An IVF birth more than doubles the likelihood of a child developing asthma, research has shown.
In the most extreme cases the risk is increased almost five times, according to new study findings.
Children conceived with artificial help are also more likely to wheeze or take anti-asthmatic medicines by the age of five.
Scientists discovered the link after analysing data on 18,818 children from across the UK born between 2000 and 2002.
But they point out that the association may not be causal, and the chances of a child conceived after IVF treatment becoming asthmatic are still slim.
Researchers conducting the UK Millennium Cohort Study compared children in different groups with those born after natural planned pregnancies.
Children born to sub-fertile parents were 39% more likely to be experiencing asthma symptoms by the age of five and 27% more likely to wheeze.
Closer study showed that the association was mainly driven by children conceived via some form of assisted reproduction technology (ART). This includes IVF (in-vitro fertilisation) and ICSI (intra-cytoplasmic sperm injection) which involves injecting sperm directly into eggs.
However, only 104 children fell into this category, leading the scientists to urge caution when interpreting the results.
The findings are published today in the journal Human Reproduction.
Lead researcher Dr Claire Carson, from Oxford University, said: “Childhood asthma is a common condition in the UK where the prevalence of the condition is higher than other European countries, and to our knowledge this is the first UK study of asthma after IVF conceptions.
“Our analysis suggests that it is the ART group in particular who are at higher risk.”
There could be a number of possible explanations for the link between infertility, IVF and asthma, say the researchers. The scientists took account of mothers’ asthma and smoking history, body mass index (BMI), socio-economic status, the presence of furry household pets and other factors that could have swayed the findings. But they acknowledge there could be other confounding influences.
In the paper they wrote: “Children born after ART have a much higher risk, though we cannot determine if this is indicative of a treatment effect or related to a greater degree of sub-fertility in this group of parents.
“If the observed association is causal, then the mechanism driving it remains unknown and further research in this area is warranted.”
Dr Carson said it was important to remember that in absolute terms the extra number of IVF children developing asthma was small.
“It isn’t much higher than the one in five risk for all children in the UK,” she added.
Malayka Rahman, from the charity Asthma UK, said: “This study suggests that there might be an association between IVF treatment and asthma developing in children, but the sample size for this study is small and currently the research in this area generally is not conclusive.
“Overall research suggests that the absolute risk of asthma increasing after IVF appears to be small. Further work is needed to establish what might be causing this association and whether there are other factors at play other than the IVF treatment itself. In the meantime those considering IVF should speak to their GP about the benefits and health risks in order to make an informed decision.”