The technique is used when a known male infertility problem prevents normal fertilisation from occurring. It has led to the birth of many health babies. Dr Gerald Schatten and colleagues at the Oregon Regional Primate Research Centre examined rhesus monkeys conceived using the technique. They used imaging to watch the fertilisation process, and saw irregularities in the way the egg was fertilised. Writing in the journal Nature Medicine, they warn that the technique might itself damage the chromosomes which carry the genes - the building blocks of life.
Chromosomal damage can cause birth defects, including mental retardation.
Birth defects Out of 14 attempts, five rhesus monkeys were born. Dr Schatten's team was, in fact, trying to show that their technique might work for preserving endangered species. They also noted that some infertile men had genetic irregularities that could contribute to their infertility - the idea being that nature protects the gene pool from these defects by preventing conception in the first place. If they had babies conceived by ICSI, the babies would inherit the defect. And last summer a report in the Lancet medical journal said ICSI babies were a little more likely to show mild delays in mental development.