What Is the Moro Reflex?

Medically Reviewed by Zilpah Sheikh, MD on December 06, 2023
7 min read

You may have noticed your baby being startled or reacting suddenly when you're trying to put them down to sleep. This is the Moro reflex, one of several normal reflexes that healthy babies are born with. This "startle reflex" is also one of the things your baby’s doctor checks for right after birth and during child health visits.

Reflexes are involuntary actions that your body does without you needing to think about it. There are many types of reflexes, and we are born with most of them. Newborn babies are born with several important reflexes, called primitive reflexes. These are essential for their development. Some are responses to actions while others are spontaneous movements.

When your baby’s head position suddenly shifts or if their head falls backward, they will throw out their arms away from their body and extend their neck. They also open their fingers. They will then quickly bring their arms back together, elbows bent, then relax their arms. Their fingers may also curl. Your baby may have a startled look on their face and may also cry. This reaction also happens when your baby is startled by a sudden movement, bright light, or loud sound. 

This is the Moro reflex. It was first described by Ernst Moro in 1918. It can be seen as early as 25 weeks after conception and is present by 30 weeks after conception.

The Moro reflex in babies disappears around 2 to 6 months of age when they're able to support their heads. As your baby’s brain matures and they gain better control over their movements, these reflexes are no longer needed.

Preterm babies typically have a weaker Moro reflex, and the reflex usually takes longer to go away than in babies born at full term. This is because premature babies may have poorer muscle tone and slower arm movements than a full-term infant. Your preterm baby's milestones will mirror what would have happened if they remained in the womb to reach full term (gestational age). Because of this, your baby may have the Moro reflex for longer than 6 months.

Other reflexes in newborns include:

The rooting reflex. When you touch or stroke your newborn’s cheek or a corner of their lip, they automatically turn their head toward that side and open their mouth. This reflex of following in the direction helps them to find the nipple for breastfeeding.

The sucking reflex. When something is placed in your baby’s mouth and it touches the roof of their mouth, they will start sucking. This reflex isn’t fully developed until about 36 weeks.

The grasping reflex. Stroking the palm of your baby's hands will cause them to close their fingers around yours. Similarly, they will curl their toes when you touch the bottom of their feet. The grasping reflex lasts until your baby is 5 or 6 months old.

The stepping reflex. When you hold your baby upright above a table or other firm surface, they might move their feet as if trying to walk or dance. This reflex goes away after about 2 months.

The tonic neck reflex. Also called the fencing position, this is when your baby turns their head and stretches the same side arm out long while bending the other arm at the elbow. This reflex lasts 5 to 7 months.

Your health care professional will do several tests to check on your baby’s development as part of their regular checkups. Reflexes are checked to ensure that the nervous system and the brain are developing well.

One of these tests is a Moro reflex test. Your baby will be placed lying face-up on a soft, padded surface or held in the doctor’s arms. The doctor will lift your baby’s head slightly above their body and let it gently fall into the doctor’s hand. This will make your baby feel like they're falling and their arms will extend and then draw back in rapidly as part of the Moro reflex. 

Some doctors may pull up gently on your baby’s arms and let them go. This also creates the feeling of falling and triggers the Moro reflex.

How to test the Moro reflex in an older child

An older child with a retained Moro reflex will have the same exaggerated startle reflex as a newborn. But in an older child, this oversized reaction will cause a surge of stress hormones that may cause:

  • Not being able to retain information or learn well
  • High levels of anxiety
  • A compromised immune system that can trigger allergies
  • Extreme sensitivity to light, noise, touch, movement, or hot and cold

 

Parents may be concerned when they see the Moro reflex happen for the first time. This is a normal reflex in babies. Nothing needs to be done when your baby startles. Some babies may even stop crying on their own. Other babies may need to be soothed and comforted, such as by holding them or talking softly to them.

The moro reflex can be triggered when you’re trying to put your baby to sleep. For example, when you lean over to lay your soundly sleeping baby down in their crib, they startle awake because of the sensation of falling. At other times, they may be sleeping soundly and startle awake, sometimes even by their own movements.

Try these tips if your baby's reflexes are stopping them from sleeping soundly:

Lower horizontally. Try lowering your baby into their crib horizontally, so that you don’t tilt their head backward.

‌Hold your baby close. Keep your baby as close as possible to your body as you lower them. Release them only when their body is touching their mattress. 

‌Swaddling. To help your baby sleep better, you can try swaddling. Wrapping your baby in a swaddling cloth secures their arms so that they won’t startle and fling their arms away from their body. This can calm your baby and help them to sleep better. Make sure your baby is placed on their back to reduce the risk of sudden infant death syndrome, or SIDS.

You might be able to stop the Moro reflex without swaddling by giving your baby a pacifier at naptime or bedtime.

Don’t worry if your baby doesn’t startle every time there’s a loud noise or bright light. But if a baby doesn’t have any Moro reflex at all, it could be because of a medical problem. These include a birth injury, problems with the brain, or general muscular weakness. 

Abnormal Moro reflex. A Moro reflex that happens only on one side of the body (asymmetrical) may be because of an injury, such as damage to a nerve or the spinal cord, or a fracture to the collarbone. If your baby’s Moro reflex doesn’t go away after 6 months, this could be a sign of other problems such as a delay in the development of their motor skills or cerebral palsy

Exaggerated Moro reflex. Babies whose startle reflex triggers an extreme response to sudden movement, noise, or touch may have a rare inherited disorder called hyperekplexia. A Moro reflex that comes with spasms, stiffness, or rapid blinking is a sign of this neurological disorder. 

Moro reflex beyond 6 months. Visit your pediatrician if your baby retains the Moro reflex longer than 6 months. It may be a developmental delay or a symptom of a nervous system issue. Autism, attention deficit hyperactivity disorder, and learning and developmental disorders have been linked to an ongoing Moro reflex. 

Startle reflex vs. infantile spasms 

Infantile spasms – a rare form of epilepsy – are a series of small seizures that can affect a baby's development. They look very much like the Moro reflex and are easy to miss. Here's how to tell the difference:

  • The Moro reflex is seen in newborn babies, while infantile spasms usually start to appear between the ages of 3 months and a year.
  • The startle reflex is triggered by sudden noise and movement or bright light and is a single event. Infantile spasms only last a couple of seconds but happen one after another.
  • Babies usually have infantile spasms around sleep times, usually when waking, and will cry or be cranky after.
  • Your baby may no longer show signs of previous milestones.
  • The startle reflex reappears in your baby after being absent for weeks or months. Take your baby to their pediatrician right away.

 

The Moro reflex, or startle reflex, is a normal way newborn babies react to stimulation. It starts when your baby is still in the womb and goes away as your baby's nervous system matures, usually around 2 to 6 months. Your baby's pediatrician will test for the Moro reflex at their first and later visits. If your baby doesn't have a Moro reflex, or has one on only side, it means something is not right. If your baby has an abnormal startle reflex, your pediatrician will probably ask about your labor and delivery, your family's history, and any unusual symptoms you've noticed in your baby.