Primitive Reflexes in Infants

I hope that by now you know that I am not a proponent of the phrase “Kids aren’t little adults,” preferring to focus on ensuring we are all empowered to learn and recognize the variance in anatomy and physiology in children compared to adults. Part of that empowerment is, of course, learning about those differences. Some are critically important and may impact acute care, like understanding how children are prone to have rapid oxygen desaturations. Others may be more “routine,” but can also impact the care we deliver in the Emergency Department. For instance, Developmental Milestones may not seem to be “critical,” life-saving components of assessments, but they clearly affect how we evaluate potential accidental injuries. Similarly, Infant Growth is important to weigh (see what I did there?) when determining the likelihood of problems that may lead to failure to thrive. Let’s look at another attribute that children have that may cause some of us to be perplexed at 3:00am – Primitive Reflexes in Infants:

Primitive Reflexes in Infants: Why They Matter

  • Primitive Reflexes can help asses the Central Nervous System in a newborn and infant. [Allen, 1986]
    • They are brain-stem mediated.
    • They are complex automatic movement patterns (really not “reflexes”) that are present at or near birth in health full-term infants.
    • They often become difficult to elicit once the child has voluntary motor control.
  • Pathology may be indicated by: [Allen, 1986]
    • The absence of the reflex when it would be expected.
    • The persistence of the reflex when it should have subsided.
  • Premature infants may have primitive reflexes that develop after their birth (based on their respective gestational age). [Allen, 1986]
    • In utero some of the reflexes can be witnessed via ultrasound! (super cool!)
    • The development of the reflexes can be used as markers of the maturation of the infant.

Primitive Reflexes in Infants: Some to Know

Rooting and Sucking Reflexes [Salandy, 2019]
  • For Rooting Reflex, the examiner touches one cheek or side of the mouth.
    • Normal response = the infant turns toward the stimulus.
  • For Sucking Reflex, the examiner places a gloved finger in the commissure of the infant’s mouth.
    • Normal response = the infant strongly latches onto finger.
  • Present at birth (may be delayed in premature infants)
  • Dissipate by ~4 months of age (although often seen until ~8 months in sleeping infants).
  • Abnormal responses may indicate problem with the trigeminal or hypoglossal nerve tracts.
Moro Reflex [Salandy, 2019; Futagi, 2012]
  • Also referred to as the “Startle Reflex.”
  • Elicited by several methods:
    • Sudden, loud noise
    • Sensation of falling (abrupt loss of support of the head and trunk)
    • Extending the infant’s arms followed by sudden release
    • Lifting the infant’s head and shoulders and carefully allow the head to drop relative to the body (this is most reliable method).
  • Normal response:
    • All four limbs aBduct and extend, then subsequently relax, adduct, and flex.
    • They may also extend the spine.
    • They can also close their fingers.
    • It should be symmetric!
  • The reflex typically remains up to 4 months of age, but can persist to 6 months of age.
    • Persistent findings may not be Moro reflex, but may be instead a sign of problems like Infantile Spasm.
    • Hyperactive response may also be seen as abnormal – it is seen as a feature of Neonatal Opiate Withdrawal syndrome.
    • Other disorders, like cerebral palsy, have altered onset and disappearance of Moro Reflex.
    • An asymmetric response is usually a sign of local injury.
Palmar and Plantar Grasp Reflexes [Salandy, 2019; Futagi, 2012]
  • Elicited by placing examiner’s finger into the palm or the sole and applying gentle pressure.
    • Appropriate response is for the digits to grasp AND hold.
    • One of my favorites!! Nothing like a tiny hand grasping onto your finger!! Life-Affirming!
  • Palmar Grasp:
    • Typically present at birth (by 28 weeks gestation age).
    • May be weak or absent in patients with injury to the nerves of the arm.
    • The reflex disappears at 6 months of age.
  • Plantar Grasp:
    • Similarly present at birth.
    • Disappears at 15 months of age.
Babinski Reflex [Salandy, 2019]
  • Often thought of being ABnormal in older children and adults, but it is a normal finding in infants.
    • A “normal response” is NO response or plantar (downward) flexion of the toes.
    • In infants, because their brain is immature, they have a POSITIVE Babinski NORMALLY.
  • It is elicited by applying lateral pressure on the plantar surface moving from heel to toes, curving toward the base of the 1st metatarsal.
  • In infants up to the age of 1 – 2 years of age, the normal response is a POSITIVE Babinski.
  • If absent in infants this age, it is ABnormal.
  • After 2 years of age, the presence of a Positive Babinski reflex is ABnormal and concerning for upper motor neuron disorder.
Stepping and Placing Reflexes [Salandy, 2019]
  • The Stepping Reflex is elicited by holding child in upright position, slightly leaning forward and with knees bent allowing the feet to touch a surface.
    • Appropriate response will be that the infant raises leg and then the other as if taking steps.
    • This is present during first 6 weeks of life.
    • It disappears by 2 months of life and then not present again until end of first year of life.
  • The Placing Reflex is elicited by holding the child in a similar position as was done for the Stepping Reflex, but the dorsum of the foot is touched by the edge of a surface/table.
    • Appropriate response is seen when the infant lifts the left to place the foot on the top of the surface.
    • This reflex diminished by the end of the 1st year of life.
    • Children with motor deficits may have a persistent reflex.
Asymmetric Tonic Neck Reflex [Salandy, 2019]
  • Also referred to as the “Fencing Reflex.”
  • This is elicited while the patient is in the supine position.
  • Turning the head leftward or rightward for 15 seconds will cause:
    • The arm and leg of the side turned towards to EXTEND
    • The arm and leg of the opposite side (looking away from) to FLEX
  • Reflex diminished by the 4th – 6th month of life.
  • Recurrence later may indicate decerebrate or decorticate posturing.

Moral of the Morsel

  • Neuro exam is more than “moves all extremities.” In the infant, you get good information about their neuro exam through these Primitive Reflexes.
  • Timing is everything! The Primitive Reflexes, especially the Moro, may cause parents to be alarmed. It is important to know when you need to be alarmed.



Sean M. Fox
Sean M. Fox
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