You lay them down, gently, slowly, holding your breath the whole way - and just as their back touches the mattress, both arms fly out to the sides like they're bracing for a fall. Then the cry. Then you pick them back up, certain you've done something wrong.
You haven't. This is the Moro reflex, one of the most dramatic-looking - and most normal - things a newborn does.
What it actually is
The Moro reflex is an involuntary startle response present from birth, triggered by a sudden change in position, a loud noise, or the sensation of falling. The arms fling outward, the fingers spread, the back arches slightly, and then the arms draw back in toward the body - usually followed by crying, because it's a genuinely startling sensation for a baby with no context for what just happened.
It's one of several primitive reflexes doctors check for at birth precisely because its presence (and its disappearance on schedule) tells them something useful about neurological development.
Why babies have it at all
The leading theory is that it's an evolutionary holdover - a grasping reflex that would once have helped a falling infant cling to a caregiver. Whether or not that's the full explanation, it serves as a useful, measurable sign that the nervous system is wiring up as expected.
It's most active in the first couple of months and gradually fades as voluntary muscle control develops, usually disappearing somewhere between 3 and 6 months.
What sets it off
- Being laid down, even gently - the change in support is often enough
- A loud or sudden noise nearby
- A sudden bright light or shift in position
- Sometimes nothing you can identify at all - their own arm movement can startle them
How to make bedtime a little less dramatic
- Swaddling snugly (arms in) contains the startle and helps many babies settle faster
- Keep one hand on their chest for a beat after laying them down, rather than removing contact all at once
- Lower them slowly and land the bottom first, then the head, rather than a flat drop
- A supportive sleep environment with white noise can reduce how often the reflex fires from ambient sound
When to mention it to your MCH nurse
A strong, symmetrical Moro reflex in the early months is a good sign, not a concerning one. Worth flagging at a check-up if it seems absent altogether, noticeably one-sided, or hasn't faded by around 6 months - any of which your nurse can assess properly in context.
For now, the flailing arms and the offended little cry are just your baby's nervous system doing exactly what it's supposed to. Swaddle if it helps, and know that you didn't startle them - their own arms did.