Moro Reflex: Characteristics And Clinical Implications In Infants

This is one of the primary reflexes that manifest in healthy newborn babies.

Moro reflex

Reflexes are involuntary responses of the body to stimulation, that is, unintended. These indicate a state of health within normality. There is a great variety of primary reflexes, which appear at birth.

In this article we will know one of them, the Moor reflex, a reflex that is observed at birth, and that generally 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

The Moro reflex, also called “baby startle”, is a primary reflex that owes its name to the Austrian pediatrician Ernst Moro, who was the first to describe it in Western medicine. Its presence in the indicated period indicates a 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 obtained his master’s of medicine in 1899. As we have seen, he not only described Moro’s reflex for the first time, he also described it discovered and named it.

When does it appear?

When a baby is born, the hospital is found to have some important primary reflexes, including the Moor reflex.

The Moro reflex is fully observed in newborn babies, who are born after the 34th week of pregnancy, and incompletely in those born from premature delivery after the 28th week.

This reflex lasts until 3 or 4 months of life. Its absence or persistence may indicate neurological defects or alterations of the nervous system. During the first 4 months, the pediatrician will continue to check in the visits if the child continues to have the reflex. Even beyond these months, because, as we will see in detail later, the persistence of the reflex beyond 4 or 5 months can indicate certain neurological defects.

What does it consist of?

To see how the Moro reflex appears, the baby should be placed on his back on a soft, padded surface. The baby’s head is lifted gently with sufficient support and the weight of the cushion begins to be removed; that is, the baby’s body does not lift off the cushion, only the weight is removed. Then his head is suddenly released, he falls back momentarily, but is quickly held on again, not allowing him to hit the padded surface.

The normal thing then is that the baby responds with a startled look; Your arms will move to the sides with your palms up and your thumbs flexed. The baby may even cry for a minute.

That is, the Moro reflex appears when the baby feels a lack of support (it can also appear in the event of a sudden change in position). When Moro’s reflex ends, he does it this way; the baby draws his arms towards the body, with the elbows bent, and finally relaxes.


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 a baby is abnormal, and may suggest, for example, damage to the brain or spinal cord. On the other hand, if it occurs only on one side, there is the possibility of a fractured clavicle or damage to the group of nerves of the brachial plexus.

2. Persistence of the 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 continues to be verified in pediatrician consultations.

Its phases

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

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

Thus, the absence of these components (except 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 the Moro reflex persistently and exacerbated. As we have seen, abnormalities in their manifestation indicate disorders of the brain or spinal cord.

Syndromes with impaired reflex

Some of the syndromes with an abnormal Moro reflex are Erb-Duchenne palsy (upper brachial plexus palsy); This presents 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 occurs with the absence of the reflex as part of specific complications not related 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 and that can have serious consequences for the mother and the newborn.

Bibliographic references:

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

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