Children conceived by ICSI (intracytoplasmic sperm injection), the IVF treatment of choice when the man is very infertile, may suffer some development problems at around one year.

Some ICSI babies fared less well in standard development tests than babies conceived by routine IVF (in-vitro fertilisation) or who were conceived naturally.

Researchers from Sydney University, who made the discovery, say it is essential that ICSI children are reassessed as they begin school to see if they are at increased risk of intellectual impairment or learning difficulties.

Although the ICSI children suffered no major health problems in their first year nor had any congenital malformations, their performance was significantly lower than other groups of children when they were assessed for their developmental abilities. Of the 89 ICSI children tested, 17 per cent showed mild to significant delayed development compared with just 2 per cent of the 84 children conceived by IVF, and 1 per cent of the 80 children conceived naturally.

ICSI was introduced as a new form of IVF treatment in 1993, and has quickly become the treatment of choice in many clinics around the world. The Sydney study is the first to assess the long term outcome of these children (Lancet, 1998; 351: 1529-34).

In a commentary alongside the research, specialists from Utrecht University Hospital say that "manipulation of human embryos and intervening with the natural process of conception may induce subtle, complex and far reaching changes in the genetic material of the offspring and also of the next generation."