STUDY 3 / randomized INTERVENTION STUDY / ORAL STIMULATION Infants whose mothers is included in the cohort is randomized to receive / not receive oral stimulation when the infant's postnatal age is at least 32 + 0 weeks, as it is the time when the infant is able to coordinate sucking and swallowing reflex. In multiple birth all infants is randomized to the same group. The list is generated block randomized in blocks of 10