According to a new study released by the Centers for Disease Control and Prevention, birth defects are more common in babies conceived through fertility techniques such as assisted reproductive technology (ART) than in babies conceived naturally. But the overall risk is still relatively low, the study authors say.

In vitro babies are two to three times more likely to be born with septal heart defects (a “hole” in the heart), said Jennita Reefhuis, Ph.D., an epidemiologist at the CDC's National Center on Birth Defects and Developmental Disabilities. The research found that babies conceived through fertility techniques had more than twice the risk to be born without cleft palate or with cleft lip, and had four times the risk of two gastrointestinal defects.

The defects remain rare in these babies even with the increased risk. For example, the risk of a baby being born with a cleft lip is about 1 in 950 when conceived naturally. The same risk in a baby conceived via fertility treatment would be at a rate of 1 in every 425 births.

The researchers compared 281 births using ART with more than 14,000 naturally conceived births. The babies were born from October 1997- December 2003 in 10 states including Arkansas, California, Georgia Iowa, Massachusetts, New Jersey, New York, North Carolina, Utah and Texas. They looked at approximately 18 categories of birth defects, but only four were found to be statistically significantly associated with fertility techniques. The study did not include women who only took fertility drugs and did not have procedures performed. It did not evaluate artificial insemination or hormone treatments.

The study findings are published in the journal Human Reporduction.

“I think it's important for people to be aware that there may be an increased risk for birth defects with ART,” said Jennita Reefhuis, lead-author of the study. “But it is also really important for couples to realize that with any pregnancy, there is a 3 percent risk of a birth defect regardless of any exposures during pregnancy.”

Reefhuis said any couple considering fertility treatments should understand the risk of birth defects. Researchers said that in vitro fertilization did not increase the likelihood of birth defects among multiple-birth children.

ART is defined as any technique that uses eggs surgically removed from a woman’s ovaries, combining them with sperm in the laboratory, and returning them to the woman’s body or donating them to another woman. The procedure has been used in the US since 1980, and the number of infants born after ART doubled from 1996 through 2004. It is estimated that more than 1 percent of babies born in the United States are conceived using ART. About 12 percent of women (7.3 million) in the United States aged 15-44 had difficulty getting pregnant or carrying a baby to term in 2002, according to the National Center for Health Statistics of the Centers for Disease Control and Prevention.

Other researchers said the study was small and more research was needed to confirm the findings.