Saliva collection in a feasibility study for a new UK birth cohort

In longitudinal birth cohort studies, collecting DNA samples enables researchers to understand the interplay between biology and social environment and doing so at the baseline wave of a study provides an opportunity to genotype children and parents before subsequent attrition takes place. However, collecting saliva samples for DNA extraction at the first wave has not yet been tested in the UK, and it is unclear what the impact on overall recruitment to a longitudinal study would be. In order to test the impact of saliva collection on recruitment at an initial wave, a randomised subsample of families was asked to provide saliva for DNA extraction in the Early Life Cohort Feasibility Study (ELC-FS).

ELC-FS collected information about several thousand babies aged between 8-12 months old, and their families in 2023-2024 in order to test the feasibility of conducting a new UK-wide birth cohort study. It is led by the Centre for Longitudinal Studies at University College London with interviewing carried out by Ipsos. Interviews were carried out using web, phone and video-interviewing as well as face-to-face, and mothers and fathers (including those living in their own households) were recruited directly and separately.

In the ELC-FS, saliva consent and collection could be administered in-person or remotely, and saliva was collected (if consented) for each biological parent as well as the cohort child. We discuss the qualitative testing conducted ahead of fieldwork to test materials and acceptability of this, and we present results on the survey response rates, saliva completion rates for parents and babies, and sample quality. We found variation in completion rates across key sociodemographic subgroups; we present findings from work with public advisory groups conducted in early 2026 that aimed to understand reasons for differential saliva consent rates among ethnic minority groups, to improve take-up in the future.