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updated 7/19/2010 5:28:35 AM ET 2010-07-19T09:28:35

For the first time, a large study suggests a higher rate of childhood cancer among test-tube babies, but researchers say the reason probably has nothing to do with how the infants were conceived.

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More likely, it's related to the genetics of the parents who turned to in vitro fertilization because of infertility, the study's Swedish authors and other experts say. Also, test-tube infants often are born prematurely and have breathing problems at birth — traits linked in other studies with increased cancer risks.

Still, cancer in these children is rare despite any elevated risks.

"It's rather reassuring," said Dr. Bengt Kallen, the study's lead author and a researcher at the University of Lund. The risk "is so small that it can't matter much for the individual parents or parents-to-be."

The study examined Swedish children conceived by IVF, in which eggs are fertilized with sperm in a lab dish and then implanted in the womb. Research on possible health risks including cancer and birth defects in IVF children has had mixed results.

Dr. Tommaso Falcone, the Cleveland Clinic's obstetrics and gynecology chief, said it's uncertain whether similar results would be found in the more racially diverse United States. About 57,000 infants are born after IVF each year in the U.S., or roughly 1 percent of all births.

The results of the new study were published online Monday in Pediatrics. It analyzed more than 2.4 million births in Sweden between 1982 and 2005, including almost 27,000 IVF babies, along with cancer data in children tracked for up to 19 years.

Overall, 53 IVF children developed cancer versus 38 that would be expected in other children of the same age, a 42 percent increased risk. Leukemia and brain cancers were among the most common.

Kallen said possible reasons for the link include unidentified traits in the parents that might be related to infertility and cancer risks.

Absolute risks for cancer in these children are still very low, "far less than 1 percent," Falcone noted.

Dr. Elizabeth Ginsburg, medical director of the IVF program at Harvard's Brigham and Women's Hospital, said patients nonetheless should be counseled about the study results.

Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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