Nov. 17 (Bloomberg) -- Certain birth defects multiplied and in some cases more than quadrupled when children were conceived through in vitro fertilization and similar techniques, according to the largest U.S. study of the abnormalities.

Two times the number of some heart abnormalities occurred among infants born using the techniques, called assisted reproductive technologies, in which both eggs and sperm were handled, the U.S. Centers for Disease Control and Prevention said today in the report. Cleft lip cases more than doubled. The risk of gastrointestinal defects was at least fourfold.

Even so, the overall risk of defects from the technique remains low, researchers said. Assisted reproductive technology, or ART, has been used since 1981 to help women become pregnant by surgically removing eggs from ovaries and combining them with sperm in a laboratory. The number of babies born as a result doubled from 1996 to 2004 and now account for more than 1 percent of all births in the U.S., according to the CDC.

It's ``important for parents who are considering using ART to think about all of the potential risks and benefits of this technology,'' said Jennita Reefhuis, an epidemiologist at the CDC's Center on Birth Defects and Developmental Disabilities, in a statement.

Today's report, published in the journal Human Reproduction, drew on information collected from 30,000 infants. The study by the Atlanta-based CDC didn't evaluate artificial insemination or hormone treatments.

To contact the reporter on this story: Tom Randall in New York at trandall6@bloomberg.net.

Last Updated: November 17, 2008 14:03 EST