Why Is My Newborn So Squirmy in Their Sleep? (It's Called Active Sleep)

You tiptoe over to the bassinet at 4 a.m., convinced your baby is about to wake up. The grunting has started again — those little squeaks and leg kicks that sound like your newborn is wrestling an invisible opponent. You stand there, hand hovering, wondering if you should pick them up or let them be. Here's what most new parents don't realize: your baby is probably still asleep. What you're witnessing is active sleep, and it's one of the most misunderstood parts of early parenthood. This isn't a sign that something is wrong — it's actually a normal, healthy part of how newborns sleep, even though it can look and sound pretty dramatic. In this post, we'll walk through exactly what active sleep is, why it happens so often in newborns, what it looks and sounds like, and how to tell when your baby truly needs you versus when they're just moving through a normal sleep cycle.

What Is Active Sleep in Newborns — And Why Does It Happen So Much?

Active sleep is the newborn version of REM sleep — the lighter, dream-rich sleep stage that adults experience too. But here's the key difference: while adults spend only about 20–25% of their sleep time in REM, newborns spend roughly 50% of total sleep time in active sleep[1], according to landmark research by Roffwarg, Muzio, and Dement published in Science back in 1966. That one statistic explains so much of what you're seeing. Your baby isn't "bad at sleeping." They're just spending half their sleep time in a state that naturally includes more movement, more noise, and more visible activity than the deep, still sleep you might expect.

The other half of your baby's sleep is called quiet sleep — the deeper, calmer phase where breathing is more regular, the body is still, and your baby looks genuinely peaceful. According to HealthyChildren.org, babies in active sleep may twitch, jerk, have rapid eye movements under closed lids, make small sounds, and even grimace or smile. All of this is normal and not a sign of discomfort or poor sleep quality.

Newborn sleep cycles are also much shorter than adult cycles — about 50 to 60 minutes, as noted in Grigg-Damberger's review of infant sleep development[2]. This means your baby moves between active and quiet sleep more frequently than you do, which is why so many parents say, "My baby gets noisy every hour." That hourly pattern isn't random. It's your baby transitioning between sleep states, and because newborn sleep is still a little clunky (as we like to say at The Peaceful Sleeper), those transitions can be loud, obvious, and surprisingly dramatic.

A really common pattern: baby sleeps relatively quietly for the first stretch of the night, then becomes much noisier from about 3 to 6 a.m. — grunting, leg-lifting, squirming — all while still mostly asleep. This isn't a sign that something changed. It's just that sleep pressure is lower by morning, so active sleep phases are more noticeable. You're hearing what was happening all along, but now it's more obvious because your baby isn't as deeply tired as they were at bedtime.

One more thing worth knowing: back sleeping can make all of this look and sound more dramatic. When babies sleep on their backs (which is the safest position, as confirmed by the American Academy of Pediatrics' safe sleep guidelines from Moon et al. 2022[3]), every grunt, squirm, and leg kick is more visible and audible. I know it can look uncomfortable — but back is still best, and what you're seeing is normal newborn sleep, not a baby who's struggling.

What Active Sleep Actually Looks and Sounds Like

So what does active sleep really look like when you're standing over the bassinet at 2 a.m.? Here's the full picture: squirming, brief body jerks, facial grimaces, fluttering eyelids, little squeaks, grunts, irregular breathing, tiny cries, leg lifting, and sometimes even eyes that seem partly open for a moment. These behaviors often happen together — not one at a time, but as a cluster. That's the part that can be so unnerving. It's not just one grunt. It's a grunt plus a leg kick plus a grimace plus a little squeak, all in the span of ten seconds. But here's what matters: these signs are a normal sleep-state package, not proof that your baby is distressed.

Research by Curzi-Dascalova and Plouin on neonatal sleep organization[4] helps explain why active sleep can genuinely look like "struggling" to a worried parent. During active sleep, breathing is more irregular, facial activity is more obvious, and body movement is more frequent compared to quiet sleep. Your baby's chest might rise and fall unevenly. Their face might scrunch up like they're concentrating hard on something. Their arms might fling out suddenly, or their legs might pull up toward their belly and then slam back down. All of this is happening because the brain is active, the body is less inhibited, and your baby is in a lighter sleep state. It doesn't mean they're in pain — it just means they're in active sleep, and active sleep is busy.

One of the most fascinating insights comes from developmental neuroscience work by Mark S. Blumberg and his colleagues. In a 2014 study published in Current Biology by Tiriac, Del Rio-Bermudez, and Blumberg[5], researchers found that sleep twitches in newborns are structured and may actually help build sensorimotor maps in the developing brain. In practical terms, this means some of the squirming you're seeing may be part of your baby's brain-body "calibration" work — a kind of internal rehearsal that helps them learn how their limbs move and where their body is in space. It's not a sign of bad sleep. It's developmental work happening during sleep.

Here's a pattern that shows up constantly in parent communities: babies who seem "peaceful on me but wild in the bassinet." This creates so much worry — parents start to think their baby has a difficult temperament, that the bassinet is the problem, or that they're doing something wrong. But researcher Helen Ball, who leads the BASIS (Baby Sleep Info Source) project, offers a much more helpful explanation. Proximity changes how infant sleep is perceived. When your baby is asleep on your chest, contact sleep masks small motions — you absorb the little twitches and grunts, and your own breathing and heartbeat create a sensory buffer. But in a bassinet, every grunt gets amplified and every leg kick echoes against the mattress. The baby hasn't changed. Your ability to observe them has.

