The Moro reflex is an

infantile reflex Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants, but not neurologically intact adults, in response to particular stimuli. These reflexes are suppressed by the development of the ...

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: # spreading out the

arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...

s ( abduction) # pulling the arms in (

adduction Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

) #

crying Crying is the dropping of tears (or welling of tears in the eyes) in response to an emotional state, or pain. Emotions that can lead to crying include sadness, anger, and even happiness. The act of crying has been defined as "a complex secr ...

(usually) It is distinct from the startle reflex. Unlike the startle reflex, 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 central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

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.

Clinical significance

The Moro reflex may be observed in incomplete form in

premature birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 2 ...

after the 25th week of gestation, and is usually present in complete form by week 30 (

third trimester Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but can ...

). 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. Furthermore, absence during the neonatal period may warrant assessment for the possibility of developmental complications such as birth injury or interference with brain formation. Asymmetry of the Moro reflex is especially useful to note, as it is almost always a feature of root,

plexus In neuroanatomy, a plexus (from the Latin term for "braid") is a branching network of vessels or nerves. The vessels may be blood vessels (veins, capillaries) or lymphatic vessels. The nerves are typically axons outside the central nervous syste ...

, or nerve disease. The Moro reflex is impaired or absent in infants with

kernicterus Kernicterus is a bilirubin-induced brain dysfunction. The term was coined in 1904 by Christian Georg Schmorl. Bilirubin is a naturally occurring substance in the body of humans and many other animals, but it is neurotoxic when its concentratio ...

. An exaggerated Moro reflex can be seen in infants with severe brain damage that occurred in-utero, including

microcephaly Microcephaly (from New Latin ''microcephalia'', from Ancient Greek μικρός ''mikrós'' "small" and κεφαλή ''kephalé'' "head") is a medical condition involving a smaller-than-normal head. Microcephaly may be present at birth or it ...

and

hydranencephaly Hydranencephaly is a condition in which the brain's cerebral hemispheres are absent to a great degree and the remaining cranial cavity is filled with cerebrospinal fluid. "Cephalic" is the scientific term for "head" or "head end of body". Hydrane ...

. Exaggeration of the Moro reflex, either due to 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

cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sens ...

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). 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. 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.

References

External links

Medline Plus

Pathologic Moro Reflex in an adult following acute demyelinating lesion of unknown origin in the medulla oblongata (Neurology)
{{Primitive_reflexes Reflexes Obstetrics Neonatology Articles containing video clips