NEW ORLEANS -- The use of assisted reproductive technology (ART) -- of which in vitro fertilization is the most common technique -- appears to be associated with higher rates of birth defects, researchers found.
Babies born to mothers who used ART to conceive were more likely to have a major birth defect compared with those born to mothers who conceived naturally, according to Dr. Lorraine Kelley-Quon of Mattel Children's Hospital in Los Angeles, who reported the findings at the American Academy of Pediatrics meeting here. The results held up even after adjusting for potential confounders like maternal age.
In particular, ART was associated with an 81 percent increase in the relative risk for defects of the eye, a 41 percent increase in relative risk for congenital heart defects, and a 40 percent increase in relative risk for defects of the genitourinary system.
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There was, however, almost a 70 percent reduction in the rate of chromosomal abnormalities, according to the study -- a finding that might be explained by a lower threshold for termination among couples using assistance to get pregnant, Kelley-Quon said.
"Our results imply that there may be factors inherent in assisted reproductive technology that increase the likelihood of birth defects," she said during her presentation.
Kelley-Quon acknowledged, however, that it is a challenge for her study and others investigating the same issue to fully account for the effect of the mother's or father's underlying reasons for infertility.
In the current study, the researchers adjusted for maternal age, which is strongly correlated with the risk of birth defects, "but there are conceivably many factors yet to be defined that we're not able to quantify to measure the degree of infertility in an individual," Kelley-Quon said.
The inability to control for the underlying causes of infertility is a key consideration, according to Dr. William Gibbons, a reproductive endocrinologist Baylor College of Medicine in Houston and a past president of the American Society for Reproductive Medicine.
It's accurate, he said in an interview, to tell couples using ART that they have an greater likelihood of giving birth to a child with congenital malformations.
"This is actually not new information, and it's information that I give my patients now," he said.
But he adds that the increased risk of birth defects is in comparison to a population without fertility problems. Studies that have compared infertile couples using ART to conceive with infertile couples that conceive spontaneously have shown little difference in the occurrence of major malformations, except when intracytoplasmic sperm injection (ICSE) is used.
Thus, Gibbons said, much of the increased risk of birth defects in the ART population "may be related to genetic background and being infertile, and we want to study that and learn more about that."
Kelley-Quon and colleagues looked at data from California, the state with the highest number of infants born after ART. They analyzed information from the Office of Statewide Health Planning and Development Maternal/Infant dataset for 2006 to 2007.
The researchers performed separate analyses for babies born after ART, including in vitro fertilization and gamete intrafallopian transfer, and those born following the use of other fertility-related services, including ovulation induction, fertility-enhancing drugs, artificial insemination, or intrauterine insemination.
In an analysis comparing 1,749 babies born after non-ART fertility-related services with 17,748 naturally conceived infants propensity matched on maternal age, parity, plurality, race, gender, and year of birth, there were no differences in rates of various major birth defects.
The analysis of the association between ART and birth defects included 4,795 babies born following ART and 46,025 matched controls. The overall rate of major congenital malformations was significantly higher in the ART group.
In an analysis that separated singletons and multiples, the likelihood of birth defects was higher following ART for multiples only.
Limitations on the number of embryos transferred should be considered, Kelley-Quon said.