Babies shiver, shake, or jitter for reasons that have nothing to do with being cold. The most common explanation is simple: your baby’s nervous system is still immature. In the first days and weeks of life, a baby’s brain is still learning how to control small muscles, which can produce brief shaking, shivering, or jittery movements that come and go throughout the day. These movements are a normal part of adjusting to life outside the womb and typically fade on their own.
That said, not all shivering-like movements are the same. Some are completely harmless, some signal a temporary physical need like low blood sugar, and a small number warrant prompt medical attention. Here’s how to tell the difference.
Immature Nervous System: The Most Common Cause
Newborns arrive with a nervous system that’s still under construction. The pathways between the brain and the muscles aren’t fully insulated yet, so signals can “leak” into involuntary movements. You might notice quick, rhythmic trembling in your baby’s legs, arms, or chin, especially when they’re crying, startled, or transitioning between sleep and wakefulness. These fine tremors are extremely common in the first few weeks and tend to decrease as the nervous system matures over the first two to three months.
A good way to test whether a tremor is this benign type: gently hold the shaking limb. If the movement stops when you apply light pressure, it’s likely just normal newborn jitteriness. Movements that continue despite being held, or that involve rhythmic patterns you can’t interrupt, are worth mentioning to your pediatrician.
Shuddering Attacks
Some babies develop brief, dramatic episodes that look like a full-body shiver or shudder. These are called shuddering attacks, and they’re benign. They typically start around four to six months of age and involve a rapid tremor of the head, sometimes with the arms pulling inward and the knees drawing together. Each episode lasts only a few seconds.
Shuddering attacks can happen many times a day. Some children experience over 100 episodes daily. They tend to be triggered by excitement, stimulating play, eating, or breastfeeding. One Turkish study of 19 children found that nearly 80% of cases began during teething, suggesting that the discomfort or sensory stimulation of new teeth may act as a trigger. These attacks disappear on their own, usually by age four, and they don’t affect development or indicate epilepsy.
The key features that separate shuddering attacks from something more concerning: the child stays fully conscious, the episodes are very brief (seconds, not minutes), and they never happen during sleep.
Sleep Myoclonus
If your baby’s shivering only happens while they’re asleep, you may be seeing benign sleep myoclonus. This condition involves jerking or twitching movements of the arms, legs, and trunk during sleep. The face is spared. Episodes tend to come in clusters during quiet sleep and stop immediately when the baby wakes up.
Sleep myoclonus typically appears within the first two weeks of life, often as early as the first few days. It resolves on its own, usually by two to four months, and almost always by six months. In one study, the median age of resolution was just two months. Interestingly, the jerking can sometimes be triggered or worsened by rocking the baby or by repetitive sounds.
This condition requires no treatment and has no effect on neurological development. The brain wave patterns during these episodes are completely normal. What makes it easy to identify: the movements vanish the moment your baby wakes up, and there’s no eye rolling, color change, or change in breathing.
The Moro (Startle) Reflex
Sometimes what looks like a shiver is actually the Moro reflex. This is a hardwired startle response: when your baby is startled by a sudden noise, movement, or even their own cry, they throw their head back, fling their arms and legs outward, and then pull them back in. It can be accompanied by crying. Parents sometimes describe this as a sudden full-body trembling.
The Moro reflex is present from birth and fades by about five to six months. It’s completely normal and is actually something pediatricians check for during well-baby visits as a sign of healthy neurological function.
Low Blood Sugar and Other Metabolic Causes
Shivering or trembling in a newborn can occasionally signal low blood sugar (hypoglycemia). When a baby’s glucose drops below a safe level, their body may respond with shakiness, sweating, or jitteriness. This is more common in premature babies, babies who are large or small for their gestational age, and babies born to mothers with diabetes.
Low blood sugar episodes are most likely in the first 24 to 48 hours of life and are routinely screened for in the hospital for at-risk newborns. If your baby is feeding well, gaining weight, and alert during wake periods, low blood sugar is unlikely to be the cause of occasional shivering. But if the trembling is accompanied by poor feeding, unusual sleepiness, or a weak cry, it’s worth getting a check.
Low calcium levels can produce similar symptoms. Like hypoglycemia, this is more common in premature infants and is typically identified through blood work if a doctor suspects it.
How to Check Your Baby’s Temperature
Before assuming your baby isn’t cold, it helps to confirm with a thermometer rather than relying on how their hands or feet feel. Babies naturally have cool hands and feet due to immature circulation, so those aren’t reliable indicators of core body temperature.
A rectal thermometer gives the most accurate reading for infants. A normal temperature is below 100.4°F (38°C) rectally. Ear and temporal artery thermometers share the same threshold. An armpit reading above 99°F (37.2°C) is considered elevated. If your baby is shivering and has a fever, the shivering may actually be a febrile response, which is a different situation from the benign causes described above.
Signs That Need Prompt Attention
Most shivering-like movements in babies are harmless. But a specific type of movement called infantile spasms is a medical emergency that can look deceptively subtle. Infantile spasms involve sudden stiffening of the body, arching of the back, or brief bending of the arms, legs, or head forward. You might also notice repeated head nodding, the head pulling to one side, eyes rolling upward, or chin twitching. These movements typically happen in clusters, with five to ten seconds between each spasm.
Infantile spasms are considered urgent because even a few days or weeks without treatment can harm brain development. They usually appear between three and twelve months of age. If you notice even one or two episodes that match this pattern, contact your child’s doctor immediately.
Other reasons to seek evaluation promptly: trembling that you cannot stop by gently holding the limb, shaking episodes that last longer than 20 to 30 seconds, movements accompanied by eye deviation or changes in skin color, and any episode where your baby seems unresponsive or stops breathing briefly during the shaking.