Certain forms of IVF treatment are significantly associated with an increased risk of low intelligence in children, a major study has shown.
Of the total number of children born between 1982 and 2007, almost 31,000 were conceived using IVF
A link was also found with an especially severe type of autism, but only in the case of twins or triplets.
Scientists, who analysed data on more than 2.5 million births, stressed that the chances of an IVF baby being affected remained tiny in real terms.
They found a 51 per cent increased risk of intellectual impairment, marked by an IQ below 70, in children conceived by IVF treatments in which sperm cells are injected directly into eggs.
This amounted to a rise from 62 per 100,000 children (0.062 per cent) to 92 per 100,000 (0.092 per cent).
But the researchers said the result could not be explained by factors such as premature and multiple births and needed further investigation.
The direct injection method, known as Intra-Cytoplasmic Sperm Injection (Icsi), was developed to help infertile men, but it now makes up half of IVF treatments in the UK, including those resulting from female fertility problems.
In rare cases Icsi treatments are carried out using sperm that is surgically extracted. This procedure led to a more than four-fold increased chance of a child developing a severe and highly disabling form of autism.
The association vanished when multiple births were taken into account, leading scientists to suspect that some factor other than the Icsi procedure was responsible.
The Swedish study, published in the Journal of the American Medical Association, is the first of its kind to compare a wide range of IVF treatments.
Of the total number of children born between 1982 and 2007, almost 31,000 were conceived using IVF. They were followed up for an average of 10 years until 2009.
Of the 16,000 children diagnosed with intellectual impairment, 180 were IVF babies. Seven thousand children developed severe autism, of which 103 were born after IVF.
Compared with ‘natural’ conception, IVF overall had no effect on autism rates and led to a very small 18 per cent increased risk of low IQ which appeared to be linked to multiple births.
The significant findings only emerged when researchers compared six different types of IVF involving the standard ‘mixing-in-a-dish’ method of fertilising eggs or Icsi.
Icsi used with fresh or frozen embryos produced 51 per cent more intellectually impaired children than standard IVF.
Study leader Avi Reichenberg, from the Institute of Psychiatry at King’s College London, said: “Our study shows that treatments developed to manage male infertility are associated with an increased risk for developmental disorders in offspring.
“The exact mechanism is unclear, but there are a number of risk factors, from selection of IVF procedures, to multiple embryos, and to pre-term birth.
“While intellectual disability or autism remain a rare outcome for IVF, being aware of the increased risk associated with specific types of IVF means offspring at risk can be identified and potentially monitored for developmental disorders, ensuring they receive early detection and appropriate support and care.”
The researchers insisted the research should not hinder childless couples seeking IVF treatment.
Co-author Karl-Gosta Nygren, from the Karolinska Institute in Stockholm, said: “There’s no question that we would stop any treatment or anything like that because of the findings. On the contrary, the results are reassuring.”
He pointed out that the increased risk of birth defects associated with IVF was much higher.
“It’s important to remember that the majority of children are born perfectly healthily following IVF,” he added. “Our study provides much-needed information for parents and clinicians on the relative risks of modern IVF treatments, enabling them to make the most informed choice possible.”
The number of couples seeking IVF treatment has soared in industrial countries in recent years. In 1992, 0.3 per cent of children born in the UK were conceived through IVF. By 2010 this figure had risen to two per cent.
Allan Pacey, senior lecturer in reproductive and developmental medicine at the University of Sheffield and chairman of the British Fertility Society, said: “This is a very important study which defines the risks of IVF children being born with two neurodevelopmental disorders.
“It is a large study and is exactly the kind we need if we are to give patients accurate information before they embark on treatment.
“The main message of the paper is a positive one, suggesting that any risk of these disorders is very low, or absent, in comparison to children conceived naturally. However it does highlight the importance of preferentially using standard IVF rather than Icsi, and also using ejaculated sperm rather than those recovered surgically from the testicle, in situations where it is possible to do so.
“Patients about to embark on treatment should not worry and should discuss any concerns about their treatment plan with the team responsible for their care.”
Dagan Wells, from the Institute of Reproductive Sciences at Oxford University, said: “In general, the results of the study should be reassuring for patients undergoing IVF treatment. They show that risks of problems such as autism and mental retardation remain low following infertility treatments.
“Assessing the long-term effects of treatments such as IVF is difficult. Technologies are constantly evolving and changing, presenting a moving target for doctors and scientists. A limitation of this study is that some of the data comes from treatments carried out 30 years ago, when IVF was in its infancy.
“The methods used today differ significantly from techniques used decades ago. Whether they are more or less safe remains to be seen.”