Constipation in a premature baby can be helped by encouraging them to drink more fluids. You can also give them small amounts of baby water in addition to their milk. If the situation persists, you can consider giving them PEG-3350, which is a powder that can be dissolved in a small amount of liquid. It is sold in pharmacies under various brand names like Lax-A-Day and Restoralax. Consult with your pharmacist to determine the appropriate dose based on your baby's weight and to learn how to measure the quantity. If you have any further questions, feel free to ask your pharmacist or a healthcare provider.