Reflexes are involuntary, i.e. unintentional, responses of the body to stimulation. They indicate a state of health within normality. There are a variety of primary reflexes, which appear at birth.

In this article we will know one of them, the Moro reflex , a reflex that is observed at birth, and that usually disappears after 3 or 4 months. Its persistence or absence usually indicates abnormalities or alterations in development.

Related article: “The 12 Primitive Reflexes of Babies”

Origin of the Moro reflex

Moro’s reflex, also called “baby’s startle reflex”, is a primary reflex named after the Austrian pediatrician Ernst Moro , who first described it in Western medicine. Its presence in the indicated period indicates normal development in the newborn, and the presence of health.

Ernst Moro (1874 – 1951) was an Austrian physician and pediatrician who studied medicine in Graz, Austria, and who obtained his master’s degree in medicine in 1899. As we have seen, he not only described Moro’s reflex for the first time, but discovered it and gave it a name.

When does he show up?

When a baby is born, the hospital checks for some important primary reflexes, including the Moro reflex.

The Moro reflex is observed completely in newborn babies , who are born after the 34th week of pregnancy, and incompletely in those born from a preterm birth from the 28th week.

This reflex extends to 3 or 4 months of age. Its absence or persistence may indicate neurological defects or alterations of the nervous system . During the first 4 months, the paediatrician will continue to check during the visits if the child still has the reflex. Even beyond these months, because, as we will see in detail later on, the persistence of the reflex beyond 4 or 5 months may indicate certain neurological defects.

What is it?

To see how the Moro reflex appears, the baby should be placed on his or her back on a soft, padded surface. Gently lift the baby’s head with enough support and begin to take the weight off the cushion. That is, the baby’s body is not lifted off the cushion, only the weight is removed. Then the head is released suddenly, allowed to fall backwards momentarily , but held up again quickly, not allowing it to hit the padded surface.

The baby will usually respond with a startled look; his arms will move to the side with palms up and thumbs flexed. The baby will probably even cry for a minute.

In other words, the Moro reflex appears when the baby feels a lack of support (it can also appear when there is a sudden change in position). When the Moro reflex ends, it does so in this way; the baby retracts its arms towards the body, with elbows bent, and finally relaxes.

Alterations

The absence or persistence of the Moro reflex indicates certain alterations in normal development:

1. Absence of reflex

The absence of the Moro reflex in an infant is abnormal, and may suggest, for example, damage to the brain or spinal cord . On the other hand, if it occurs on only one side, there is a possibility of a fractured clavicle or damage to the brachial plexus nerve group.

2. Persistence of reflex

If the Moro reflex persists beyond the fourth or fifth month of age, it may also indicate severe neurological defects. This is why its existence is still checked at the pediatrician’s office.

Its phases

But what does Moro’s reflex mean in the context of an integrated assessment of the central nervous system? Let us first see the components involved in the reflex :

  • The startle reflex.
  • The movement of the arms in abduction.
  • The movement of the arms in adduction.
  • Usually the crying.

Thus, the absence of these components (except for crying) or an asymmetry in movements is not normal. Nor is the persistence of these components in children and adolescents a good sign .

On the other hand, some people with cerebral palsy may have a persistent and exacerbated Moro reflex. As we have seen, abnormalities in its manifestation indicate brain or spinal cord disorders.

Altered reflex syndromes

Some of the syndromes with an abnormal Moro reflex are Erb-Duchenne paralysis (upper brachial plexus paralysis); this is a course with an asymmetric Moro reflex, caused by shoulder dystocia.

Another syndrome, this time with an absent Moro reflex, is DeMorsier syndrome, which includes optic nerve dysplasia . This syndrome is characterized by the absence of the reflex as part of specific complications unrelated to the shoulder and its nerves.

Finally, the absence of the Moro reflex is also detected in newborns with Down syndrome and in newborns with perinatal listeriosis . The latter consists of an infrequent infection, related to the ingestion of contaminated food, which can have serious consequences for the mother and the newborn.

Bibliographic references:

  • García Madruga, J.A.; Deval, J. (2010). Developmental Psychology I. Cognitive and linguistic development. UNED. Madrid
  • MedlinePlus. (2019). Moro Reflection. Medical encyclopedia.
  • Paris, E. (2014). The Moro or startle reflex in the baby. Babies and more.