Babies born to women who took folic acid late in pregnancy may be more likely to develop asthma, it was claimed yesterday. A study found a 30 per cent increased risk for children whose mothers took supplements of the vitamin between weeks 30 and 34 of their pregnancy. Australian researchers believe the link might explain a rise in asthma among children in developed countries.

But British experts were sceptical, saying folic acid supplements were vital in early pregnancy to prevent birth defects like spina bifida. The study comes after the Government's food watchdog last month ruled that folic acid should be added to all bread. Women hoping to become pregnant are advised to take a 0.4mg supplement of folic acid every day after stopping contraception and for the first 12 weeks of pregnancy, but not beyond.

Experts at the University of Adelaide studied 557 expectant mothers and how many of their children had asthma at 3.5 years and 5.5 years. The findings showed a link with folic acid taken in later pregnancy, but no association with it taken in early pregnancy. But Terence Stephenson of the Royal College of Paediatrics and Child Health cast doubt on the study, saying the increased risk, if there was any, was 'only just statistically significant'.