The study also found that couples who eventually conceived naturally after a least a year of trying, a group doctors call "subfertile," had a risk of having a baby with a birth defect that was about 40% higher than couples with no fertility problems. The risk seen in subfertile couples was also nearly equal to the risk seen in couples who used any assisted reproductive technology (ART) to conceive.
Still, one expert puts the risk into perspective, saying while the overall risk for birth defects due to assisted reproduction may be higher, the real risk is still just somewhat higher than that for a couple having a baby through unassisted conception. Another doctor even called the research "reassuring."
"People who receive ART are having fertility problems, and that does raise the risk of malformations in the infant by itself, because people are having trouble, and there could be some genetic or hormonal reason they would have an increased risk," says Alfred A. Rimm, PhD, a professor of epidemiology and biostatistics in the School of Medicine at Case Western Reserve University in Cleveland, Ohio.
Rimm studies the risk of birth defects associated with ART, but he was not involved in the current research.
The study, which is published in the New England Journal of Medicine, is one of the largest to ever look at the relationship between fertility treatments and birth defects.
It linked 16 years of data -- from 1986 to 2002 -- on all infertility treatments at two clinics in South Australia to a registry of more than 300,000 births and 18,000 birth defects.
Researcher Michael Davies, PhD, MPH, an associate professor at the University of Adelaide in Australia, declined to mention specific types of defects, saying they are looking more deeply into that in his forthcoming research.