HeSVA aims to assess how being born preterm at very low birth weight (less than 1500 g) affects adult health and well-being, and how individuals born preterm at very low birth weight transition to adulthood to become independent members of society. The original cohort consisted of over 300 infants born weighing less than 1500 g in the Uusimaa district (Finland) between 1978 and 1985 and treated at the neonatal intensive care unit at Helsinki University Central Hospital. The study later included 172 control participants born at term at the same time and hospital. Baseline data included the participants' health records at birth, and participants have been followed up several times since: at 15 months, 5 years, 18 to 27 years, 20 to 29 years and 22 to 30 years.