From the Guidelines
The Moro reflex typically disappears between 3 to 6 months of age in healthy infants. This primitive reflex, also known as the startle reflex, is present at birth and involves the baby symmetrically extending their arms outward with fingers spread when startled, followed by bringing the arms back to the center of the body. The disappearance of this reflex is an important developmental milestone that indicates normal neurological maturation of the infant's central nervous system.
As noted in the study on neonatal drug withdrawal 1, the Moro reflex is mentioned as one of the neurologic excitability signs in infants experiencing withdrawal, but it does not provide specific information on when the Moro reflex typically disappears in healthy infants. However, based on general medical knowledge, if the Moro reflex persists beyond 6 months, it may warrant discussion with a pediatrician as persistence could potentially indicate neurological concerns.
Key points to consider:
- The Moro reflex is a normal reflex present at birth
- It typically disappears between 3 to 6 months of age
- Persistence beyond 6 months may indicate neurological concerns
- An asymmetrical Moro reflex at any age might suggest injury to the brachial plexus, clavicle, or humerus and should be evaluated promptly.
It's essential for parents to understand that this reflex is completely normal in newborns and young infants, and its gradual fading is part of expected development as the brain matures and gains more control over reflexive movements.
From the Research
Moro Reflex Disappearance
- The Moro reflex is a primitive reflex that disappears after the first three months of life 2.
- This reflex is present in newborns and is characterized by a specific sequence of movements, including extension-adduction of both arms, orientation of the body, head, and eyes towards a human person, and full extension-abduction of both arms with spreading of the fingers, crying, and a distressed face 3.
- The disappearance of the Moro reflex is due to the inhibition of the archaic neural circuit present in the newborn by the upper brain structures 2.
Neural Mechanism
- The neural centre underlying the Moro reflex is located in the lower part of the brainstem, specifically in the pons to the medulla 2, 4.
- The Moro reflex is thought to involve the activation of an archaic neural circuit present in the newborn, which is later inhibited by the upper brain structures 2.
- The neural mechanism of the Moro reaction probably involves both the fear and the separation-distress systems 3.
Clinical Significance
- The absence of the Moro reflex during the neonatal period and early infancy is highly diagnostic, indicating a variety of compromised conditions 4.
- The Moro reflex has been linked to epileptic spasms and generalized tonic-clonic seizures, which may be due to the pathological activation of the same neural archaic circuit involved in the genesis of the Moro reflex 2.