By Michelle Roberts
BBC News health reporter in Copenhagen
Fears that children born using a form of IVF introduced in the 1990s will suffer from lower IQs are unfounded, say Belgian researchers.
There have been concerns about ICSI
Intra-cytoplasmic sperm injection (ICSI) involves injecting a single sperm directly into an egg.
Eight-year-old children born using ICSI were found to be just as intelligent, if not more so, as other children.
The Vrije University study was presented at a European fertility conference in Denmark.
Just under half of all IVF treatments carried out in Britain now use the ICSI procedure, often to get round male fertility problems.
More than 3,000 children a year are now born as a result of ICSI.
However, there were concerns that the process bypassed the natural safeguards put in place to prevent sub-standard sperm from fertilising the egg.
Early studies, conducted only a year after the first ICSI children were born, suggested that their development might be delayed.
The new results, by psychologist Lize Leunens and colleagues, should allay such fears.
Even if the children were held back as babies, by age eight they had more than overcome any such cognitive handicaps.
The researchers compared 151 ICSI children with the same number of children who were naturally conceived.
The children were given a variety of intelligence tests covering verbal, arithmetical, memory and mental performance skills.
The ICSI group had an average IQ score five points higher than the non-ICSI group - an IQ of 112 compared with 107, respectively.
While significant, the researchers stressed that this might be down to parenting style rather than ICSI itself or inherited IQ.
Lize Leunens said: "We hypothesise that these mothers have already pursued certain goals in their careers and are now more dedicated to parenting, and therefore might stimulate their children more than the mothers of the control group.
"This is a very wanted child. They have waited for the child for many years," she told the European Society for Human Reproduction and Embryology annual meeting.
"This is reassuring news. We can be pretty sure that in the long term these children are not suffering any developmental delays."
A spokesman for the Human Fertilisation and Embryology Authority, the body that regulates fertility treatment, said: "This new study is bound to provide reassurance to parents who had children through ICSI.
"We will continue to monitor all the evidence on ICSI as it comes in."