Power calculations are based primary outcome: exclusively breastfeeding duration and made to show effect on exclusively breastfeeding duration between the intervention- and the control group. Requirements for power calculation are a mean value of the vacuum set at 100% with a standard deviation (SD) of 26%. To detect the smallest clinically relevant difference of 13%, equivalent to half a SD and with an expected drop out of 20%, which included 200 infants (100 infants in each group) in the study (alpha = 0.05 and beta = 0.1 ). There hospitalized annually on average 300 preterm infants in the neonatal section. It is expected about 100 infants to meet the criteria for inclusion, thus achieved at approximately 2 year.