Moro reflex

The Moro reflex is an infantile reflex that develops between 28 and 32 weeks of gestation and disappears at 3–6 months of age. It is a response to a sudden loss of support and involves three distinct components:[1]

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

It is distinct from the startle reflex.[2] Unlike the startle reflex, the Moro reflex does not decrease with repeated stimulation.[3] The primary significance of the Moro reflex is in evaluating integration of the central nervous system.[4][5]

Eliciting the Moro reflex

Ernst Moro elicited the Moro reflex by slapping the pillow on both sides of the infant's head. Other methods have been used since then, including rapidly lowering the infant (while supported) to a sudden stop and pinching the skin of the abdomen. Today, the most common method is the head drop, where the infant is supported in both hands and tilted suddenly so the head is a few centimeters lower than the level of the body.[3]

Clinical significance

The Moro reflex may be observed in incomplete form in premature birth after the 25th week of gestation, and is usually present in complete form by week 30 (third trimester).[1] Absence or asymmetry of either abduction or adduction by 2 to 3 months age can be regarded as abnormal, as can persistence of the reflex in infants older than 6 months.[3] Furthermore, absence during the neonatal period may warrant assessment for the possibility of developmental complications such as birth injury or interference with brain formation.[3] Asymmetry of the Moro reflex is especially useful to note, as it is almost always a feature of root, plexus, or nerve disease.[6]

The Moro reflex is impaired or absent in infants with kernicterus.[7]

An exaggerated Moro reflex can be seen in infants with severe brain damage that occurred in-utero, including microcephaly and hydranencephaly.[8] Exaggeration of the Moro reflex, either due to low threshold or excessive clutching, often occurs in newborns with moderate hypoxic-ischemic encephalopathy.[9] The Moro reflex is also exaggerated in infants withdrawing from narcotics.[10]

Persistence of the Moro reflex beyond 6 months of age is noted only in infants with severe neurological defects, including cerebral palsy.[11][12]

History

The Moro reflex was first described in western medicine by Austrian pediatrician Ernst Moro (1874–1951) in 1918. Moro referred to it as the Umklammerungsreflex (embracing reflex).[13] In this publication, he 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". According to him, this reflex should disappear after the infant's first 3–6 months of life. Since then, the Moro reflex has been used to detect early neurological problems in infants.[13] Absence or prolonged retention of Moro reflex can be signs that the infants need neurological attention.[14]

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.[15]

References
  1. Edwards, Christopher W.; Al Khalili, Yasir (2019), "Moro Reflex", StatPearls, StatPearls Publishing, PMID 31194330, retrieved 2019-08-06
  2. Fletcher, Mary Ann (1998). Physical Diagnosis in Neonatology. Philadelphia: Lippincott-Raven. p. 472. ISBN 978-0397513864. Retrieved 7 February 2013.
  3. Suzuki, Yasuhiro; Toribe, Yasuhisa; Futagi, Yasuyuki (2012). "The Grasp Reflex and Moro Reflex in Infants: Hierarchy of Primitive Reflex Responses". International Journal of Pediatrics. 2012: 191562. doi:10.1155/2012/191562. PMC 3384944. PMID 22778756.
  4. "179 Neonatal Neurology". Springer Reference. SpringerReference. Springer-Verlag. 2011. doi:10.1007/springerreference_226504.
  5. Suzuki, Yasuhiro; Toribe, Yasuhisa; Futagi, Yasuyuki (2012). "The Grasp Reflex and Moro Reflex in Infants: Hierarchy of Primitive Reflex Responses". International Journal of Pediatrics. 2012: 191562. doi:10.1155/2012/191562. PMC 3384944. PMID 22778756.
  6. Volpe, Joseph J. (2008). Neurology of the newborn. Major Problems in Clinical Pediatrics. Vol. 22. Saunders/Elsevier. pp. 1–648. ISBN 9781416039952. OCLC 878742566. PMID 7022034.
  7. "Kernicterus". NORD (National Organization for Rare Disorders). Retrieved 2019-08-06.
  8. Multiple authors. "Moro Reflex - an overview". ScienceDirect Topics. Retrieved 2019-08-01.
  9. "179 Neonatal Neurology". Springer Reference. SpringerReference. Springer-Verlag. 2011. doi:10.1007/springerreference_226504.
  10. Chasnoff, Ira J.; Burns, William J. (1984). "The Moro Reaction: A Scoring System for Neonatal Narcotic Withdrawal". Developmental Medicine & Child Neurology. 26 (4): 484–489. doi:10.1111/j.1469-8749.1984.tb04475.x. ISSN 1469-8749. PMID 6479468. S2CID 36440317.
  11. Samuels, Martin A.; Ropper, Allan H. (2009). "Normal Development and Deviations in Development of the Nervous System". Adams and Victor's Principles of Neurology (9th ed.). New York: McGraw-Hill Medical. ISBN 9780071499927. Retrieved 7 February 2013.
  12. Agarwal, Anil; Verma, Indreshwar (December 2012). "Cerebral palsy in children: An overview". Journal of Clinical Orthopaedics and Trauma. 3 (2): 77–81. doi:10.1016/j.jcot.2012.09.001. PMC 3872805. PMID 26403442.
  13. Weirich, Angela; Hoffmann, Georg F. (2005-10-01). "Ernst Moro (1874–1951)—A great pediatric career started at the rise of university-based pediatric research but was curtailed in the shadows of Nazi laws". European Journal of Pediatrics. 164 (10): 599–606. doi:10.1007/s00431-005-1703-2. ISSN 1432-1076. PMID 15931526. S2CID 27343540.
  14. Edwards, Christopher W.; Al Khalili, Yasir (2019), "Moro Reflex", StatPearls, StatPearls Publishing, PMID 31194330, retrieved 2019-08-01
  15. Berk, Laura E. (2009). Child Development (8th ed.). Boston: Pearson. ISBN 978-0-205-61559-9. Retrieved 7 February 2013.
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