One last nuance worth mentioning: swaddling may reduce flailing arms, but it won't necessarily stop all movement. Parents sometimes swaddle expecting total stillness, then find their baby becomes more torso-twisty or grunty because the movement gets redirected — arms are contained, so the energy goes into the legs and core instead. Swaddling is still a helpful tool for many babies, but it's not a magic solution that makes active sleep look perfectly still. Your baby is still going to move and grunt, swaddled or not.

How to Respond Without Accidentally Waking Your Baby

Here's the core principle from The Peaceful Sleeper's approach: newborn sleep is clunky, and many babies need a little time to resettle on their own. When you hear grunting or squirming at 3 a.m., your instinct is to rush in immediately. But if it's not clearly feeding time and your baby is still mostly asleep, the most helpful thing you can do is pause. Observe first, then decide.

This matters more than you might think. A recurring pattern in parent communities: first-time parents mistake active sleep for waking, then feed, rock, or pick the baby up too soon — and accidentally create a full wake-up. One parent described it perfectly: "I thought she was waking up every hour because she'd grunt and kick. Turns out I was waking her up every hour by picking her up." Another wrote, "Once I started waiting 30 seconds, I realized he was still asleep half the time and would settle on his own."

Wait and observe if:

- Your baby's eyes are still closed (or only briefly flutter open and close again)

- The noises rise and fall rather than escalating steadily

- The squirming happens without sustained crying

- The movements settle on their own after a few seconds or a minute

- It hasn't been long since the last feed

Go ahead and intervene if:

- It's actually time to eat based on your baby's typical feeding rhythm

- Your baby has escalated into being clearly awake — eyes open, looking around, crying that builds rather than fades

- The fussing persists beyond a brief resettling window (always feed on demand)

Research by Anders, Sadeh, and Appareddy in 1995[6] found that newborn sleep includes frequent state transitions and mixed states. Your baby isn't just "asleep" or "awake" — they move through partial arousals, brief waking moments, and shifts between active and quiet sleep throughout the night. The squirmy, noisy moments you hear are often transitions rather than true awakenings. When you rush in during a transition, you risk turning a moment that would have resolved on its own into a full wake-up that now requires soothing, feeding, or rocking to get your baby back to sleep.

When It's Not Just Active Sleep

Most squirmy newborn sleep is exactly that: normal active sleep. But I also want to give you a clear framework for when something else might be going on, because the last thing you need is false reassurance when your gut is telling you something feels off.

Active sleep is far more likely when symptoms happen mainly during sleep with eyes closed, the baby settles when left alone, weight gain stays on track, and the behavior is concentrated overnight rather than after every single feed while awake. The classic picture: "He's noisy and squirmy from 3 to 6 a.m., but during the day when he's awake and alert, he seems totally fine."

Now contrast that with signs that point toward reflux, feeding issues, or discomfort beyond normal sleep behavior:

• Ongoing discomfort while fully awake — your baby seems uncomfortable even when alert, not just during sleep transitions

• Frequent back-arching after feeds — especially if it happens consistently

• Refusing to lie flat when awake, too — if your baby only seems comfortable upright even during awake time

• Persistent sour-smelling spit-up — not just the occasional posset, but frequent, strong-smelling reflux

• Blood or mucus in stool — this can signal a milk protein sensitivity or other feeding issue

• Poor weight gain — if your pediatrician has raised concerns about growth

• Crying that does not improve when the baby is picked up — true discomfort often persists even with contact and soothing

The key difference: active sleep noises and movements happen during sleep and often resolve on their own. Reflux or feeding discomfort shows up while awake, persists even when you hold your baby, and tends to follow feeds rather than being concentrated in the second half of the night.

One more important note: persistent noisy breathing while awake, color change (blue or pale), chest retractions (skin pulling in around the ribs), pauses in breathing, wheezing, or stridor (a high-pitched sound when breathing in) deserve medical evaluation. HealthyChildren.org's guidance on laryngomalacia and stridor can help you understand what concerning breathing sounds actually sound like.

And a rare but important distinction: infantile spasms are most common just after a baby wakes and are not the same as the jerky movements or startle reflexes you see during active sleep. Infantile spasms are repetitive, clustered movements — often described as sudden stiffening or jackknife-like motions — that happen when your baby is waking up or fully awake. If you see repetitive, concerning movements during waking, trust your instinct and talk to your pediatrician.

Here's the reassurance I want you to hold onto: most squirmy newborn sleep is normal. You are not supposed to know every cue instantly. Being a "good enough" parent means staying observant, not perfect. You're learning your baby, and your baby is learning how to sleep outside the womb — and that takes time for both of you. If your baby was born preterm, research by Curzi-Dascalova and Plouin reminds us that former preterm infants may not follow the exact same timeline as term newborns. Corrected age and individual context matter, so give yourself grace. You're doing better than you think.

Sources

1. Roffwarg, H. P., Muzio, J. N., & Dement, W. C. (1966). Ontogenetic development of the human sleep-dream cycle.

2. Grigg-Damberger, M. M. (2006). Development of sleep/wake behaviors in infants.

3. Moon, R. Y., et al. (2022). Safe sleep guidelines from the American Academy of Pediatrics.

4. Curzi-Dascalova, L., & Plouin, P. (1980s). Neonatal sleep organization research.

5. Tiriac, A., Del Rio-Bermudez, C., & Blumberg, M. S. (2014). Self-generated movements with sleep twitches in newborns.

6. Anders, T. F., Sadeh, A., & Appareddy, V. (1995). Normal sleep patterns in neonates and infants.