The Moro Reflex in Newborn Babies

The startle or Moro reflex, which is named after German pediatrician Ernst Moro, is just one of several involuntary movements in newborns. Newborns may seem to come into the world as defenseless creatures, but they're actually equipped with a variety of innate reflexes that help ensure their safety—primarily by alerting their parents for help when needed.

The startle reflex is the baby's response to the sensation of falling and/or stimuli in their environment, such as loud, potentially threatening sounds and bright lights. When exhibiting the Moro response they will flex and thrust out their arms, hands, and legs, show a startled expression, and possibly cry. The reflex protects the baby by getting the attention of caregivers and may help to lessen the impact of a fall.

What the Moro Reflex Looks Like

From birth, when newborns are exposed to startling environmental stimuli, they will instinctively extend their arms and legs, open their fingers and arch their backs. Then, newborns will clench their fists and pull their arms to their chests. As noted above, they also display a tell-tale startled expression. Babies exposed to loud noises or other stimuli may also cry.

If you want to see the startle reflex in action simply observe newborns when they feel as if they might fall down, such as when being put in a car seat or crib, or when they hear an unsettling or loud noise, such as a dog barking or a door shutting. This involuntary reflex will usually happen right away in response to stimuli.

The startle reflex doesn't end with this reaction, however. Babies who hear loud sounds may also experience effects their parents can’t see, such as an increased heartbeat or heavy breathing. Some babies are more sensitive than others and will react with more intensity and more often.

For sensitive babies, even a light touch may bring on the startle reflex. This isn't necessarily a bad thing, but it does alert parents to the fact that their little one may be particularly sensitive to sensory input.

What to Do When a Baby Startles

Even though it may look upsetting for your baby, remember that it is normal for a baby to startle when they hear a loud noise or when you are placing them down on their backs to sleep. Sometimes, they may even provoke the response in themselves due to their own abrupt movements.

Nothing needs to be done when a baby startles. However, they will likely respond well to calming measures, like touching, holding, or singing to them. Note that some babies may stop crying on their own after they are startled. Others may need more intervention, such as being picked up, in order to stop crying and/or be comforted. If the startle reflex is interfering with your baby's sleep, parents can try swaddling, which may render the reflex less jarring.

Problems With the Moro Reflex

Most parents will observe the Moro reflex accidentally while caring for their baby, as bright lighting and loud noises are sometimes unavoidable, especially if you have pets and other children in the home or live on a busy street. However, parents shouldn't intentionally startle their child to see if the newborn has the reflex. There is no need as doctors will check babies for this reflex as a part of their baby’s regular check-ups.

Also, parents should not be concerned if babies don’t perform the startle reflex in response to every loud noise—but they should do it sometimes. As long as they sometimes display the response, not doing it every time doesn't indicate there's a problem with the baby. The child simply may not startle easily or may do so in a subtle manner that a parent might miss.

Keep in mind that if your baby is a preemie, the timing of their startle reflex may be different than is typical for full-term infants. The reflex's onset may be delayed and the reflex may stick around longer than normal due to the gap between your baby's birthday and their developmental age.

However, if you notice that your baby does not seem to show this reflex at all, or if the motion is only on one side of the body, parents should alert their doctor. While very rare, absence or one-sidedness of the reflex could indicate a problem, such as a birth injury, spastic cerebral palsy, a problem with the neurological system, infection, or localized injury (often the cause of asymmetrical reflex). Again, it's very unusual for the reflex to be truly absent or one-sided.

When It Disappears

Typically, this reflex begins to disappear around two months of age but often remains until three or four months. If it lasts beyond six months, let your pediatrician know as they will want to confirm that nothing else is wrong. Additionally, parents should contact their doctor if anything else about their child's reflexes concerns them.

A Word From Verywell

The startle reflex is one of many involuntary movements babies have upon entering the world. Be assured that the Moro reflex is normal, developmentally appropriate, and healthy—and does not hurt your baby. In fact, these instinctive movements may help babies bond to family members and get the love and care they need.