A newborn placed face-down will turn their head. Stroke the corner of their mouth and they will turn toward it. Startle them and their arms fling wide, then come back toward the body. These reflexes look like purposeful movements to parents but are automatic responses encoded in the lower brainstem and spinal cord, present before conscious control of movement is established.
They are not curiosities. They are clinical tools: the pattern and timing of primitive reflexes is one of the ways clinicians assess neurological development in the first months of life. Some parents are told their baby's reflexes are checked at a routine appointment without knowing why.
Healthbooq (healthbooq.com) covers newborn development and the assessments that happen in the first months of life.
Why Primitive Reflexes Exist
Primitive reflexes are mediated by subcortical brain structures (brainstem and spinal cord) rather than the cortex, which is relatively undeveloped at birth. They emerge during fetal development and are present at birth in healthy term infants.
As the cortex matures over the first months of life, it takes over motor control and the primitive reflexes are integrated or suppressed. A reflex that persists beyond its expected timeframe indicates that the cortex is not developing the inhibitory control it should, which can be a sign of neurological difficulty.
The timing of disappearance is therefore as clinically important as the timing of appearance.
Key Primitive Reflexes
The Moro reflex (startle reflex) is triggered by a sudden change in position or a loud noise. The arms extend and abduct (fling wide), the fingers spread, then the arms come back toward the midline. It is present from birth and integrates at around four to six months. An asymmetric Moro, where one arm extends less than the other, may indicate weakness on one side, such as a fractured clavicle or brachial plexus injury from birth.
The rooting reflex occurs when the corner of the mouth or cheek is stroked: the baby turns the head toward the stimulus and opens the mouth, ready to feed. It is present from birth and supports breastfeeding. It integrates at around three to four months as voluntary head control develops.
The sucking reflex is triggered by placing something in the baby's mouth. It is vigorous in healthy term infants and may be weak in premature or unwell babies. It integrates later in the first year.
The palmar grasp reflex occurs when something is placed in the baby's palm: the fingers close around it and grip firmly. It is present from birth and integrates at around five to six months, replaced by voluntary reaching and grasping.
The plantar grasp occurs when the sole of the foot is pressed: the toes curl downward to grip. It integrates at around nine to twelve months.
The stepping reflex occurs when a newborn is held upright with feet touching a firm surface: the legs make walking movements. It is present from birth and disappears at around two months before re-emerging as voluntary walking much later.
The Babinski reflex: when the sole of the foot is stroked from heel to toe, the big toe extends upward and the other toes fan out. This is normal in infancy and integrates at around twelve months. After twelve to eighteen months, a Babinski sign becomes abnormal and indicates upper motor neuron pathology.
The tonic neck reflex (ATNR or fencer reflex) occurs when the head is turned to one side: the arm on the face side extends while the arm on the skull side bends at the elbow. It is typically present from birth to around three to four months. Persistence beyond four to six months can interfere with motor development.
Clinical Assessment
Primitive reflexes are assessed at the newborn examination performed within the first 72 hours after birth, and again at the six-to-eight-week check. The midwife or GP checks for their presence and any asymmetry.
The key assessments in the newborn exam include the Moro (for symmetry and vigor), palmar grasp, rooting and sucking (relevant to feeding), and the Babinski. Absence of a reflex or significant asymmetry may indicate neurological, musculoskeletal, or birth injury that needs further assessment.
Parents who notice that their baby seems to have a reflex that is persisting beyond the expected timeframe, or who see an asymmetric response, can raise this at a health visitor appointment.
Key Takeaways
Newborn reflexes are involuntary motor responses present at birth that reflect normal neurological function and have specific developmental timelines for when they should be present and when they should disappear. The absence of a reflex at the appropriate time, or the persistence of a reflex beyond its expected disappearance, can indicate neurological problems and is assessed by clinicians at routine checks. The Moro (startle), rooting, sucking, grasp, stepping, and Babinski reflexes are among the most clinically important. Some reflexes are protective; others are thought to be evolutionary remnants. All are replaced by voluntary, controlled movements as the cortex matures.
