A newborn’s leg or chin often trembles or shakes uncontrollably. This phenomenon, frequently called “jitteriness” or “tremor,” is a common observation in the first few weeks of life. While most of these movements are harmless reflections of a developing body, recognizing signs that might indicate a serious issue is important. This article distinguishes between expected, normal jitters and characteristics that require immediate medical attention.
The Normal Jitters: Benign Causes of Leg Tremors
Most leg tremors in newborns are physiological, resulting from the normal process of growth and development. The primary reason is the immaturity of the infant’s central nervous system (CNS). Nerve pathways between the brain and muscles are not fully myelinated—the process of coating nerve fibers with a fatty sheath for efficient signal transmission.
This lack of inhibitory control means a minor stimulus can cause an exaggerated, involuntary muscular response, such as a tremor or jerk. These movements are typically fine, quick, and small. They most often occur when the baby is upset, crying, or startled, and usually disappear within the first few weeks of life as the CNS matures.
Excitement and environmental factors can also trigger these benign movements. The Moro reflex, or startle reflex, is a natural response to a sudden loud noise or feeling of falling. This reflex involves the baby extending and then pulling their limbs back in, which may include a noticeable leg movement that looks like shaking. Additionally, being cold can cause a baby to shiver or display jitters as the body attempts to regulate temperature.
A temporary drop in blood sugar, known as transient hypoglycemia, can induce tremors, especially if a feeding has been delayed. Once the baby is fed, blood sugar levels stabilize, and the shaking quickly resolves. Benign neonatal sleep myoclonus is another common, non-harmful cause, characterized by brief, rhythmic jerks of the limbs that occur exclusively during sleep.
How to Distinguish Benign Shaking from Serious Concerns
Parents can use a simple test to distinguish common jitters from more concerning movements. The most telling characteristic of a benign tremor is that the movement can be stopped by gently holding the limb. If you gently restrain the baby’s leg, the jittering or shaking should cease immediately.
The context in which the movement occurs is also a helpful differentiator. Benign jitters are often provoked by external factors, such as a sudden noise, a change in position, or crying. If the movement starts only when the baby is stimulated or upset, it is more likely to be a normal jitter.
Normal jitters are brief, typically lasting only a few seconds, and do not involve a change in the baby’s state of consciousness. If the baby remains alert and responsive during the shaking, this suggests the movement is not a seizure. Movements that continue despite gentle restraint, or those that occur when the baby is calm and resting, warrant closer observation.
When Leg Shaking Signals a Medical Emergency
Certain characteristics of leg shaking are considered red flags and necessitate immediate medical consultation. A movement that is sustained, rhythmic, and continues even when the limb is held firmly is a significant warning sign, as this is the hallmark of a seizure. Infant seizures present as repetitive, clonic jerks that do not stop with touch.
The presence of other symptoms alongside the shaking indicates a medical emergency. These include changes in consciousness, such as difficulty waking up or appearing disoriented, or abnormal eye movements, like staring or tonic gaze deviation. A seizure may also be accompanied by a change in skin color, such as a bluish tint around the lips, or difficulty breathing.
Persistent, coarse tremors may be a symptom of underlying metabolic disorders, such as severe hypoglycemia, hypocalcemia (low calcium), or drug withdrawal syndrome. Immediate medical help is required if a baby exhibits tremors along with other signs of severe illness, such as a high or low temperature, lethargy, poor feeding, or a refusal to feed, especially if they are under eight weeks old. Parents should call emergency services if the baby has a fit for the first time or if the shaking is accompanied by an inability to wake the baby.