A: Newborns have more synapses, or connections, in their nervous system than adults do, which makes them more sensitive to their environment, says Romi Webster, a pediatrician at Children's Hospital Boston. This is the main reason why your newborn startles and twitches so easily at a sudden movement or loud sound. Young babies also have increased tone in their flexor muscles – if you extend your baby's leg, for example, it will likely jerk back into a bent position. This heightened muscle tone decreases over the first nine months of life, at the same time that motor coordination improves, allowing your baby smoother movements as he grows. Keep an eye out for startling that continues much beyond 4 to 6 weeks, says Webster, or excessive twitching that can't be stopped by putting your hand on the shaking limb. In those cases, it's advisable to take your baby to a doctor to make sure there's not an issue needing medical attention.
Does your baby ever jerk and twitch?