A new study of 1000 babies born following the fertility treatment ICSI (intracytoplasmic sperm injection) was reported in the journal Human Reproduction last week. The researchers, based at the Sahlgrenska University, Goteborg, Sweden, found that the technique did not increase the risk of congenital conditions - with one exception. The number of babies born with hypospadias, a condition that affects the penis, was three times higher than expected. Dr Ulla Britt Wennerholm, who led the study, said that hypospadias appears to be associated with paternal fertility problems, so a direct link with ICSI was possible.

ICSI involves taking a single sperm, and injecting it directly into an egg in vitro. Some doctors have expressed fears that the egg may be damaged during the injection process, or by the chemicals used for ICSI. Others are concerned that selecting a single sperm bypasses the usual competition amongst sperm to fertilise the egg. This could lead to fertilisation with a 'substandard' sperm, which would not have succeeded if it had not been injected. But these fears have so far proved unfounded: ' About 20,000 babies have been born world-wide through ICSI in the last decade, and the vast majority of these are normal, healthy children' said Dr Wennerholm.

Although the number of children in the study affected by a congenital condition was higher than usual, Dr Wennerholm believes this is due to a higher incidence of prematurity, caused by a greater number of multiple births. The only condition that was overrepresented in the group was hypospadias, with seven cases instead of the expected two. ICSI has only been in use for the past nine years, so it is too early to tell whether or not boys born as a result of the technique will inherit their father's fertility problems.