Seeing your newborn’s leg shake can be startling. Most of the time, this movement is a normal part of infant development. Newborns have immature nervous systems, which often causes brief, rhythmic tremors in the arms and legs.
These shakes usually last a few seconds and stop on their own. They happen when the baby is crying, startled, or in light sleep. In most cases, this is not a sign of a problem. However, there are specific times when leg shaking points to a medical issue that needs attention.
Why Do Newborns Shake Their Legs?
A newborn’s brain and spinal cord are still developing. The nerve pathways that control movement are not fully insulated yet. This means signals can fire more easily and spread to nearby muscles, causing visible tremors.
These tremors are common and are called “jitteriness.” They are distinct from seizures, which involve a different pattern of movement. Jitteriness is a rapid, back-and-forth shaking motion. It stops when you gently hold the limb still.
Several normal situations trigger this response. Crying and the Moro reflex (the startle response) are the most common. A sudden noise, a change in temperature, or being moved quickly can all cause a brief leg shake. Feeding also plays a role. Low blood sugar, even at a normal level for a newborn, can cause temporary tremors that resolve after a good feed.
Jitteriness vs. Seizures: What Is the Difference?
Distinguishing a benign tremor from a seizure is the most important step. The movement patterns are different, and knowing the difference can reduce panic.
Jitteriness is a rapid, rhythmic shaking that looks like a vibration. It is symmetrical, meaning both legs often shake the same way. The key feature is that the shaking stops when you hold the leg or soothe the baby. It also stops when the baby is repositioned.
Seizures in newborns look different from seizures in older children or adults. They are often subtle. Look for these signs:
- Repeated jerking that does not stop when you hold the limb
- Movements that are not rhythmic, like bicycling motions of the legs
- Eye rolling, blinking, or staring that does not respond to your voice
- Stiffening of the whole body followed by limpness
- Changes in breathing pattern or color turning blue or pale
- Shaking that lasts longer than 10-20 seconds
If the movement stops when you touch the limb, it is almost always a benign tremor. If it continues despite your touch or involves the eyes or breathing, seek medical care immediately.
Why Is My Newborns Leg Shaking Causes When To Worry?
You should worry when the shaking is accompanied by specific warning signs. The isolated shake that stops is not an emergency. The following situations require immediate medical evaluation:
- Shaking that continues when you hold the leg still
- Shaking lasting more than 30 seconds
- Shaking accompanied by eye deviation, staring, or blinking
- Skin color changes, especially turning blue or very pale
- Shaking that happens when the baby is calm and content
- Lethargy or difficulty waking the baby after the episode
- Feeding difficulties, vomiting, or poor weight gain
- A fever (rectal temperature of 100.4°F or higher)
These signs can indicate an underlying condition such as neonatal seizures, metabolic imbalances, or an infection. Do not wait to see if it happens again. Call your pediatrician or go to the emergency room.
If the shaking is brief, stops with touch, and happens only during crying or startle, it is likely normal. You should still mention it at your next well-baby visit. Your doctor will want to hear a description of the movement.
Medical Causes of Leg Shaking in Newborns
When leg shaking is not normal jitteriness, several medical conditions may be responsible. These are less common but require prompt treatment.
Hypoglycemia (low blood sugar) is a frequent cause of tremors in the first days of life. Newborns have high energy needs. If feeding is delayed or insufficient, blood sugar can dip. This is easily treated with feeding or intravenous glucose in the hospital.
Hypocalcemia (low calcium) or low magnesium can also cause neuromuscular irritability. This leads to twitching and shaking. Blood tests can identify these imbalances quickly.
Neonatal abstinence syndrome (NAS) occurs when a baby was exposed to opioids or other substances during pregnancy. Withdrawal causes tremors, irritability, poor feeding, and high-pitched crying. This condition requires specialized medical management.
Neurological conditions such as hypoxic-ischemic encephalopathy (HIE), which results from reduced oxygen at birth, can cause seizures. Metabolic disorders and brain malformations are rarer causes. These are diagnosed with imaging and neurological exams.
Infections like meningitis or sepsis can also cause seizures in newborns. A fever is a red flag. Any newborn with a fever and shaking needs urgent medical care.
When the Shaking Is Normal: Benign Neonatal Sleep Myoclonus
There is a specific condition called benign neonatal sleep myoclonus. It looks like shaking or jerking, but it only happens during sleep. The movements stop immediately when the baby wakes up.
This condition is harmless. It does not affect development and requires no treatment. The key diagnostic feature is that the jerking ceases the moment the baby is aroused. Parents often mistake this for seizures, but it is a distinct and normal phenomenon.
If the jerking only happens in sleep and stops on waking, it is likely this benign condition. Still, a pediatrician should confirm the diagnosis to rule out other causes. Many parents find that recording a video of the episode helps the doctor make an accurate assessment.
What Should Parents Do During an Episode?
Staying calm is the first step. Your response matters for your ability to observe and report accurately.
If you notice your newborn’s leg shaking, do the following:
- Gently place your hand on the shaking leg to see if it stops
- Note the time the shaking starts and stops
- Observe the baby’s face, eyes, and breathing
- Take a video if you can — this is the most useful tool for your pediatrician
- Do not try to hold the limb still forcefully
- Do not shake the baby to stop the movement
After the episode, check the baby’s color and responsiveness. If the baby is alert and feeding normally afterward, the risk of a serious problem is lower. If the baby is difficult to wake or looks unwell, seek medical care.
Video recording is invaluable. Doctors cannot observe the movement after the fact. A clear video showing the pattern of movement, the duration, and whether it stops with touch helps the doctor distinguish a benign tremor from a seizure.
How Doctors Evaluate Newborn Leg Shaking
When you bring your baby in for evaluation, the doctor will take a detailed history. They will ask about the frequency, duration, and triggers of the shaking. They will also ask about feeding, birth history, and any family history of seizures.
The physical exam focuses on the nervous system. The doctor will check reflexes, muscle tone, and the baby’s level of alertness. Blood tests may be ordered to check glucose, calcium, magnesium, and electrolytes.
If seizures are suspected, the doctor may order an electroencephalogram (EEG). This test records brain activity and can detect abnormal electrical patterns. Imaging such as an ultrasound or MRI of the brain may be used if a structural problem is suspected.
Most newborns with normal jitteriness will have a normal exam and no further testing. The diagnosis of benign tremors is made based on the clinical picture. The absence of red flags and the cessation of movement with touch are usually sufficient to reassure parents.
Frequently Asked Questions
Why does my newborn’s leg shake while sleeping?
This is often benign neonatal sleep myoclonus, a harmless condition where jerking occurs only during sleep and stops immediately when the baby wakes. The newborn’s immature nervous system also causes normal twitching during light sleep.
When should I take my baby to the ER for leg shaking?
Go to the emergency room if the shaking continues when you hold the leg, lasts longer than 30 seconds, or is accompanied by eye rolling, staring, blue skin, or difficulty waking. A fever with shaking also requires immediate medical attention.
Can low blood sugar cause leg shaking in newborns?
Yes, low blood sugar is a common cause of tremors in newborns. It often resolves with feeding, but persistent shaking should be evaluated by a doctor to confirm the cause.
Is it normal for a newborn’s legs to shake when crying?
Yes, this is a normal response to the stress of crying in many newborns. The shaking should stop when you hold the leg or soothe the baby.
