Study design
Participants will be contacted using details from the 15-year assessment of the cohort. The first phase will be to complete a respiratory questionnaire at home. The second phase will be to attend the Health Sciences Building in Aberdeen for a clinical assessment which includes spirometry, exhaled nitric oxide, height and weight measurements, blood pressure measurement and taking blood.
Recruitment
The database from the 15 year assessment will be used to contact participants by post. Non-respondents will be contacted a second time by post. We will ask staff in Data Management at the University of Aberdeen to identify and anonymously pass on letters of invitation to participants who do not respond to the second mailing.
Participants will be asked to complete a respiratory questionnaire (online or by paper). We anticipate approximately 700 of the original cohort members to actively take part in this study and to get a more complete dataset, we will seek approval from the Grampian Safe Haven and Information Service Division to link the SEATON cohort to GP prescribing to identify those children who have developed asthma (identified by receipt of inhaled steroids).
Questionnaires
The same respiratory questions used at five, ten and 15 years will be asked again to ensure consistency. Participants who return the questionnaire will be invited to take part in the clinical assessment.
Clinical assessment
First height, weight and waist circumference will be measured using standard and calibrated equipment in the Health Sciences Building at Foresterhill. We will then use total body impedence technology to ascertain total body fat and lean mass. Next, exhaled nitric oxide will be measured using the standard methodology; exhaled NO is elevated in allergic airway disease and is measured on three slow exhalations.
The participant will be given the opportunity to complete the Hospital Anxiety and Depression questonnaire.
Spirometry will be measured next using out standard operating procedure (SOP); in accordance with international guidelines. The best of three technically acceptable measurements will be recorded.
Blood will be collected to determine total IgE and IgE specific to house dust mite, cat dander and grass pollen.
For participants where we have no DNA sample (due to no prior participation or only a small sample previously being obtained) we will collect a sample of saliva for later DNA extraction.
Power and sample size
The sample size is determined by the initial number recruited and the proportion who are prepared to participate at 25 years of age. The SEATON cohort is one of five Uk birth cohorts whose data are being combined so the sample size for the wider analysis will be many 1000s once all cohorts are considered.
Statistical analysis
We will use the same approach as previously. Our initial analysis will relate maternal diet during pregnancy and fetal measurements to asthma and related outcomes at 25 years whilst adjusting for confounder such as parental asthma, gender and socioeconomic status.