Babies born before 37 weeks of pregnancy need special care. Many times they cannot eat, as they are not able to suck. So tube feeding will be done while they are in the hospital in the incubator.
In addition, being in the incubator will help the premature baby to maintain their body temperature and stay warm, as they are usually born somewhat cold.
Sometimes a system is also needed to help their breathing if their lungs are not yet perfectly formed.