thumbtime=6|thumb|The Moro reflex in a four-day-old infant: 1) the reflex is initiated by pulling the infant up from the floor and then releasing him; 2) he spreads his arms; 3) he pulls his arms in; 4) he cries (10 seconds)

thumb|Moro reflex while sleeping

The Moro reflex is an infantile reflex that develops by 32 weeks of gestation and disappears at the sixth month of age. It is a response to a sudden loss of support and involves three distinct components:

  1. spreading out the arms (abduction)
  2. pulling the arms in (adduction)
  3. crying (usually)

It is distinct from the startle response. Unlike the startle response, the Moro reflex does not decrease with repeated stimulation. The primary significance of the Moro reflex is in evaluating integration of the central nervous system.

The Moro reflex is impaired or absent in infants with kernicterus. An exaggerated Moro reflex can be seen in infants with severe brain damage that occurred in-utero, including microcephaly and hydranencephaly. Exaggeration of the Moro reflex, manifesting either as low threshold or excessive clutching, often occurs in newborns with moderate hypoxic-ischemic encephalopathy. The Moro reflex is also exaggerated in infants withdrawing from narcotics. Persistence of the Moro reflex beyond 6 months of age is noted only in infants with severe neurological defects, including autism and cerebral palsy.

History

The Moro reflex was first described in western medicine by pediatrician Ernst Moro (1874–1951) in 1918. Moro referred to it as the Umklammerungsreflex (embracing reflex). Absence or prolonged retention of Moro reflex can be signs that the infants need neurological attention.

Function

The Moro reflex may be a survival instinct to help the infant cling to its mother. If the infant lost its balance, the reflex caused the infant to embrace its mother and regain its hold on the mother's body. The Moro reflex might also be an alarm signal from the baby who is about to lose support, and the spread arms provide extremities for where to be grabbed by its handler to prevent a fall.

See also

  • Primitive reflexes

References

  • Pattnaik P, Al Khalili Y. Moro Reflex. [Updated 2025 Aug 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK542173/