A new study by the U.S. Centers for Disease Control and Prevention (CDC) has found that children conceived with assisted reproductive technology (ART) are two to four times more likely to have birth defects as compared to naturally conceived infants. The findings were applicable only in single births and not in the case of twins or multiple births.

ART refers to a procedure where the eggs are surgically removed from a woman’s womb and combined with sperm in the laboratory and then returned to the woman’s body. In-vitro fertilization is a procedure that is included in the process. The use of only fertility drugs was not examined in this study.

In an agency news release Jennita Reefhuis, an epidemiologist at the CDC's National Center on Birth Defects and Developmental Disabilities said, "Today, more than one percent of infants are conceived through ART, and this number may continue to increase. While the risk is low, it is still important for parents who are considering using ART to think about all of the potential risks and benefits of this technology."

Dr. Reefhuis added, “I think it is important for couples to consider the fact that there may be a risk for birth defects,” in the study published online on Sunday by the journal Human Reproduction.

In the study researchers compared data from 14,095 naturally conceived births to 281 ART conceived births and they also used information already collected by a large project paid for by the government, the National Birth Defects Prevention study. The researchers found that ART resulting in a single birth had twice the risk of birth defects. This included twice the risk for heart defects, more than twice the risk for cleft lip with or without cleft palate, and more than four times the risk of certain kinds of gastrointestinal defects.

Dr. James A. Grifo, director of the fertility clinic at New York University Medical Center, said, “The good news is that the risk is low.” He added that more research was needed to test the findings as the study used a small group of women. “The results are concerning, but with this small a sample of patients, a bigger study would need to be done,” Dr. Grifo said. “And the fact that they see it in singletons, not in twins, makes it hard for me to think this is a direct relationship.”

Dr. Alan R. Fleischman, vice president and medical director of the March of Dimes, said, “I think it’s an important study. It’s confirmatory of the direction we have been concerned about, an increase in some structural birth defects in babies born with assisted reproductive techniques compared to those born without such. And yet the numbers are still small, the risks are low.” Dr. Reefhuis said though the study established a connection between birth defects and ART, it was not clear whether the procedures increase the risk for birth defects, or whether infertility itself raises the risk.