Moro reflex

The Moro reflex is an infantile reflex that develops between 25–30 weeks of gestation and disappears between 3–6 months of age. It is a response to a sudden loss of support and involves three distinct components:

1. Spreading of the arms (abduction)
2. Pulling the arms in (adduction)
3. Crying (usually)

It is distinct from the startle reflex, which diminishes with repeated stimulation.

Eliciting the Moro Reflex

Moro reflex while sleeping

The Moro reflex can be elicited using different techniques:

• Classic Method – Originally described by Ernst Moro, where the examiner slaps both sides of the pillow near the infant’s head.
• Head Drop Method – The most common method, where the infant is supported and suddenly tilted downward, lowering the head a few centimeters below body level.
• Sudden Movement or Sound – A rapid descent while supporting the infant or an unexpected loud noise may trigger the reflex.

Clinical Significance

The Moro reflex is important for assessing neurological development in infants. It is observed in the third trimester and should disappear by 6 months.

Abnormal Responses

Absence or asymmetry of the reflex may indicate:

• Birth trauma (e.g., brachial plexus injury)
• Neonatal brain injury
• Congenital neurological conditions (e.g., cerebral palsy)

Exaggerated Moro reflex can occur in:

• Hypoxic-ischemic encephalopathy (HIE)
• Neonatal drug withdrawal syndrome (e.g., narcotic withdrawal)
• Microcephaly or brain malformations (e.g., hydranencephaly)

Persistence Beyond 6 Months

A persistent Moro reflex beyond 6 months is seen in infants with:

• Severe neurological conditions (e.g., cerebral palsy)
• Delayed myelination
• Neonatal hypoxia

History

The Moro reflex was first described in 1918 by Ernst Moro (1874–1951), an Austrian pediatrician. He initially referred to it as the Umklammerungsreflex (embracing reflex). His original description stated:

• "When a young infant is placed on the examination table and one taps with hands on both sides of the pillow, there follows a rapid symmetrical extending abduction of both extremities, which approach each other in adduction immediately thereafter".*

Since then, the Moro reflex has been widely used to assess early neurological development.

Evolutionary Function

The Moro reflex is believed to be a vestigial survival mechanism. In primates, it may have functioned to help infants cling to their mothers when startled. If the infant lost balance, the sudden movement would trigger the reflex, causing the baby to grasp the mother’s body for protection.

Related Reflexes

The Moro reflex is part of a group of primitive reflexes, which include:

• Rooting reflex – Helps infants find the nipple for feeding.
• Palmar grasp reflex – Causes infants to grip an object placed in their hand.
• Tonic neck reflex – Also known as the "fencing reflex".