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MONDAY, July 19 (HealthDay News) -- Children conceived using in vitro fertilization have a higher risk of developing cancer than do children who were conceived naturally, new research shows.
While the study found the risk of cancer was increased by 42 percent for Swedish youngsters conceived with IVF, the absolute risk of cancer was still quite low.
"We found a roughly 50 percent increased risk for cancer in the IVF children, which means that if the risk without IVF is two per 1,000, it increases to three per 1,000 after IVF," explained study author Dr. Bengt Kallen, a professor emeritus in embryology at the Tornblad Institute at the University of Lund in Sweden.
The findings will be published in the August print issue of Pediatrics, but were posted online on July 19.
In vitro fertilization (IVF) is an assisted reproduction technology. Using eggs harvested from the prospective mother and sperm given by the prospective father, doctors can create human embryos that are then implanted into the mother's uterus.
Babies born using this technology are known to have an increased risk of birth defects and of birth complications, such as preterm birth. Previous research has also suggested that children born through this method of conception may also have an increased risk of cancer.
Using the Swedish Medical Birth Register, the researchers gathered information on almost 27,000 children who were born using IVF in Sweden from 1982 through 2005.
When they looked at the number of children who had cancer, they found that 53 children born from IVF had developed cancer compared to the expected rate of 38 cases of cancer in non-IVF children.
Other factors appeared to influence the risk of cancer as well. Children born before 37 weeks' gestation and those with a low birth weight, respiratory problems or a low Apgar score (a test given at birth to assess a newborn's health), had higher rates of cancer.
A mother's age, weight, smoking status and the number of miscarriages she'd already had didn't appear to affect a child's cancer risk. A multiple birth pregnancy also didn't appear to affect the risk of cancer.
Cancers of the blood, such as acute lymphoblastic leukemia, were the most common, affecting 18 children. The next most common were cancers of the eye or central nervous system, affecting 17 children.
Although it's not clear what's to blame for the increase, the study authors think it's unlikely that IVF is at the root of the increased risk of cancer.
"This study is interesting and thought-provoking, and it adds to our growing knowledge of potential IVF consequences," said Dr. David Cohen, chief of reproductive medicine at the University of Chicago.
"But, it's difficult to think what the biological plausibility would be. If it were something that occurs during the in vitro process or some substance in the media used, I would think that it would cause a much higher number of cancers. This may just be a statistical oddity," he added.
"This is the largest study that I'm aware of, and it does suggest an increased risk of childhood cancers ... but it doesn't really delineate whether it's the IVF process or the patient selection. Is this increase due to the procedure, or is it secondary due to a difference in the patient population?" said Dr. Edward Illions, a reproductive endocrinology specialist at the Montefiore Medical Center in New York City and the Montefiore Institute for Reproductive Medicine in Hartsdale, N.Y.
The three experts do not believe these findings will have a significant influence on a couple's decision to have the IVF procedure.
"The absolute risk is so small that it will hardly influence the decision to get an IVF," Kallen said.
"This adds more information to the [pre-IVF] counseling session, but I don't think it will change the decision. The absolute risk is still well less than 1 percent," said Cohen.
Learn more about in vitro fertilization from the American Pregnancy Association.
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