Factors of non-responsive or lost-to-follow-up Japanese mothers during the first year post partum following the Japan Environment and Children’s Study: a longitudinal cohort study

OBJECTIVES: We examined the factors related to lost-to-follow-up of a birth cohort study during the first year after delivery. DESIGN: Longitudinal cohort study. SETTING: Questionnaires were provided by mail. Mothers answered the questionnaires about the children twice: at 6 months and 1 year. PARTICIPANTS: Of 103 062 pregnancies who consented to participate in the Japan Environment and Children’s Study (JECS), 93 417 mothers were included in the study after excluding those with multiple births, miscarriages or stillbirths and those who withdrew from the study within 1 year after providing informed consent. PRIMARY AND SECONDARY OUTCOME MEASURES: Participants’ socioeconomic status, medical history, health status, health-related behaviours, their children’s health conditions and living situations were collected by self-administered questionnaires during pregnancy or 1 month after delivery as the baseline survey. In addition, two self-administered questionnaires were distributed 6 months and 1 year after delivery. Using the response status of the two questionnaires after delivery, participants’ follow-up status was divided into four groups. The related factors were examined using logistic regression analysis. RESULTS: Factors positively correlated with lost-to-follow-up to the questionnaires were postpartum physical conditions, psychological distress during pregnancy, the child’s health status at birth, the child’s primary caregiver and the number of siblings of the child. Partners’ active participation in JECS was associated with a lower lost-to-follow-up rate to the two questionnaires, whereas inactive participation was positively associated with a higher lost-to-follow-up rate. CONCLUSION: The response rate to the questionnaires seems to be related to the interest and understanding of participants’ partners. In addition, the response rates are related to participants’ physical conditions and living conditions. To decrease lost-to-follow-up rates in consecutive questionnaire surveys within a cohort study, it may be important for investigators to recognise that participants and their motivation in research can be influenced by perceptions they may have regarding the objectives of the research.