Health Encyclopedia

Moro reflex

Definition

Moro reflex is type of involuntary response that is present at birth. It normally disappears after 3 or 4 months.

Alternative Names

Startle response; Startle reflex; Embrace reflex

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 support 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 its 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 brain or spinal cord.

One-sided absence of the Moro reflex suggests the possibility of a broken shoulder bone or injury to the group of nerves that run from the lower neck and upper shoulder area. Conditions associated with such nerve injury include Erb's palsy and Erb-Duchenne paralysis. Loss of muscle function on one side of the body may also produce an asymmetrical Moro reflex.

Home Care

It is not necessary to check for a Moro reflex at home. Your doctor will check this reflex during an office visit.

Call your health care provider if

Call your health care provider if you think your baby may have a broken shoulder bone or injury to the nerves that run from the lower neck and upper shoulder area (brachial plexus injury), which can cause the loss of the Moro reflex on one side.

What to expect at your health care provider's office

An abnormal Moro reflex is usually discovered by the health care provider. The health care provider will perform a physical exam and ask questions about the child's medical history. Medical history questions may include:

History of the labor and birth
Detailed family history
Other symptoms

If the reflex is absent or abnormal, further tests may need to be done to examine the child's muscles and nerves. Diagnostic tests, in cases of decreased or absent reflex, may include:

Shoulder x-ray
Tests for disorders associated with brachial plexus injury

References

Zafeiriou DI. Primitive reflexes and postural reactions in the neurodevelopmental examination. Pediatr Neurol. 2004; 31(1): 1-8.

Bear LM. Early identification of infants at risk for developmental disabilities. Pediatr Clin North Am. 2004; 51(3): 685-701.

Review Date:11/9/2007
Reviewed By:Deirdre O’Reilly, M.D., M.P.H., Neonatologist, Division of Newborn Medicine, Children’s Hospital Boston and Instructor in Pediatrics, Harvard Medical School, Boston, Massachusetts.

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