Newborn babies don't shiver because they're cold. They shiver for another reason entirely.

If you’ve seen your newborn shiver this winter, your first instinct was likely to hold them close to your body or to wrap them in a warm, toasty blanket.

That seems only natural, right?

Except newborns don’t actually shudder due to the cold.

It’s unclear at precisely which age we develop the ability to shiver, though most of us seem to by the time we’re toddlers as a way of keeping warm (shivering causes rapid contraction and expansion of the muscles which in turn generates heat).

As paediatrician Dr Daniel Golshevsky explained to Mamamia, newborns instead rely on a layer of what’s called ‘brown fat’, or adipose, which burns off and in the process – yep – generates heat.

“The lack of the ability to shiver is one of the reasons we must be very careful to monitor and control a baby’s temperature with clothing, wraps, etc,” he said.

“Babies lose heat faster than older children and adults, plus they can’t exactly move to a warmer place or throw on a jumper.”

How to get your baby to sleep. (Post continues below.)

This is not to say that newborns don’t make shuddering movements, just that there are other reasons that they occur.

“Due to slowly developing muscle control, babies will often shudder their limbs when they get excited, want something or move in any way. Their movements are also very jolty and not smooth, which can sometimes be misinterpreted as a seizure,” Dr Golshevsky explained.

“Another very common time to observe unusual, jerky movements is as a baby falls asleep and as they begin to wake. These movements are called myoclonus, which comes from the latin myo, which means muscle, and clonus, meaning rapid on/off succession. Myoclonic jerks can be very frightening to observe for some parents.”

Image: Getty.

The key, Dr Golshevsky said, is get to know your baby's movements - especially the timing of them and your little one's general behaviour when they occur.

"In a child with normal development and perfect health, you should only be concerned by a sudden change in movement pattern or behaviour," he said. "But also by shakes that last longer than 20 seconds or those that are associated with injury, illness, fever, loss of consciousness, unusual eye movements or if the baby's breathing has stopped.

These are suggestive of a seizure, especially if the baby is inconsolable, vomits or sleeps for unusually lengthy periods afterwards.

"In any of these settings - or for any concerns - have the baby seen by your doctor," he said.

Dr Golshevsky's tip: If you are concerned about your baby's shuddering movements record a video on your phone to show to your doctor. "It's always helpful."