Moro Reflex

Historical Overview

• Ernst Moro first described the Moro reflex in 1918. Moro noticed that when a baby was placed supine on a changing mat and both sides of the mat were struck, both of the baby’s arms would jump apart symmetrically, then close in slightly tonic shaped arc movements. Similar arm movements were observed during head dropping in infants aged from a few hours to 3 months old in the supine position, as well as after other stimuli, such as after changing a diaper, the emitting of a sudden noise, hitting the abdomen, blowing a puff of air on the face, or applying hot or cold water on the abdomen.^1,2
• Moro proposed the name “Umklammerungreflex” (embracing or clasping reflex), which went on to become known as the Moro reflex.²

Description

• The Moro reflex a primitive infantile reflex that is widely tested for in newborn examinations to assess the functioning of the central nervous system, most commonly using the head-drop method.³

Pathophysiology

• The Moro reflex is present as early as 28 weeks of gestation with hand opening, extension and abduction by 32 weeks and anterior flexion by 37 weeks of gestation. Absence, depressed or exaggeration of the reflex may indicate central nervous system disorders and asymmetria of the Moro reflex may be related to obstetrical damage of plexus or nerve. Persistence of the primitive reflexes beyond 6 months interferes with developmental and neurological impairment. Preterm infants born between 25-34 weeks’ gestation often show several differences on this neurological examination at term, as they may be more hyperexcitable, have less flexor tone in the limbs, and have less extensor tone in the neck.⁴
• The initial phase of the Moro reflex comprises abduction of the upper limbs at the shoulders and extension of the forearms at the elbows, with slight extension of the spine and retraction of the head. The forearms are supinated and the digits extended, except for the semiflexed index fingers and thumbs, forming the shape of a “C”. There is sometimes a slight tremor or clonus-like rhythmic movements of the limbs. Subsequently the arms adduct at the shoulders and the forearms flex at the elbows: the upper limbs describe an arc-like movement, bringing the hands in front of the body, which finally return to the original position.²
• The neural center of the Moro reflex seems located in the lower part of the brain stem, as this reflex is present in anencephalic newborns. Vestibular stimulation seems to play a crucial role in triggering the Moro reflex because it has been obtained by fixing a child’s head and body on a table or tilting chair—to remove any proprioceptive stimulation of the neck—and in anencephalic infants, it was only obtained when the vestibular nuclei were preserved.²

Instructions

1. Although a number of methods have previously been used to elicit the Moro reflex, the head drop method is currently regarded as the method-of-choice
2. Infants should be tested while they are awake, but not crying
3. Hold the infant suspended horizontally in a symmetrical supine position, with one hand behind the chest and the other supporting the head, which should be held in a midline position
4. Release the infant’s head and allow it to drop back a few centimeters before quickly catching it again
5. The clinician should be sure to open both hands at the moment of elicitation, so as not to provoke an asymmetrical response
6. Observe the movement and position of the infant’s head, neck, and upper extremities

Variations

• “Drop of the baby” method: the infant is suspended horizontally, as in the head drop method, and then the examiner lowers his or her hands rapidly about 10-20 cm and brings them to an abrupt halt; there is no dorsiflexion of the neck with this technique.¹
• Other methods of elicitation used in the past include hitting a pillow on either side of an infant’s head with the hands (Moro’s original method), hitting on the table surface, warm or cold application to the chest or stomach, and a tap on the abdomen.¹

Related Signs and Tests

• Palmar grasp reflex
• Plantar grasp reflex
• Startle reflex
  • Sometimes used synonymously with the Moro reflex, but the startle reflex is more specifically a response to a sudden external stimulus, such as light, noise, or movement close to the face; while the vestibular, proprioceptive, and exteroceptive sensory pathways have all been implicated in the mechanism of the Moro reflex, the startle reflex involves auditory and visual pathways.³

Diagnostic Performance Characteristics

• The absence or diminution of the Moro reflex within 2-3 months of age and the persistence of the response beyond 6 months of age can be regarded as abnormal. The absence of the response during the neonatal period and early infancy is of especial clinical significance and may indicate a compromised condition or disorder.¹
• Asymmetry of the response is usually a sign of local injury, as damage to a peripheral nerve or cervical cord or a fracture of the clavicle may inhibit the reflex on the affected side.¹