Babies move a lot at night because they spend roughly half their total sleep time in a light, active sleep phase that causes twitching, squirming, and flailing. This is completely normal and tied to how infant brains develop. For most babies, nighttime movement gradually decreases over the first six to nine months as their sleep patterns mature and primitive reflexes fade.
Active Sleep Takes Up Half the Night
Adults cycle through sleep stages in a predictable pattern, spending only about 20 to 25 percent of the night in REM (the lightest, most active phase). Newborns, by contrast, spend about 50 percent of their 16 daily hours of sleep in REM. During this phase, babies twitch their fingers and toes, jerk their limbs, grimace, make sucking motions, flutter their eyelids, and sometimes cry out briefly before settling again. It can look alarming, but all that movement reflects a brain that’s rapidly building neural connections.
Because babies enter REM sleep almost immediately after falling asleep (adults take about 90 minutes to get there), you’re more likely to notice the movement right after you put your baby down. And because their sleep cycles are shorter, only about 50 to 60 minutes compared to 90 minutes in adults, they pass through this active phase more frequently throughout the night. Each transition between cycles is another window for visible movement and brief waking.
Their Internal Clock Isn’t Set Yet
Newborns are born without a functioning circadian rhythm. They don’t produce melatonin at birth, and their cortisol rhythm, which helps regulate the sleep-wake cycle, can take anywhere from two weeks to nine months to fully establish. Without these hormonal signals telling the brain “it’s nighttime, stay deeply asleep,” babies drift in and out of light sleep more easily, and that means more movement.
Consolidated nighttime sleep starts to emerge around 15 weeks, when wake and sleep episodes become more distinct. By six to nine months, most infants can manage at least a six-hour stretch of uninterrupted sleep. One interesting finding: an infant exposed exclusively to natural light for the first six months developed a measurable sleep-wake rhythm by about day 45 and had sleep onset aligned with sunset by day 60, suggesting that consistent light-dark cues help the internal clock mature faster. Keeping daytime bright and active while making nighttime dark and quiet can support this process.
The Startle Reflex Plays a Role
The Moro reflex, commonly called the startle reflex, is a primitive response present from birth. When a baby senses a sudden change in position or support, their arms fling outward with fingers spread, then quickly pull back in, often followed by a cry. This reflex fires easily during light sleep, when a small noise, a vibration, or even the baby’s own movement can trigger it. The result is a dramatic jerk that may wake the baby or simply add to the general nighttime commotion.
The Moro reflex typically disappears by six months. Until then, swaddling can help suppress it, but only while your baby isn’t yet showing signs of rolling. Once a baby starts attempting to roll, usually around three to four months, swaddling should stop because a swaddled baby who rolls face-down can’t push up to clear their airway.
Room Temperature and Comfort
Babies who are too warm tend to be restless. A room temperature between 68 and 72 degrees Fahrenheit (20 to 22 degrees Celsius) is the comfortable range for most infants. Anything above 72 degrees may cause overheating, which increases both restlessness and the risk of sleep-related complications. Dress your baby in one layer more than you’d wear comfortably in the same room, and skip blankets entirely in the crib. If your baby’s chest feels warm and dry to the touch, they’re likely at the right temperature. Sweaty skin or a flushed face suggests the room is too warm.
Other environmental triggers that increase nighttime movement include hunger (younger babies need frequent feeds), gas or digestive discomfort, teething pain, and growth spurts. These tend to produce fussier, more wakeful movement rather than the rhythmic twitching of active sleep.
When Movement Looks Concerning
Most nighttime movement is harmless, but there’s one pattern worth knowing about. Benign sleep myoclonus causes rhythmic, jerky movements during sleep that can look startling, sometimes affecting just one side of the body. The defining feature is simple: the movements stop when the baby wakes up. If you gently rouse your baby by changing a diaper or lightly squeezing an arm, and the jerking stops, it’s almost certainly benign. In a study of 15 infants with this condition, none later developed epilepsy.
The movements to watch for are ones that don’t stop when the baby wakes. Infantile spasms, a rare but serious seizure type, typically involve clusters of sudden, brief stiffening episodes where the arms and legs pull inward. They can happen during wakefulness, not just sleep. If your baby has repetitive stiffening episodes that persist when they’re awake, or if they seem to be losing developmental skills they previously had, that warrants prompt evaluation.
Keeping the Crib Safe for Active Sleepers
As babies grow and their nighttime movement becomes more purposeful, rolling, scooting, and eventually pulling up, the sleep environment matters more. The crib should contain nothing but a firm mattress and a fitted sheet. No bumpers, pillows, stuffed animals, or loose blankets. Once your baby can roll both directions (from back to stomach and stomach to back), you can let them settle into whatever position they choose. There’s no need to keep flipping them onto their backs all night.
Babies who start rolling onto their stomachs during sleep often seem to sleep more soundly in that position, which can actually reduce some of the restless movement that brought you to this article in the first place. The key is making sure the mattress surface is firm and clear so that any position they end up in is a safe one.