If your baby gets a sense of falling or hears a loud noise like a dog barking or door shutting, he will extend his arms and legs, open his fingers and arch his back. Then he will clench his fists and pull his arms to his chest. Your baby may also cry. There may also be effects you can’t see, like increased heartbeat and breathing. Some babies are more sensitive than others, too, so even a light touch could bring on the startle reflex at times.
You will probably test this reflex many times accidentally as loud noises are sometimes unavoidable, especially if you have pets and other children at home. Don’t be concerned if your baby doesn’t respond this way to every loud noise, though. And be aware that the reflex should disappear at around 2 to 4 months of age. If your baby doesn’t startle at all, you should contact your health care provider. This could be a sign that something is wrong with your child’s neurological system.
Also Known As: Startle Reaction or Moro Reflex (after German Pediatrician Ernst Moro)