ORIGINAL ARTICLE Reproductive epidemiology Asthma in children born after infertility treatment: findings from the UK Millennium Cohort Study

study question: Is asthma more common in children born after subfertility and assisted reproduction technologies (ART)? summary answer: Yes. Asthma, wheezing in the last year and anti-asthmatic medication were all more common in children born after a prolonged time to conception (TTC). This was driven specifically by an increase in children born after ART. what is known already: Few studies have investigated any association between ART and asthma in subsequent children, and findings to date have been mixed. A large registry-based study found an increase in asthma medication in ART children but suggests under-lying infertility is the putative risk factor. Little is known about asthma in children after unplanned or mistimed conceptions. study design, size, duration: The Millennium Cohort Study is a UK-wide, prospective study of 18 818 children recruited at 9 months of age. Follow-up is ongoing. This study analyses data from follow-up surveys at 5 and 7 years of age (response rates of 79 and 70%, respectively). participants/materials, setting, methods: Singleton children whose natural mothers provided follow-up data were included. Mothers reported whether their pregnancy was planned; planners provided TTC and details of any ART. The population was divided into ‘unplanned ’ (unplanned and unhappy), ‘mistimed ’ (unplanned but happy), ‘planned ’ (planned, TTC, 12 months), ‘untreated subfertile ’ (planned, TTC.12 months), ‘ovulation induced ’ (received clomiphene citrate) and ‘ART ’ (IVF or ICSI). The primary analysis used the planned children as the comparison group; secondary analysis compared the treatment groups to the children born to untreated subfertile parents. Outcomes were parent report of asthma and wheezing at 5 and 7 years, derived from validated questions in the Inter