Understanding 'As and Bs': The Biology and Symptoms of Apnea of Prematurity

It is one of the most stressful experiences for any NICU parent: sitting by your baby’s bedside, only to be startled by the piercing sound of a monitor alarm. These alarms usually signal what the medical team calls ABD events—short for Apnea, Bradycardia, and Desaturation ^[1][2]. While these sounds are frightening, they are also a reflection of your baby’s journey toward maturity. Understanding the biology behind these “spells” can help you navigate the noise with a bit more clarity.

What is Apnea of Prematurity?

In the NICU, apnea is defined as a pause in breathing that lasts for 20 seconds or longer ^[3]. A pause can also be considered apnea if it is shorter than 20 seconds but is accompanied by a drop in heart rate or oxygen levels ^[2].

This condition, known as Apnea of Prematurity (AOP), is a common developmental stage rather than a permanent disease ^[3][4]. It occurs because the brainstem—the part of the brain that controls automatic functions like breathing—is not yet fully developed ^[5][4].

The ‘As and Bs’ (and Ds)

When the monitor alarms, the team is looking for three specific signs:

• Apnea (The ‘A’): The baby stops breathing for at least 20 seconds ^[3].
• Bradycardia (The ‘B’): A drop in heart rate below the normal range for a newborn (often defined as below 80 or 100 beats per minute, depending on the hospital’s protocol) ^[2][6].
• Desaturation (The ‘D’): A drop in the level of oxygen in the blood, often called a “desat” ^[2].

Why Does This Happen?

The primary cause of these events is brainstem immaturity ^[7]. In a full-term baby, the brainstem sends constant, rhythmic signals to the breathing muscles. In a premature baby, these neurological signaling pathways are still growing and can occasionally “misfire” or pause ^[8].

Think of it like a new computer’s operating system that is still installing—sometimes it “glitches” and needs a second to reboot ^[9]. As the brainstem matures and the regions responsible for respiratory drive grow, these glitches naturally become less frequent and eventually stop ^[9][3].

What to Do During an Alarm

As a parent, your first instinct when an alarm sounds is panic. You might wonder, “Do I stimulate my baby? Do I wait for the nurse?” Here is a general guide:

1. Look at your baby, not the monitor: Is your baby’s chest moving? What is their color? Sometimes monitors give “false alarms” because the baby moved ^[10].
2. Wait for the nurse to lead: Often, premature babies just need a few seconds to “self-recover.” Over-stimulating them too quickly can actually disrupt their learning process ^[11].
3. Learn from the team: Ask your nurse to show you when and how to provide gentle tactile stimulation (like lightly rubbing their back) if the baby doesn’t self-recover.

Managing the ‘Spells’

The goal of the NICU team is to support your baby while their brain matures. The team uses Standard of Care Treatments like continuous monitoring, caffeine therapy (which gently stimulates the brain’s breathing center), and respiratory support tools like CPAP ^[12][13].

These events almost always resolve on their own as the baby reaches a corrected age of 36 to 40 weeks ^[3][14]. Most NICUs require a baby to clear a Discharge Countdown before they are considered ready to go home ^[15]. If your baby’s spells seem unusually frequent, the team will ensure they are Ruling Out Other Causes like infections. Most importantly, research shows a very positive Long-Term Outlook for these babies.