New parents often observe movements in their newborn that cause alarm — the dramatic startle reflex, the trembling chin after a cry, the brief rhythmic trembling of a limb. Most of these movements are entirely normal features of the immature neonatal nervous system, but understanding which movements are reassuring and which warrant medical attention requires some specific knowledge that is not always provided during early discharge from hospital.
Healthbooq supports parents through the sometimes bewildering observations of the newborn period with evidence-based guidance on which findings are normal and which warrant discussion with a health visitor or GP.
The Moro (Startle) Reflex
The Moro reflex is one of the most dramatic and startling of the newborn reflexes. It is elicited by a sudden change in position or a loud noise and consists of a rapid bilateral arm extension (arms flying out to the sides), followed by a brief embrace-like return of the arms to the midline, often accompanied by a brief cry. It is an involuntary, normal reflex mediated by brainstem circuits, reflecting the immaturity of the cortical motor system that will eventually suppress it.
The Moro reflex is present from birth and typically disappears between three and six months, as the developing cortex increasingly inhibits primitive reflexes. Its asymmetry — one side responding less than the other — can indicate a neurological or orthopaedic abnormality (such as an Erb's palsy from a difficult birth) and warrants assessment.
Jitteriness in Newborns
Neonatal jitteriness — rapid, rhythmic trembling affecting the chin, jaw, limbs, or tongue — is seen in up to forty per cent of normal newborns and is the most common movement disorder in the newborn period. It is most prominent in the first few days of life and reduces in frequency and intensity over the first weeks as the nervous system matures.
The key distinguishing feature of benign jitteriness from seizure activity is that jitteriness is stimulus-sensitive (it is triggered by handling, noise, or cold) and is suppressed by gentle restraint — holding the limb still stops the movement. Seizures, by contrast, are not triggered by stimulation, are not suppressed by restraint, and are often associated with other features such as eye deviation (the eyes moving to one side), rhythmic eye blinking, colour changes (pallor or cyanosis), or altered responsiveness.
Jitteriness that is very pronounced, very persistent beyond the first two to three weeks, or associated with any of the features suggesting seizure rather than jitteriness warrants prompt medical assessment.
When Jitteriness May Indicate an Underlying Problem
While most neonatal jitteriness is benign, in some cases it reflects an underlying metabolic or neurological cause. Low blood sugar (hypoglycaemia) is one of the most common metabolic causes and is more likely in babies of diabetic mothers, large-for-gestational-age or small-for-gestational-age babies, premature babies, and babies who are cold, not feeding well, or persistently jittery. Hypoglycaemia in newborns can cause neurological injury and requires prompt assessment; if there is any concern about the baby's feeding, colour, or energy alongside jitteriness, a GP or midwife should be contacted.
Low calcium (hypocalcaemia) can also cause neonatal jitteriness and is more common in babies born to vitamin D-deficient mothers.
Recognising a Newborn Seizure
Newborn seizures are subtle and do not typically resemble the convulsions seen in older children. Features that may indicate neonatal seizure include: repetitive, stereotyped movements that the baby does not seem aware of (cycling movements of the legs, sucking or chewing movements, rhythmic blinking); eye deviation; colour change (pallor, cyanosis, or redness); breath-holding; and abnormal changes in muscle tone. These features require emergency medical assessment.
Any newborn who appears acutely unwell — abnormally floppy, unusually pale, not responding normally, or having abnormal repetitive movements — should be assessed urgently, with 999 called if the baby is very unwell.
Key Takeaways
Trembling, jitteriness, and the Moro (startle) reflex are common normal findings in newborns that frequently cause parental anxiety. Jitteriness in newborns — rhythmic, rapid trembling of the chin, limbs, or jaw — is seen in up to forty per cent of normal newborns and reflects the immaturity of the neonatal nervous system. It is almost always benign and self-limiting. However, abnormal movements in newborns — particularly those that are not stopped by gentle restraint, are associated with eye deviation or changes in colour, or persist beyond the early weeks — can indicate seizure activity and warrant prompt medical assessment.
