'We saw that the risk of seven of the 10 most common childhood cancers increased slightly, about seven to 10 percent, with every five-year increase in maternal age,' Spector said.

The researchers noted the father's age did not seem to matter once the mother's age was taken into account.

Spector believes more research needs to be done on why the risk for childhood cancer increases with advancing maternal age, said a U-M release.

Some of the possible explanations could be age-related changes in hormonal levels during pregnancy and alterations in DNA markings in eggs that can be transmitted to the offspring.

The results were published in the July issue of Epidemiology.