What is the significance of assessing neonatal reflexes, such as rooting reflex, sucking reflex, Moro reflex, and tonic labyrinthine reflex, in a 3-month-old infant?

Assessment of Neonatal Reflexes in a 3-Month-Old Infant

At 3 months of age, most primitive reflexes should be diminishing or absent, and their persistence beyond expected timelines signals potential neuromotor dysfunction requiring further evaluation. 1

Expected Reflex Status at 3 Months

Reflexes That Should Be Absent or Nearly Absent

• The asymmetric tonic neck reflex (ATNR) should be completely absent by 4 months, making its presence at 3 months a concerning finding that warrants close monitoring, as persistence interferes with midline hand inspection and normal motor development 1
• The Moro reflex should be diminishing significantly by 3 months and should be absent or nearly absent by 6 months in healthy term infants 1, 2
• The palmar grasp reflex should be weakening at 3 months, with complete resolution expected by 6 months 1, 2

Reflexes Still Present at 3 Months

• Rooting and sucking reflexes may still be present at 3 months but should be assessed for quality and symmetry, as abnormalities can indicate neurological dysfunction 3
• The Babinski reflex remains normal at this age and persists beyond infancy 4

Clinical Significance of Assessment

Why Assessment Matters

Persistence of primitive reflexes beyond their expected disappearance timeline is strongly associated with cerebral palsy and developmental delays. 2 The combined examination of primitive reflexes serves as a simple but predictive screening test for early identification of infants at risk for neuromotor disorders 2.

• Infants with 5 or more abnormal postural reactions have been shown to develop either cerebral palsy or developmental retardation 2
• Asymmetric responses are particularly concerning, as they may indicate unilateral neurological pathology 2

Key Assessment Components at 3 Months

When examining a 3-month-old, the clinician should specifically evaluate:

• Moro reflex: Should be elicitable but weakening; persistence of an exaggerated response suggests CNS irritability (as seen in neonatal drug withdrawal) 3
• Rooting and sucking reflexes: Assess for presence, symmetry, and coordination; absent or weak responses indicate brainstem dysfunction 3
• ATNR: Should be minimal or absent; strong persistence at 3 months predicts motor delays 1, 2
• Muscle tone and postural control: Hypotonia or hypertonia at 3 months requires investigation for neuromuscular disorders 3
• Deep tendon reflexes: Hyperreflexia suggests upper motor neuron dysfunction, while diminished reflexes suggest lower motor neuron or muscle disease 3

Red Flags Requiring Immediate Evaluation

Any of the following findings at 3 months mandate prompt neurological assessment:

• Persistent strong ATNR that prevents midline activities 1
• Absent or asymmetric Moro reflex, which may indicate brachial plexus injury, hemiparesis, or CNS depression 3, 2
• Absent rooting or sucking reflexes, suggesting brainstem pathology 3
• Exaggerated reflexes with increased tone, indicating possible cerebral palsy 2
• Absent or diminished deep tendon reflexes with hypotonia, raising concern for neuromuscular disorders like spinal muscular atrophy 3

Special Populations

Premature Infants

• Corrected gestational age must be used when assessing primitive reflexes in former preterm infants 5
• Reflexes in premature infants follow postconceptional age, not chronological age, so a 3-month-old born at 32 weeks should be assessed as if they are 1 month old (corrected age) 5

High-Risk Infants

• Infants with history of NICU admission, birth asphyxia, or neonatal drug withdrawal show higher rates of abnormal or absent primitive reflexes 4
• These infants require more frequent developmental surveillance beyond routine well-child visits 4

Clinical Pitfalls to Avoid

• Do not dismiss persistent primitive reflexes as "normal variation" at 3 months; they predict motor and cognitive difficulties 2, 6
• Behavioral state affects reflex assessment: Infants must be in an appropriate state of alertness (not crying, not deeply asleep) for accurate evaluation 4
• Single assessment is insufficient: Serial examinations provide more reliable information about neuromotor trajectory 5
• Do not overlook subtle asymmetries, as they may be the earliest sign of hemiparetic cerebral palsy 2