Babies born after IVF treatment appear four times more prone to a rare childhood illness, geneticists said last night.

Assisted reproduction might predispose children to birth defects and some cancers, according to researchers in Birmingham, Cambridge and Cardiff.

The warning that a genetic "imprinting disorder" might be responsible for an increased risk of Beckwith-Weidemann syndrome (BWS) could have repercussions for the way IVF and related techniques are performed, and reinforce ethical, safety, and legal arguments against cloning. The human fertilisation and embryo authority is studying the findings, published in the Journal of Medical Genetics.

The report accepted more research was needed but said long-term health monitoring of children born after IVF should be introduced quickly.

Children with BWS have an abnormally large body and tongue, and one side of the body grows quicker than the other. They might have defects in their abdominal wall, hearing and speech problems, and difficulty swallowing. One in 10 develops childhood cancer.

The condition results from errors in genes which undergo imprinting, a phenomenon that means certain genes act differently depending on whether they are inherited from the mother or the father.

IVF seems to interfere with this. BWS normally affects between two and five children in 100,000. The study looked at 149 children with BWS and found six, 4%, were born either after IVF or a related technique called intracytoplasmic sperm injection.