Children born after infertility treatment are at increased risk for asthma, results of a large cohort study indicate.
The findings add to the growing body of evidence linking subfertility, assisted reproduction techniques (ART), and asthma in children, say the authors, who call for further work to establish causality and elucidate the underlying mechanism.
Claire Carson (University of Oxford, UK) and team analyzed information on children who are participating in the Millennium Cohort Study. This is a UK-wide prospective study of 18,818 children recruited at 9 months of age and followed-up at 5 and 7 years.
The 13,041 children in the present study were divided into six groups according to the circumstances surrounding their conception, based on interviews with their mothers. These groups were: "unplanned" (n=2039; unplanned and unhappy), "mistimed" (n=3645; unplanned but happy), "planned" (n=6575; planned and trying to conceive [TTC] for less than 12 months), "untreated subfertile" (n=505; planned and TTC for more than 12 months), "ovulation induced" (n=173; mother received clomiphene citrate), and "ART" (n=104; in vitro fertilization [IVF] or intracytoplastmic sperm injection).
Approximately 15-16% of children in the study population had asthma, 12-15% had a wheeze, and around 4% used asthma medications.
Reporting their findings in Human Reproduction, Carson et al reveal that children born to subfertile mothers (ie, the latter three groups) were at significantly increased risk for being asthmatic, to suffer wheeze, and to be taking anti-asthma drugs at the age of 5 years, with adjusted odds ratios (ORs) of 1.39, 1.27, and 1.90, respectively.
The increased risk was driven by findings in the ART group, who faced substantially increased risks for asthma, wheeze, and use of anti-asthma medication at age 5 years, with adjusted ORs of 2.65, 1.97, and 4.67, respectively.
The associations persisted at the age of 7 years, but with weaker ORs.
"Our analysis suggests that it is the ART group in particular who are at higher risk," said an accompanying press statement. "However, we do need to be reasonably cautious when interpreting the results because there is a relatively small number of IVF cases in our study - just 104 babies."
Potential explanations for the link between infertility and asthma include a physiologic effect of infertility treatment, over-reporting of asthmatic symptoms by excessively protective ART parents, or subfertility as a marker for overall poorer health or other comorbidities that raise asthma risk.
Carson et al conclude: "If the observed association is causal, then the mechanism driving it remains unknown and further research in this area is warranted."
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