The intra oral vacuum of the premature infant is assessed by measuring the vacuum in the unit of mBar and are primary made by the project manager which is blinded to know if the infant has received oral stimulation or not. The measurement is made when the infant is awake and show readiness to suck. For vacuum measurement is a manometer selected with a bottle pacifier, which fits a Calmaflaske made by the firm Medela. The pacifier is shaped and is similar in function a breast and extra small so that it matches the premature mouth of a premature infant. As in a completely closed system the sucking of the infant is registered on this connected manometer. In order to obtain a measure of reproducibility of the method all vacuum measurements is carried out at 3 consecutive measurements. The advantage of the 3 measurements within a short time is to determine the intra-individual variability, but only if the infant is motivated and show redlines for measurement 3 times. The equipment is developed in cooperation with the Technical University of Denmark.