The Moro reflex — also called the startle reflex — causes a newborn to suddenly fling their arms out, spread their fingers, then bring the arms back in as if grabbing something. It is one of the most striking of all newborn reflexes.
What the Moro Reflex Is
The Moro reflex is triggered by a sudden movement, sound, or change in head position. The baby's arms fly outward with hands open, then draw back toward the body. The legs may extend, then flex. The baby may cry briefly. The whole sequence lasts 1–2 seconds.
Why Babies Have It
The Moro reflex is a primitive survival reflex. In primate infants, it evolved as a way to grab onto the mother if they felt they were falling. The sudden feeling of falling triggers the reach-out response. In human newborns, it serves as an indicator of neurological health — a weak or absent Moro reflex may indicate a brainstem or motor problem.
Common Triggers
- Being placed down suddenly (feeling of falling)
- Sudden loud sound
- Sudden bright light
- Head falling backward unexpectedly
- Transition between sleep cycles (partial arousal)
Why It Wakes Babies from Sleep
The Moro reflex can be triggered at the transition between sleep cycles when the baby experiences a momentary feeling of falling as their muscle tone changes. This is one of the main reasons newborns wake after 45 minutes — the reflex startles them awake just as they are cycling into lighter sleep.
How Swaddling Helps
Swaddling works because it contains the arms against the body, preventing the full Moro response. When the arms cannot fly out, the reflex cannot complete its arc — the baby is less likely to startle themselves awake. Use a snug but hip-healthy swaddle that allows the legs to flex and spread.
| Swaddle Method | Notes |
|---|---|
| Traditional swaddle blanket | Arms in or arms out — keep hips loose |
| Velcro swaddle wrap | Quick and consistent — popular in Singapore |
| Arms-up swaddle | Allows hand-to-mouth soothing |
| Transition swaddle | One arm out for babies starting to roll |
When the Moro Reflex Disappears
The Moro reflex typically fades between 3 and 6 months as the nervous system matures and cortical inhibition develops. If it persists beyond 6 months, this may indicate a neurodevelopmental concern worth discussing with your doctor.
Safety note
Stop swaddling as soon as your baby shows any sign of rolling — typically around 3–4 months. A swaddled baby who rolls cannot reposition themselves and may suffocate.