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Maternal Newborn Health
문제

A nurse is assessing a 2-day-old newborn's primitive reflexes. Which finding would indicate a normal Moro reflex response?

해설
The Moro reflex is elicited by startling the newborn; normal response involves extension/abduction of arms and legs followed by adduction to midline. Other options describe rooting (1), Babinski (2), and grasp (3) reflexes.
같은 주제 다음 문제A nurse is assessing a 2-day-old newborn's primitive reflexes. Which finding would indicat…

심화 해설

Understanding the Moro Reflex
The Moro reflex, often called the "startle reflex," is one of the most critical primitive reflexes assessed in a newborn. It is an involuntary, brainstem-mediated response that provides a window into the integrity of the infant's central nervous system. Primitive reflexes like the Moro are fully established in term newborns and are expected to be symmetrical and complete [1]. The reflex is typically elicited by a sudden change in the infant's position, such as a slight head drop relative to the trunk, or a loud noise, which simulates a falling sensation.

Analyzing the Correct Response
The correct finding, described in option 4, is the classic sequence of the Moro reflex. When startled, the newborn will first symmetrically extend and abduct the arms, spreading the fingers, and then bring the arms back to the midline in an adduction movement, often followed by a cry. This two-phase response (extension/abduction followed by flexion/adduction) is the hallmark of a normal, intact Moro reflex.

Differentiating Other Primitive Reflexes
The incorrect options describe other important primitive reflexes, and it is crucial to distinguish between them for a comprehensive neurological assessment:

- Option 1 (Rooting Reflex): The turning of the head toward a cheek stimulus is the rooting reflex, which facilitates feeding by helping the newborn locate the nipple [1]. It is not part of the Moro response.
- Option 2 (Babinski Reflex): The fanning of the toes when the sole of the foot is stroked is the Babinski reflex. This is a normal finding in infants up to about 12-24 months of age, after which it is inhibited by the maturing corticospinal tract.
- Option 3 (Palmar Grasp Reflex): The grasping of a finger placed in the palm is the palmar grasp reflex. This reflex is strong enough that the infant can briefly support their own weight.

Clinical Significance and Developmental Trajectory
The presence of a normal Moro reflex confirms the functional integrity of the brainstem and motor pathways. An asymmetrical response, where one arm moves differently than the other, can indicate a peripheral nerve injury (like Erb's palsy) or a clavicle fracture. An absent or incomplete response may suggest significant central nervous system depression or injury. The Moro reflex is expected to be inhibited and disappear between 4 and 6 months of age as the cerebral cortex matures and voluntary motor control develops [1]. The persistence of this reflex beyond this developmental window, known as a retained primitive reflex, is not a benign finding. It can be a potential biomarker for neurodevelopmental conditions, signaling a functional disconnectivity related to cortical maturation delays . The hierarchical inhibitory control from higher cortical centers fails to integrate the reflex, which can be observed in conditions such as attention-deficit/hyperactivity disorder, developmental coordination difficulties, and sensory-processing-related presentations .
References (research sources)
  • [1]
    Primitive Reflexes: Comprehensive Neurological Assessment Across the LifespanResearch articleChamarthi VS, Gunasekaran V, Daley SF. (2026)

임상 시나리오

Clinical Assessment of the Moro Reflex
Elicitation Technique
  • Support the newborn in a semi-sitting position with one hand behind the head and back.
  • Allow the head to drop back approximately 1-2 cm relative to the trunk, ensuring the head is caught safely.
  • Alternatively, create a loud noise or jar the bassinet, though the head-drop method is most controlled.
Normal Response
  • Phase 1: Symmetrical arm extension and abduction with fingers spread.
  • Phase 2: Arms return to midline in flexion and adduction, often with a cry.
  • Response should be complete, bilaterally equal, and appear by 28-32 weeks gestation, fully present at term.
Abnormal Findings
  • Asymmetrical response: May indicate brachial plexus injury (e.g., Erb's palsy), clavicle fracture, or hemiparesis.
  • Absent response: Suggests severe CNS depression, brainstem dysfunction, or significant prematurity.
  • Exaggerated or persistent reflex: Beyond 4-6 months may indicate hyperreflexia or neurological impairment.
Nursing Considerations
  • Perform the reflex assessment when the newborn is quiet but alert for optimal observation.
  • Ensure a safe environment; never let the head drop unsupported.
  • Document symmetry, completeness, and any distress; report abnormalities promptly.
  • Educate parents that the Moro reflex disappears around 4-6 months as voluntary motor control develops.

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