The startle reflex, also known as the Moro reflex, typically stops or disappears between 3 to 6 months of age in infants. This reflex is a primitive reflex present from birth and is an early indication that the baby's nervous system is developing properly. It usually peaks within the first month and begins to fade around 2 to 4 months, disappearing completely by about 6 months. After this time, the reflex is integrated into more mature postural reflexes that control balance, coordination, and sensory-motor development. If the startle reflex persists beyond 6 months, it may indicate developmental concerns and should be discussed with a pediatrician. The reflex involves the baby suddenly extending arms and legs and then drawing them back in response to a sudden noise or movement, typically lasting only a few seconds.