Moro reflex

Alternative names:

startle response; startle reflex; embrace reflex

Definition:

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 arms are 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 arms are then released suddenly. 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.

The Moro reflex may be abnormally present in Tay-Sachs disease.

Note: There may be other causes of an abnormal Moro reflex. This list is not all inclusive, and the causes are not presented in order of likelihood. The causes of this symptom can include unlikely diseases and medications. Furthermore, the causes may vary based on age and gender of the affected person, as well as on the specific characteristics of the symptom such as quality, time course, aggravating factors, relieving factors, and associated complaints. Use the Symptom Analysis option to explore the possible explanations for an abnormal Moro reflex, occurring alone or in combination with other problems.

Update Date: 02/09/00
Updated by: J. Gordon Lambert, MD, Associate Medical Director, Utah Health Informatics and adam.com editorial