Newborns move so much during sleep because they spend roughly half their total sleep time in a light, active phase called REM sleep. During this phase, their bodies twitch, jerk, squirm, and flutter their eyelids, all while still fully asleep. For adults, REM makes up only about 20–25% of sleep, so the sheer amount of movement a newborn produces can look alarming. It’s not. It’s one of the most normal things a healthy baby does.
Active Sleep Takes Up Half the Night
Newborns sleep around 16 hours a day, and about 8 of those hours are spent in REM sleep. During REM, a baby’s brain is intensely active, forming neural connections at a pace it will never match again. The body reflects that activity: you’ll see eye movements behind closed lids, facial grimaces, mouth sucking motions, arm and leg twitches, and irregular breathing. In between REM cycles, babies enter deeper non-REM stages where they become very still and quiet. The contrast can be striking. One minute your baby looks like they’re running a marathon in their bassinet, and a few minutes later they’re completely motionless.
Because newborns cycle between light and deep sleep much faster than adults (roughly every 20–50 minutes), you’ll see these bursts of movement frequently throughout the night. As your baby’s brain matures over the first year, the proportion of REM sleep gradually decreases and sleep cycles lengthen, which means the constant wiggling settles down on its own.
The Moro Reflex and Sudden Startles
If your baby suddenly flings their arms out, arches their back, and sometimes cries, that’s the Moro reflex. It’s triggered when a baby’s balance system detects the sensation of falling or is startled by a sudden noise, light change, or even their own twitching during light sleep. Laying a baby down onto their back is one of the most common triggers, which is why you might notice it right at the start of a nap.
The Moro reflex is present from birth and typically fades by 5 to 6 months. If your baby still shows the full reflex past 6 months, it’s worth mentioning to your pediatrician. Until then, it’s a normal part of neurological development, just a particularly dramatic one at 3 a.m.
Digestion Doesn’t Pause During Sleep
A lot of the grunting, groaning, and squirming you hear and see has nothing to do with sleep stages. It’s your baby’s digestive system at work. Newborns are still learning to coordinate the muscles needed to burp, pass gas, and push out stool. That takes real effort, and digestion keeps going while they sleep. The result is a baby who sounds like a tiny weightlifter: straining, squirming, making rumbling belly noises, and sometimes turning red in the face, all without waking up. This is sometimes called “grunting baby syndrome,” and it resolves as your baby’s abdominal muscles and coordination mature over the first few months.
How to Tell if Your Baby Is Actually Awake
One of the trickiest parts of newborn sleep is figuring out whether all that movement means your baby needs you or is still asleep. Picking up a baby during active sleep can accidentally wake them, cutting a sleep cycle short. A few cues help you tell the difference.
During light sleep, a baby’s eyes stay closed (though you may see them moving underneath the lids), their movements are jerky and random, and they may make brief fussing sounds that stop on their own. They might even smile or make sucking motions. All of this is normal REM activity.
A baby who is actually waking up will go through a transitional phase: their eyelids droop and eyes roll, they stretch and yawn, and their arm and leg movements become more purposeful. Once fully awake, they’ll either be calm and alert with open eyes, actively moving their face and body, or crying. If your baby is in the jerky, eyes-closed stage, give it a minute or two before intervening. They’ll often settle back into deeper sleep on their own.
Normal Twitches vs. Something More Serious
Rhythmic jerking during sleep can occasionally look concerning, and parents sometimes wonder whether they’re seeing a seizure. There is a well-documented condition called benign sleep myoclonus, where a baby has repetitive, rhythmic jerks while drowsy or asleep. The key feature: the movements stop when the baby is woken up. Brain activity during these episodes is completely normal. The condition can appear from the first day of life and typically resolves on its own by age 3, often much earlier.
This pattern is frequently misdiagnosed as epilepsy, leading to unnecessary testing and medication that can actually make things worse by increasing drowsiness and triggering more episodes. If you notice rhythmic jerking that concerns you, the simplest test is waking your baby. If the movements stop immediately, that’s a reassuring sign. Movements that continue when the baby is fully awake, involve only one side of the body, or come with unusual eye movements or changes in skin color are worth a call to your pediatrician.
Keeping an Active Sleeper Safe
Because newborns move so much, their sleep environment matters. The basics: always place your baby on their back on a firm, flat surface that doesn’t indent under their weight. Use a crib, bassinet, or play yard that meets current safety standards, with only a fitted sheet inside. No blankets, pillows, stuffed animals, or bumpers. Any surface inclined more than 10 degrees is not safe for sleep, and if your baby falls asleep in a car seat, swing, or carrier, move them to a flat surface as soon as you can.
Offering a pacifier at sleep time can reduce the risk of SIDS, even if it falls out after your baby is asleep. If you’re breastfeeding, wait until feeding is well established before introducing one.
When to Transition Out of a Swaddle
Swaddling can help dampen the Moro reflex and keep a baby from startling themselves awake, but it has a firm expiration date. You need to stop swaddling once your baby shows any signs of rolling from back to front, attempts to push up, or regularly breaks free from the wrap. A swaddled baby who rolls onto their stomach cannot use their arms to reposition, which creates a suffocation risk. Most babies hit this milestone somewhere between 2 and 4 months. Transitional sleep sacks that leave the arms free are a common next step.
When the Movement Settles Down
The peak of nighttime movement is in the first 2 to 3 months, when REM sleep dominance, the Moro reflex, and digestive immaturity all overlap. By around 3 to 4 months, sleep cycles begin to organize into longer stretches of deeper sleep. The Moro reflex fades by 5 to 6 months. Digestive coordination improves steadily over the same window. By 6 months, most babies are noticeably calmer sleepers, though brief twitches and position changes during lighter sleep stages remain a normal part of sleep at any age.