A one piece pre-cut ostomy system consists of a bag and an attached barrier that cannot be separated. The wafer has a circular hole already cut out of it for your stoma to fit through. This prevents you from having to cut a hole in the ostomy wafer yourself. You can choose from several different opening sizes to best fit your stoma. This type of pouch is ideal for people who have a round, evenly shaped stoma. Pre-cut ostomy pouches are not ideal for people who have recently had ostomy surgery, because the stoma may be swollen or change shape.