Quick answer: The Moro reflex is an involuntary startle response where the baby’s arms fling outward then return inward when they sense sudden movement or loss of support. It’s present from birth, peaks in the newborn period, and typically fades by 3–6 months.
The mechanism
The Moro reflex is triggered by any sudden change in sensory input that the brainstem interprets as a threat — a sudden movement, a loud noise, a change in head position, or the sensation of falling. The response: both arms extend outward simultaneously (abduction) with hands open; then the arms return toward the centre (adduction) as if grasping. The primitive evolutionary function is thought to be grasping for the mother — an infant that fell would reach out for something to catch. The reflex is mediated by the brainstem and reticular activating system; cortical inhibition develops over the first months and progressively suppresses it.
The Moro reflex and newborn sleep
The Moro reflex is the primary reason newborns wake themselves during sleep. As the baby moves through the natural sleep cycle transition from deeper to lighter sleep (occurring approximately every 45–60 minutes), small body movements occur — these trigger the reflex, arms fling out, the baby startles awake and cries. This is exactly what swaddling prevents: containing the arms stops the Moro reflex from activating fully, allowing the baby to transition through the sleep cycle without fully waking. Swaddling’s effectiveness is directly tied to this mechanism — as the reflex fades at 3–4 months, the primary sleep rationale for swaddling diminishes.
Assessment and when it raises a concern
The Moro reflex is assessed at the NIPE newborn check by allowing the supported head to briefly fall back a few centimetres. A symmetric, brisk response is normal and expected. Asymmetric Moro (only one arm extends) can indicate a birth-related nerve injury (brachial plexus injury, Erb’s palsy) and warrants assessment. A Moro reflex absent in a term baby, or persistently present beyond 6 months, is worth discussing with a doctor or pediatrician. The gradual fading of the reflex is monitored at the 6–8 week check.
Accidentally triggering it
The Moro reflex is most commonly accidentally triggered during: putting the baby down when the head isn’t fully supported and the baby senses backward head movement; sudden loud sounds near the sleeping baby; changing the baby on an unstable surface; or lifting the baby without ensuring the head is supported from the start. Full head and neck support during all handling reduces accidental Moro triggering.
Frequently Asked Questions
My baby’s Moro reflex seems very strong — is that a concern?
No — a strong, symmetric Moro reflex in a newborn is normal. Intensity varies between babies. A very startly baby who wakes themselves frequently from sleep is at the stronger end of normal. Swaddling is particularly helpful for these babies.
Can Moro reflex be confused with a seizure?
Sometimes parents confuse them. Moro reflex: triggered by external stimulus; the baby wakes and cries; symmetric arm movement; resolves immediately. Neonatal seizures: typically not triggered by external stimuli; may involve rhythmic repetitive movement; may include eye deviation or changed breathing; the baby’s responsiveness during the episode is altered. If you’re concerned about any episode, describe it precisely to your doctor — they can distinguish clinically.
My 2-month-old still startles a lot — normal?
Yes — the Moro reflex is expected and fully normal at 2 months. It begins to diminish at around 3 months and fully resolves by 5–6 months.
Related Reading
- Swaddling a baby: step-by-step guide and when to stop
- 1 month old baby: milestones, sleep & feeding guide
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