Couples who have certain types of fertility treatment have a higher chance of having a child with autism or learning difficulties - although the overall risk is still extremely small, scientists said on Tuesday.
The experts said couples should not consider abandoning or avoiding in-vitro-fertilization (IVF) on the basis of their research findings.
The study, conducted by Swedish researchers based in Britain, Sweden and the United States, found children born after IVF treatments for the most severe forms of male infertility were more likely to be diagnosed with autism or an intellectual disability.
But the actual numbers were low - children born after one form of IVF treatment had a 0.136 percent risk of having autism - a developmental disorder characterized by poor communication skills - compared with a 0.029 percent risk for children conceived naturally, they said.
"The main message ... is a positive one, suggesting that any risk of these disorders is very low, or absent, in comparison to children conceived naturally," said Allan Pacey, who was not involved in the research and is a fertility expert at Sheffield University and Chairman of the British Fertility Society.
The study was the largest of its kind and the first to compare all available IVF treatments and the risk of neurodevelopmental disorders in children.
The researchers analyzed more than 2.5 million birth records from 1982 and 2007 and followed up whether children had been diagnosed with autism or intellectual disability - defined as an intelligence quotient (IQ) score below 70 - until 2009.
Of the 2.5 million children, just under 31,000, or 1.2 percent, were born following IVF treatment.
Standard IVF treatment involves an egg being fertilized with sperm in a laboratory dish, while intracytoplasmic sperm injection (ICSI) fertility treatments - now used in about half of cases and often recommended for male fertility problems - involve injecting a single sperm directly into an egg.
"When we looked at IVF treatments combined, we found there was no overall increased risk for autism, but a small increased risk of intellectual disability," said Sven Sandin of King's College London's Institute of Psychiatry, who co-led the study.
"When we separated the different IVF treatments, we found traditional IVF is safe, but that IVF involving ICSI, which is specifically recommended for paternal infertility, is associated with an increased risk of both intellectual disability and autism in children," he told a briefing in London.
MECHANISM IS UNCLEAR
Rates of autism have been rising rapidly in recent years, to around 1 in 100 children in Europe and as many as 1 in 88 in the United States. Since IVF births are also increasing, some researchers have wondered whether the two might be linked.
But Sandin said that while he could not entirely rule out an effect from IVF, it was certainly not the whole answer to why autism rates are going up. "This cannot explain the increased rates we're seeing," he said. "If it does contribute anything, it's a very, very, very small fraction."
The study, published in the Journal of the American Medical Association (JAMA), found that children born after IVF treatments with ICSI had a 0.093 percent risk of intellectual disability, compared with a base risk of 0.062 percent.
Children born after IVF with ICSI using fresh embryos and surgically extracted sperm - rather than sperm ejaculated naturally - had the higher risk of autism.
Avi Reichenberg, who led the study with Sandin at the Institute of Psychiatry and Mount Sinai School of Medicine in New York, said the results showed a link between some IVF treatments a higher risk of developmental disorders in children, but stressed the study did not identify a cause.
"The exact mechanism is unclear, but there are a number of risk factors, from selection of IVF procedures, to multiple embryos, and to preterm birth," he told reporters.
Pacey said doctors and patients should consider preferentially using standard IVF rather than ICSI wherever possible, and also using ejaculated sperm rather than sperm recovered surgically from the testicles.
© 2014 Thomson/Reuters. All rights reserved.