregnancies and miscarriages with advancing age, but this chromosomal instability also leads to more mutations in various genes, many of which may be cancer causing."
Couples considering IVF shouldn't let the slight risk of childhood cancer influence their decisions, Gleicher advised.
"Having a doctor's visit is dangerous because one can be overrun by a car on the way, yet, we go to doctors all the time because the risk is very low and the potential gain by far exceeds the risk," Gleicher said. "The same principle applies here: there are risks in IVF but they are very low (as far as we can see so far) and, therefore, worth taking."