A certain kind of in-vitro fertilization used for male infertility is linked to a small increased risk of intellectual disability, according to an international study published on Tuesday.
The research in the Journal of the American Medical Association is described as the largest of its kind and was based on the records of 2.5 million children born in Sweden from 1982 to 2007.
Researchers in Britain and the United States focused on 30 959 (1.2%) of those children who were born following an IVF procedure, and looked at diagnoses of autism and intellectual disability.
Overall, when compared to children born from spontaneous conception, children born from any IVF treatment were at no higher risk of autism and an 18% higher risk of intellectual disability, their analysis found.
This risk however disappeared when researchers factored in the potential problems associated with multiple births, which are common in IVF.
Intracytoplasmic sperm injection
Researchers also compared six different types of IVF procedures available in Sweden and whether fresh or frozen embryos were used.
The only procedure that stood out was called intracytoplasmic sperm injection (ICSI), a technique to remedy male infertility that involves injecting a single sperm into an egg.
Children born after that procedure, whether via fresh or frozen embryos, were at a 51% higher risk for intellectual disability than those born after other types of IVF, or a rise from 62 cases to 93 cases per 100 000.
ICSI was developed in 1992; it is recommended for male infertility and is used in about half of all IVF treatments, the researchers said.
"When we separated the different IVF treatments, we found that 'traditional' IVF is safe," said Sven Sandin, co-author of the study from King's College London's Institute of Psychiatry.
"But IVF involving ICSI, which is specifically recommended for paternal infertility, is associated with an increased risk of both intellectual disability and autism in children," Sandin added.
The study noted that "the prevalence of these disorders was low, and the increase in absolute risk associated with IVF was small", and that further research should be done to test associations in other populations.
About 5 million children have been born as a result of IVF worldwide between 1978 and 2012.
Marcelle Cedars, a doctor at the University of California-San Francisco, said in an accompanying editorial that the "data are reassuring regarding the absence of risk of autistic disorder and the small absolute risk of mental retardation".
However, he urged more study of the implications of IVF.
"The number of children born as a result of IVF will continue to increase and much remains to be learned about the long-term implications. Understanding and eliminating even a small risk of neurodevelopmental impairment are important goals."