Startle response

Alternative names
Moro reflex; Startle reflex; Embrace reflex

Definition
Moro reflex is a primitive reflex that is present at birth and typically disappears in the first few months of life. (See also infantile reflexes.)

Considerations

The Moro reflex may be demonstrated by placing the infant face up on a soft, padded surface. The head is gently lifted with enough traction to just begin to remove the body weight from the pad (Note: the infant’s body should not be lifted off the pad, only the weight removed).

The head is then released suddenly, allowed to fall backward momentarily, but quickly supported again (not allowed to bang on the padding). The infant may have a “startled” look, and the arms fling out sideways with the palms up and the thumbs flexed. As the reflex ends the infant draws the arms back to the body, elbows flexed, and then relaxes.

Common Causes

This is a normal reflex present in newborn infants. Absence of the Moro reflex in an infant is abnormal. Presence of a Moro reflex in an older infant, child, or adult is also abnormal.

Two-sided absence of the Moro reflex suggests damage to the central nervous system (brain or spinal cord).

One-sided absence of the Moro reflex suggests the possibility of a fractured clavicle or injury to the brachial plexus, which can occur because of birth trauma. Conditions associated with brachial plexus injury include Erb’s palsy and Erb-Duchenne paralysis. Paralysis on one side of the body may also produce an asymmetrical Moro reflex.

Home Care

It is NOT necessary to ehck for a Moro reflex at home. Your doctor will check at the baby’s visit.

Call your health care provider if

     
  • you suspect your infant may have a fractured clavicle or a brachial plexus injury (causing loss of the Moro reflex on one side). What to expect at your health care provider’s office The medical history will be obtained and a physical examination performed. Medical history questions may include:
       
    • history of the labor and birth  
    • detailed family history  
    • other symptoms

    Note: An abnormal Moro reflex is usually discovered by the health care provider.

    PHYSICAL EXAMINATION
    The Moro reflex will be evaluated. The muscular system and nervous system may need to have detailed examination, if the reflex is absent or abnormal.

    Diagnostic tests, in cases of decreased or absent reflex, may include:

       
    • clavicle or shoulder joint X-ray  
    • tests for disorders associated with brachial plexus injury

    AFTER SEEING YOUR HEALTH CARE PROVIDER
    You may want to add a diagnosis related to an abnormal Moro reflex to your child’s personal medical record.

    Johns Hopkins patient information

    Last revised: December 2, 2012
    by Arthur A. Poghosian, M.D.

    Medical Encyclopedia

      A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0-9

    All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.