If you've spent any time beside your baby in the NICU, you've probably learned to recognize the sound of the monitor alarms.

You look up and see the oxygen saturation number dropping: 92... 88... 84...

And even when the nurses around you seem calm, it can be frightening to watch.

These drops in oxygen saturation are often called desaturations, or "desats." They're common in premature and medically fragile babies, but that doesn't mean every desaturation has the same cause—or that you shouldn't ask questions about what you're seeing.

Understanding why desats happen can make those alarms a little less mysterious.

What Is a Desaturation?

The pulse oximeter—the small sensor usually wrapped around your baby's hand or foot—estimates how much oxygen is being carried in the blood.

You'll see that measurement displayed on the bedside monitor as SpO₂, or oxygen saturation.

A desaturation is a drop in your baby's oxygen saturation. In the NICU, the team considers how far the saturation falls, how long it lasts, your baby's prescribed target range, and what else is happening clinically.

One important thing for parents to know is that there isn't one perfect oxygen number for every NICU baby.

Your baby's desired range may depend on their gestational age, medical condition, respiratory support, and other factors. That's why the alarm limits you see at your baby's bedside may be different from those of the baby in the next room.

Why Do Premature Babies Desat?

Premature babies are still developing many of the systems that help full-term babies maintain steady breathing and oxygen levels.

Their lungs may be immature, but so is the part of the brain responsible for controlling breathing.

Sometimes a premature baby simply pauses or breathes too shallowly for a short period. Oxygen levels may fall, and the heart rate may sometimes decrease as well.

You may hear the NICU staff refer to these events as apnea, bradycardia and desaturation—or A/B/D events.

But immature breathing isn't the only reason a baby may desaturate.

Common Reasons You May See the Oxygen Level Drop

Apnea of prematurity

Very premature babies may temporarily stop breathing because their respiratory control system isn't fully mature.

When breathing pauses long enough, oxygen saturation can fall. Sometimes the baby's heart rate falls too.

As premature babies mature, apnea of prematurity generally becomes less frequent and eventually resolves.

Feeding

Feeding is surprisingly complicated.

A baby has to coordinate sucking, swallowing and breathing—and premature babies may still be learning how to put all three together.

You may notice your baby's oxygen saturation fall during a bottle or breastfeeding session, particularly when your baby becomes tired.

This is one reason NICU nurses and feeding specialists pay such close attention to pacing, positioning, feeding cues and your baby's overall tolerance.

Positioning or movement

Sometimes the monitor number changes because your baby moved, kicked, cried or disturbed the pulse-oximeter sensor.

In those situations, the monitor may not be getting a reliable signal.

NICU staff don't evaluate only the number on the screen. They also look at your baby.

Is your baby breathing?

What color is your baby?

What does the heart rate show?

Is the pulse-ox signal reliable?

The monitor provides important information, but it is only one part of the assessment.

Respiratory illness or immature lungs

Babies who need oxygen, CPAP, a ventilator or other respiratory support may experience changes in oxygen saturation related to their underlying lung condition.

The NICU team watches patterns over time and may adjust respiratory support based on the baby's overall clinical picture.

Secretions and other factors

There can be many other reasons for oxygen saturation changes.

Sometimes an event has an obvious explanation. Other times the team looks at the pattern—when the episodes happen, how long they last, what the baby was doing beforehand and whether anything else changed at the same time.

Why Does the Nurse Sometimes Wait Before Doing Anything?

This can be one of the hardest things for parents to understand.

The alarm is sounding.

The oxygen number is falling.

And the nurse isn't immediately rushing toward the bed.

Often, that's because the nurse is assessing the situation before intervening.

Some premature babies briefly desaturate and recover on their own. Depending on the baby and the circumstances, the nurse may watch for a few seconds to see whether the baby self-recovers.

Other events may require stimulation, repositioning, airway or respiratory support, or another intervention based on the cause.

The appropriate response depends on your baby, the cause of the event and how your baby is responding.

A calm nurse doesn't necessarily mean the alarm is being ignored. It may mean the nurse understands your baby's usual pattern and is watching closely.

When Should Parents Ask About Desaturations?

Any time you're worried.

You don't need to understand the monitor well enough to decide whether something is medically important before asking a question.

Try asking:

"Is this type of desaturation typical for my baby?"
"Do you know what seems to trigger these episodes?"
"Is my baby recovering without help?"
"Are the episodes becoming more or less frequent?"
"Do they happen more often during feeds or sleep?"
"What would make you concerned about an episode?"

Those questions can help you understand your baby's individual pattern, which is much more useful than comparing monitor numbers with another NICU baby.

One Thing I Want NICU Parents to Remember

Monitors are designed to alert the medical team to changes.

That means they alarm frequently—and not every alarm represents an emergency.

Over time, you'll probably start recognizing some of the numbers and alarm sounds yourself. That's completely normal.

But you don't have to become your baby's monitor technician.

Your most important job is still to be your baby's parent.

Ask questions. Learn what the team is watching. Participate in your baby's care when you can.

And when the monitor starts beeping and you're frightened, it's always okay to ask the nurse:

"Can you tell me what's happening?"

New to the NICU?

The first days in the NICU can feel like learning an entirely new language while you're also trying to process everything happening with your baby.

The Bright Sprout 7-Day NICU Survival Guide was created to help make those first days a little more manageable, with practical information and gentle support delivered one day at a time.

Get the free 7-Day NICU Sur vival Guide →

This information is intended for general education and support and does not replace medical advice from your baby's healthcare team. Every baby's medical needs and recommended oxygen targets are different.

Sources and Clinical References

Eichenwald EC; American Academy of Pediatrics Committee on Fetus and Newborn. Apnea of Prematurity. Pediatrics. 2016;137(1):e20153757.
Martin RJ. Control of Breathing and Apnea of Prematurity. NeoReviews. 2018;19(4):e224–e234.
Cummings JJ, Polin RA; American Academy of Pediatrics Committee on Fetus and Newborn. Oxygen Targeting in Extremely Low Birth Weight Infants. Pediatrics. 2016;138(2):e20161576.
Di Fiore JM, Martin RJ, Gauda EB. Intermittent Hypoxemia in Preterm Infants. Clinics in Perinatology / neonatal review literature. 2019.
Slocum C, Arko M, Di Fiore J, et al. Apnea, Bradycardia and Desaturation in Preterm Infants Before and After Feeding. Journal of Perinatology. 2009;29:209–212.

A note about this resource: Bright Sprout provides educational and supportive information for NICU families. This content is not intended to replace medical advice, diagnosis, or treatment from your baby’s healthcare team. Every baby and NICU journey is different. If you have questions or concerns about your baby’s health or care, please talk with your NICU team.

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