The first few weeks of newborn life are often a startling experience for the parent — those sudden full-body jerks, the chin-quivering after a cry, the little tremor in the hand that won't quite settle. Most of it is built-in newborn neurology. A small subset of patterns is worth telling your midwife or GP about. For a wider view, see our complete guide to child health.
The Moro Reflex
The Moro is one of the primitive reflexes present from birth — hard-wired motor patterns that disappear as voluntary control develops. It's triggered by:
- A sudden loud noise
- A change in head position (most commonly when you lower the baby onto a surface and momentarily let go of the head)
- A bright light or sudden loss of support
The response is distinctive and symmetrical: both arms fling outward with fingers splayed, then sweep back inward toward the chest in a brief embracing motion. It's often accompanied by a brief cry. The whole sequence takes a second or two.
The Moro is present from birth and typically fades between three and four months as the cortex starts taking over from the brainstem reflex circuitry. A few clinical points worth knowing:
- An asymmetric Moro — one arm moving and the other not, or one arm moving less — can indicate a brachial plexus injury (Erb's palsy from a difficult delivery) or a fractured clavicle. Worth flagging at the NIPE check or to the midwife.
- An absent Moro in a newborn is unusual and prompts a neurological review.
- A persistent Moro past six months can be a soft sign of underlying neurological issues, though some otherwise typical babies retain it slightly longer.
Normal Newborn Trembling
Many newborns show fine trembling — particularly of the chin, lower lip, and hands — when they cry, after feeds, or when they're cold or being undressed. The mechanism is straightforward: the central nervous system is still myelinating, and motor regulation hasn't fully calibrated. The tremor is the absence of fine inhibitory control, not a sign anything has gone wrong.
Features that confirm it's the normal kind:
- It happens with or just after a clear trigger — crying, a feed, a temperature drop, a startle
- It stops when you gently hold the trembling limb (or when the trigger ends)
- The baby is otherwise alert, feeding well, and looking at you between episodes
- It eases off across the first few weeks and is usually gone by two to three months
Jitteriness vs Seizure
This is the question that brings parents to the front desk of the maternity unit at 2 a.m. The clinical distinction is reasonably reliable:
Jitteriness:- Stops when you gently hold the limb
- Triggered by something (sound, touch, being uncovered)
- No abnormal eye movements
- Baby is responsive during the episode
- Continues even when you hold the limb
- Often happens at rest, without a trigger
- May involve eye deviation (eyes drifting to one side or fluttering), repetitive blinking, or staring
- Baby may look "absent" or unresponsive during the episode
- May include unusual repetitive movements: lip-smacking, sucking when not being fed, bicycling movements of the legs, brief breathing pauses (apnoea)
Neonatal seizures are uncommon but matter — they can be subtle. The textbook tonic-clonic shaking is rare in newborns; the more usual presentations are subtle ones (the bicycling, the lip-smacking, the staring spells). When in doubt, get the baby seen, and if you can capture a phone video of an episode, do — clinicians find them genuinely useful.
When Jitteriness Has a Cause
If trembling is frequent, severe, or paired with other symptoms, the differential includes:
- Hypoglycaemia (low blood glucose). Particularly relevant in babies who are small for gestational age, premature, born to diabetic mothers, or feeding poorly. Usually identified in the first day or two on the postnatal ward.
- Hypocalcaemia (low calcium). Causes neuromuscular irritability and is more common in preterm or unwell babies.
- Drug withdrawal — Neonatal Abstinence Syndrome. In babies whose mothers used opioids, methadone, benzodiazepines, or some antidepressants in pregnancy. Tremor is one of several signs (poor feeding, irritability, sneezing, loose stools).
- Infection. Sepsis can present with non-specific neurological signs in a newborn.
- Hyperthyroidism in babies of mothers with Graves' disease.
Most of these are caught in the maternity unit because the baby is already being monitored for risk factors. A baby discharged home and developing new persistent jitteriness is the scenario that needs a fresh look.
When to Seek Help
Contact your midwife or GP — or NHS 111 / 999 if it feels acute — if:
- The trembling is frequent or prolonged and doesn't fit the "with crying / feeding / cold" pattern
- Movements don't stop when you gently hold the limb
- There are eye deviations, prolonged staring, or repetitive blinking
- Skin colour changes during episodes (going dusky or pale)
- There are pauses in breathing during the episodes (apnoea)
- The baby seems less responsive during or after episodes
- One side moves and the other doesn't
The default benign newborn jerkiness — the chin-quiver after a feed, the symmetrical fling at a slammed door — is harmless, self-limiting, and a sign that the nervous system is maturing roughly on schedule. The pattern that needs attention is the one that ignores the rules above.
Key Takeaways
The Moro (startle) reflex — arms flung outward then drawn back as if for an embrace — is normal, present from birth, and fades by three to four months. Fine trembling of the chin, lips, or hands when crying, feeding, or cold is also normal and fades over the first weeks. The clearest test for distinguishing benign jitteriness from a seizure: gently hold the trembling limb. Jitteriness stops; seizure activity does not. Persistent jitteriness, asymmetric movements, eye deviation, or breathing pauses during the episodes need urgent assessment.
