Children born after fertility treatments, such as IVF, may have a slightly higher chance of developing asthma, research suggests Thursday. In a study of more than 13,000 UK children, five-years-olds were about twice as likely to have asthma if they were not conceived naturally. The children were also more likely to need medication, which could be an indication of more severe asthma. The findings were published in the "journal Human Reproduction". The researchers, at the Universities of Oxford and Essex, analysed data from children born between 2000 and 2002. Researcher Dr Claire Carson said 15% of all the children in the study had had asthma at the age of five, but this proportion had risen to 24% among the 104 of them born through assisted-reproduction technologies. She said it was interesting that the pattern had emerged, but far too soon to say if IVF treatment resulted in higher rates of asthma. Other explanations, such as genetics, may explain the association. Dr Carson said that parents should not be put off IVF. "Assisted reproduction technologies offer a chance to become a parent when there isn't another option," she said. "For the majority of children asthma is quite manageable."