Cohort profile: ADEF Helsinki - a longitudinal register-based study on exposure to alcohol and drugs during foetal life.

Purpose: The need for longitudinal studies on prenatal substance exposure (PSE) extending into adulthood is widely recognised. In particular, studies on the dual effect of exposure to substances and adverse childhood experiences are needed. This register-based matched cohort study investigates the effect of this dual exposure on the health and development of youth with PSE. The follow-up is from birth to young adulthood. Participants: The exposed youth were born in 1992-2001 to mothers with a significant substance misuse problem during pregnancy. The mothers were identified in primary care maternity clinics in the Helsinki metropolitan area and referred for intensified pregnancy follow-up in a tertiary care setting (HAL-clinics). Data from hospital medical records were collected for the mothers during the pregnancy follow-up and linked with register data from multiple national health and social welfare registers obtained for each mother-child dyad from birth until the end of 2015-2018. Similar register data were gathered for three matched mother-child dyads without any evidence of the mother's substance misuse in national health and social welfare registers. The study consists of 615 exposed and 1787 unexposed youth aged 15-24 years. Findings to date: A majority of the exposed youth (64%) had been in out-of-home care at least once compared with 8% among the unexposed. Outpatient and inpatient hospital care due to mental or behavioural disorders were two to three times more common among the exposed than among the unexposed. The exposed had less often completed secondary school education and had more often needed social assistance. Future plans: The data comprise a wide range of information on infant health, youth's mental and somatic health and development, out-of-home care history, and mother's life situation at the delivery and later health. Risk and protective factors for different long-term developmental outcomes in adolescence or in young adulthood will be studied.