A study of more than 2.5 million children found no link between in vitro fertilization (IVF) and autism, but a slight increase in risk for mental retardation, or intellectual disabilities.
Certain treatments used to specifically target male factor infertility -- in particular, intracytoplasmic sperm injection, or ICSI -- carried higher risks, but the overall risk of children being born with intellectual disabilities, defined as an IQ as under 70, was quite small.
"Autism and intellectual disability remain a rare outcome, and most children born following IVF will be perfectly healthy," said co-author Sven Sandin, a researcher with King's College in London, who previously studied the link between advanced maternal age and autism. The findings were published in the Journal of the American Medical Association on Tuesday.
Researchers analyzed the birth records of 2.5 million children born in Sweden between 1982 and 2007. Those born after IVF -- a process in which an egg and sperm are joined in a lab before implanting the resulting embryo in a woman's uterus -- had an 18 percent higher risk of mental retardation relative to those who were not.
However, the absolute risk was small: Just over 1 percent of the children born after an IVF procedure had intellectual disabilities. And the risk disappeared when researchers focused solely on single births. (Doctors often transfer multiple embryos during IVF, which can significantly increase a woman's chances of having twins or multiple births.)
As for why the risk of mental retardation was slightly higher among babies born after ICSI, in which a needle is used to inject sperm directly into a mature egg, researchers can only guess. Dr. Kathleen Hoeger, director of the Strong Fertility Center at the University of Rochester who did not work on the new study, said one hypothesis is that when inserting the sperm directly into the egg, doctors introduce substances that wouldn't otherwise be present, such as the culture medium in the lab dish.
But even among male-focused fertility interventions, Hoeger stressed that the risk of mental retardation was very low -- under 2 percent.
"In my view, this is a very reassuring study," she said. "There's no significant risk for these types of disorders and low absolute risk with ICSI." Doctors have a responsibility to discuss those risks with women and their partners, and to limit the chance of having multiples, Hoeger added, but most couples end up at IVF because it is their best chance at having a baby together.
The Centers for Disease Control and Prevention estimates that more than 1 percent of babies born in the United States each year are conceived using assisted reproductive technology, a broad umbrella that includes all fertility treatments in which both an egg and sperm are handled. Earlier research has also linked IVF to certain health risks in offspring, including a study presented at the American Academy of Pediatrics' annual meeting last fall, which found that babies have a slightly higher risk of certain birth defects, including those that affect the heart, eye, reproductive and urinary systems.
Experts say the new findings can be extrapolated for a U.S. audience, given that the techniques and equipment used both here and in Sweden are very similar. If anything, the findings are particularly noteworthy for doctors and couples here, argued Hoeger, as ICSI is used more often in the U.S.
On the whole, experts emphasized that the new research is generally reassuring that IVF is safe, but that it should continue to be studied.
"Even though the data are reassuring regarding the absence of risk of autistic disorder and the small absolute risk of mental retardation with IVF," wrote Dr. Marcelle Cedars, a professor and director of the University of California San Francisco Women’s Health Clinical Research Center in an accompanying editorial, "continued study of the implications of ovarian stimulation, embryo culture, and multiple embryo transfer is required."