A baby born at 33 weeks typically stays in the NICU for about 2 to 4 weeks, with many going home close to their original due date or a few weeks before it. The exact timeline depends on how quickly your baby hits a set of specific milestones: breathing independently, feeding by mouth, and maintaining body temperature outside an incubator. Some 33-weekers sail through these in two weeks; others need a bit longer.
Why the Timeline Varies
There is no fixed number of days that applies to every 33-weeker. Discharge is milestone-driven, not calendar-driven. The NICU team watches for a handful of concrete abilities, and your baby goes home once all of them are consistently met. That makes it hard to circle a date on the calendar early on, because progress on one milestone (like breathing) doesn’t guarantee the others will follow on the same schedule.
Birth weight, whether your baby is a singleton or twin, and whether complications develop all shift the timeline. A 33-weeker born at a healthy weight for gestational age with no respiratory issues may be home in under two weeks. A smaller baby who needs breathing support could stay closer to four or five weeks.
Breathing: Usually the First Hurdle
At 33 weeks, the lungs are developed enough to function but may still lack a full supply of the coating that keeps the air sacs open. Some 33-weekers breathe well on their own from birth. Others need supplemental oxygen or gentle air pressure for a few days to a couple of weeks.
A related challenge is apnea of prematurity, where the baby briefly pauses breathing or has a drop in heart rate. These episodes, sometimes called “As and Bs” (apnea and bradycardia), are common in babies born before 34 weeks. The reassuring news is that for babies born at 33 weeks, these spells almost always resolve by 36 to 37 weeks of post-menstrual age, meaning roughly 3 to 4 weeks after birth. About 92% of preterm infants stop having apnea spells by 37 weeks. Most NICUs require a baby to be spell-free for 5 to 7 consecutive days before discharge.
Feeding: The Milestone That Takes Longest
Feeding readiness is often the final gate before going home, and it tends to be the one parents wait on the longest. Babies develop a basic sucking reflex around 32 weeks, but the coordinated pattern of sucking, swallowing, and breathing at the same time doesn’t reliably kick in until about 34 weeks. That means your 33-weeker will likely start practicing at the breast or bottle within the first week or so of life, but full oral feeding can take another one to two weeks of gradual progress.
Until your baby can take all feedings by mouth and gain weight steadily, nutrition comes through a thin tube that runs through the nose or mouth into the stomach. The transition from tube feeding to full oral feeding is rarely a straight line. Your baby might take a full bottle one feeding and then be too sleepy for the next. The NICU team looks for consistent performance over multiple days, along with steady weight gain, before counting this milestone as met.
Temperature Control and the Crib Transition
Babies born at 33 weeks usually start in an incubator (sometimes called an isolette) that maintains a warm, controlled environment. The transition to an open crib typically happens when the baby weighs between 1,500 and 1,800 grams (roughly 3 pounds 5 ounces to about 4 pounds). At that weight, most babies have enough body fat to hold their temperature steady on their own.
For a 33-weeker, this transition often happens within the first one to two weeks. The team will monitor your baby’s temperature for a day or two in the open crib to make sure it stays stable. If the baby struggles to stay warm, they simply go back to the incubator for a bit longer.
Other Common Issues at 33 Weeks
Jaundice is extremely common in moderate preterm babies. The yellowish skin color comes from a buildup of bilirubin that an immature liver can’t clear fast enough. Treatment is phototherapy, where the baby lies under special lights for a day or two. It’s routine and rarely extends the NICU stay by more than a few days on its own.
Low blood sugar in the first hours and days after birth is another frequent issue for 33-weekers. The NICU team checks blood sugar regularly and treats it with extra feedings or, if needed, an IV sugar solution. This typically resolves within the first few days. Infections are possible but less common, and the team monitors for them closely with standard screening.
What Discharge Day Looks Like
Before your baby can leave, the NICU team confirms a checklist of requirements. Your baby needs to be breathing without any support, taking all nutrition by mouth, gaining weight consistently, and maintaining body temperature in an open crib. There also needs to be a stretch of days without any apnea or heart rate drops.
One step many parents don’t expect is the car seat test. Within the week before discharge, your baby will sit in a car seat (either yours or a hospital model) while being monitored for at least 20 minutes. The team watches for any pauses in breathing, heart rate drops below 80 beats per minute, or dips in oxygen levels below 90%. If your baby passes, you’re cleared. If not, the test is repeated after more time, or the team may recommend a car bed for travel instead.
You’ll also receive hands-on training in infant CPR, safe sleep positioning, and how to feed your baby, whether by breast, bottle, or a combination. Many NICUs encourage “rooming in” for a night before discharge so you can care for your baby independently with staff nearby.
A Realistic Week-by-Week Picture
During the first week, your 33-weeker is likely working on breathing stability and may be receiving tube feedings. Jaundice treatment, if needed, usually happens in this window. You’ll be encouraged to do skin-to-skin contact (kangaroo care) as much as possible, which has measurable benefits for temperature regulation, breathing patterns, and bonding.
By the second week, many 33-weekers are off any breathing support and beginning to take some feedings by mouth. The incubator-to-crib transition often happens around this time. Apnea episodes, if they were occurring, may be tapering off.
During weeks three and four, the focus shifts almost entirely to feeding. Your baby is building the stamina to finish full feeds consistently and gaining weight. Once the feeding milestone is met, discharge planning moves fast. Many families take their 33-weeker home between 35 and 37 weeks of corrected gestational age.
The NICU stay for a 33-weeker can feel long, but it’s one of the shorter stays in the unit. Knowing what milestones to watch for can help the days feel less open-ended, even when you can’t pin down an exact date.