Planning for discharge begins on the day your baby is admitted to the NICU. Together with the nursing staff, the neonatologists teach and keep you informed about problems your baby is experiencing. As your baby’s condition improves, you will be encouraged to participate in the daily routine care of the baby. This will help you prepare for your baby’s discharge. Before your baby can be discharged home, several requirements have to be met:

1. baby has to be able to maintain body temperature in an open crib
2. all feedings from bottle/breast or both have to be well established
3. intake of milk should be adequate for appropriate weight gain
4. baby has to be medically stable without significant apnea (pauses in breathing), bradycardia (slow heart rate) and desaturation events for 4-5 days before discharge. If your baby was born prematurely, the date for discharge will usually be around the original due date. Hospital stays vary from a few days to many months.
http://www.kidshealth.org/parent/newborn/medical/preemie_home.html