IVF treatments that require the direct injection of sperm into the egg are associated with a small increased risk of intellectual disability in the resulting children, according to a study.

Scientists also found that standard IVF treatment posed no increased risk of children developing intellectual disabilities or autism.

IVF is considered generally safe. About 4% of IVF children have physical or mental problems at birth, compared with 3% of those conceived naturally.

In the latest study, the largest so far into links between reproductive treatments and neurodevelopment, scientists examined how IVF might affect the incidence of autism and intellectual disability.

In particular they looked at the effects of a type of IVF that involves intracytoplasmic sperm injection (ICSI), used when the potential father has a very low sperm count or other fertility problems.

In this procedure, sperm is extracted surgically from the testicles and injected straight into the egg, in order to increase the chance of conception. Around half of modern IVF procedures involve ICSI.

The study by Avi Recheinberg, of the Kings College London Institute of Psychiatry, and colleagues from the Karolinska Institutet in Sweden looked at data on 2.5 million children born in Sweden from 1982 to 2007, of which 30,959 were born as a result of IVF.

The results, published in the Journal of the American Medical Association, showed that more children were born with an intellectual disability after IVF treatments involving ICSI compared with standard IVF. The absolute numbers were very small: an increase in cases from 62 to 93 cases per 100,000 children, representing a relative increase in risk of around 50%.

The scientists also found an increased risk of autism after ICSI, from 29 to 136 cases per 100,000, but this result disappeared when other factors that could play a part, such as multiple births, were taken into account.

Allan Pacey, a fertility expert at the University of Sheffield and chairman of the British Fertility Society, said the main message of the paper was a positive one, suggesting that any risk of these disorders was 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. He advised patients not to worry and to discuss any concerns they had about their treatment with doctors.

Dagan Wells, of the Institute of Reproductive Sciences at the University of Oxford, agreed that the results of the study should be reassuring for patients undergoing IVF treatment.

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.