'Startle' or Moro reflex.
The 'Moro reflex' (also known as the startle reflex) occurs in response to any sudden movement or loud noise. Your baby will fling their arms out, fan their fingers, extend their legs and then quickly pull their arms back in towards their body in an 'embrace' position. The reflex can sometimes cause them to tremor and cry and at times become quite upset.
This reflex can contribute to suddenly waking a sleeping baby, making it difficult to resettle them back to sleep. This is why some formal settling techniques believe in firm wrapping of the baby to help minimise this response, preventing the jerky movement from waking the baby unnecessarily.
The Moro reflex may be stimulated by your caregiver to test your baby's central nervous system development and muscle tone. This is done by your caregiver (or paediatrician) lifting the baby's shoulders up from the bed at a 45o angle, then allowing the baby's head to gently drop back into the caregiver's other hand. You may wish to think twice about testing for this reflex yourself, as it usually makes the baby cry, then the parents cry too!
The Moro reflex usually disappears by the time the baby is 8 to 10 weeks old.
When you place your newborn on his or her stomach, they will usually draw their legs up under their belly (as they were in the womb). They can then kick their legs out and often be able to shuffle and move in a crawling motion. (This is why you should never leave your baby unattended on something high like a bed or change table). If you apply firm pressure to the soles of their feet it will trigger a response to push forward. (This does not mean that your baby will be an early crawler!) The 'crawling reflex' is only present for the first 4 weeks and therefore lost before the baby is on the move and formally crawling