Dr. Sarah Mitchell
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The Startle Reflex in Babies: Everything You Need to Know

What is the startle reflex in babies?

The infant startle reflex goes by many names.  Also known as the newborn startle reflex and  the Moro reflex.

This is a primitive reflex that is present at birth. This reflex is referred to as the Moro reflex, or startle reflex.  It is elicited by pulling up on the infant’s arms while on their back and letting go of the arms causing the sensation of falling (Zafeiriou et al 2004)  

The reflex is elicited by a sudden stimuli such as noise or a movement.  The normal Moro reflex starts with the abduction of the upper extremities and extension of the arms.  Meaning your baby’s arms move away from the body and the arms get straight.  Then the fingers extend, and there is a slight extension of the neck and spine. After this initial phase, the arms adduct and the hands come to the front of the body before returning to the infant's side.

The key with the reflex is that the arms pull back to the body.  This is not to be confused with babies putting their arms over head and flailing.  That is very common and is due to lack of arm control and coordination which improves with age. 

When do babies lose the startle reflex? 

The reflex is present in full-term infants and begins to disappear by 12 weeks with complete disappearance by six months. (Futagi et al, 2012)

There can be a significant reduction in the reflex around 4 months.  Lack of startle reflex at birth is a serious concern and can signify a variety of compromising conditions. 

Why do babies have the startle reflex? 

The Moro reflex is an involuntary protective motor response against abrupt disruption of body balance or extremely sudden stimulation. (Futagi et al 2012)

Is the startle reflex bad for babies? 

It is a natural, primitive reflex designed to protect the baby.

3 Ways to Help Your Baby Avoid the Moro Reflex

  1. Swaddling!  One of the main purposes of swaddling is to help control the sudden response of the arms which can often wake a sleeping or dozy newborn baby.

  2. When placing your baby on the back, make sure you place her feet, then bottom and then head.  If you lead with the head, dropping it below the level of the body, this will elicit the startle reflex.

  3. Avoid sudden drops, loud noises or sudden movements which can elicit the response. This is when white noise can be helpful to block out sudden loud noises which can elicit the response.  

The startle reflex is one of the reasons babies can’t be independent sleepers until after 4 months of age.  Babies need their hands to be able to help them self-soothe and that motor control is disrupted by a strong moro reflex. 

Major reference used in this article:

Futagi Y, Toribe Y, Suzuki Y. The grasp reflex and moro reflex in infants: hierarchy of primitive reflex responses. Int J Pediatr. 2012;2012:191562.

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