Sensory processing
The Moro Reflex: What It Is, When It Fades, and What Persistence Means
The startle response every newborn has, why it disappears, and what a clinician is actually looking for when it does not.
- Expert Reviewed
- Evidence Based
- Patient Focused
The Moro reflex is the startle response present in every healthy newborn. A sudden change in head position, or a loud sound, produces a movement in two phases: the arms swing out and the fingers extend, then the arms draw back in toward the body. It can be seen from about 25 weeks post-conceptional age, is reliably present by 30 weeks, begins to fade by around 12 weeks after birth and has usually gone by 6 months.1 For a newborn, its ABSENCE is the more urgent finding, and an asymmetrical response usually points to a local injury rather than to the brain. Persistence past the expected window is worth raising with a doctor. On its own it is not a diagnosis, and it is not evidence that a reflex-integration program will change anything.
What the Moro reflex is
The Moro reflex — also called the startle reflex — is an involuntary, protective motor response to a sudden disruption of balance or to intense stimulation. It was first described by Ernst Moro in 1918.1
It runs in two phases. First the arms swing outward and extend, the fingers open, and the neck and spine extend slightly. Then the arms come back in, the hands move to the front of the body, and the arms return to the infant's sides.1
Why it exists. Like the other primitive reflexes, it does not require conscious control. It belongs to the period before higher brain centers take over voluntary movement.2
When it appears, and when it fades
| Point | What is expected1 |
|---|---|
| From about 25 weeks post-conceptional age | The reflex can first be observed. |
| By 30 weeks post-conceptional age | Typically present. |
| At term | Present in full-term infants. |
| By about 12 weeks after birth | Begins to disappear. |
| By 6 months | Usually gone completely. |
A second clinical reference gives the window as roughly 4 to 6 months, which is the same picture stated less precisely.2
How a clinician checks it
The reflex is elicited by a sudden change in head position or by a sudden loud sound — the point is the abruptness, not force. What the examiner watches for is the two-phase pattern, and whether both sides do the same thing.
Preterm infants show it differently. The response is weaker in preterm newborns than in full-term newborns at the same post-conceptual age, because of lower muscle tone, less resistance to passive movement and slower arm recoil.1 A weak response in a baby born early is not, on its own, the same finding as a weak response in a baby born at term.
When absence matters more than persistence
This is the part most often missed in parent-facing writing about retained reflexes: for a newborn, the reflex being missing is the more serious finding.
Findings that need a doctor, not a program
- Absent or gone too early. Can follow birth injury, severe asphyxia during birth, intracranial hemorrhage, infection, brain malformation, or general muscular weakness.1 Absence during the newborn period and early infancy is described as highly diagnostic.1
- Asymmetrical — one side different from the other. Usually a local injury rather than a brain problem: damage to a peripheral nerve, a brachial plexus injury, or a fractured clavicle can inhibit the reflex on that side.1
- Exaggerated. Frequently seen in newborns withdrawing from maternal drug use, and in hyperekplexia, a rare genetic condition marked by an excessive startle response and increased muscle tone.1
What persistence does and does not mean
What is documented. Prolonged retention of the Moro reflex can be a sign of spastic cerebral palsy.1 More broadly, persistence of primitive reflexes beyond 4 to 6 months correlates with neurodevelopmental conditions, particularly cerebral palsy and autism.2 And in typically developing preschool children, more strongly retained reflexes have been associated with lower motor efficiency.3
Where that stops. Those are associations found in groups. None of them establishes that a persisting Moro reflex causes a particular difficulty in a particular child, and none of them shows that exercises aimed at the reflex change daily function. Occupational therapy guidance is explicit that a retained reflex does not automatically mean impairment.4
The practical version. A startle response that is still obvious well past six months is a reason to mention it to your child's doctor, alongside anything else you have noticed. It is not by itself a diagnosis, and it is not a reason to buy a program.
If you have been told your child has a retained Moro reflex
The questions worth asking are the same ones that apply to any reflex-integration recommendation, and they are set out in full on the parent article — what functional difficulty is being targeted, how improvement will be measured, and what would make the practitioner change course.
Frequently asked questions
At what age should the Moro reflex be gone?
It begins to fade at around 12 weeks after birth and has usually disappeared completely by 6 months. A second clinical reference gives the window as roughly 4 to 6 months.
Is a missing Moro reflex worse than a persistent one?
In a newborn, yes. Absence during the newborn period and early infancy is described as highly diagnostic and can follow birth injury, asphyxia, hemorrhage, infection, brain malformation or muscular weakness. It warrants prompt medical assessment.
My baby startles on one side more than the other. What does that mean?
An asymmetrical Moro response usually points to a local injury rather than to the brain — a peripheral nerve injury, a brachial plexus injury, or a fractured clavicle can inhibit the reflex on the affected side. It should be examined by a doctor.
Does a retained Moro reflex cause anxiety or attention problems?
That is not established. Persistence of primitive reflexes correlates with some neurodevelopmental conditions in group studies, but correlation in a group does not establish cause in a child, and occupational therapy guidance states that a retained reflex does not automatically mean impairment.
Sources
- Pattnaik P, Al Khalili Y. Moro Reflex. In: StatPearls. StatPearls Publishing; updated August 2, 2025. ncbi.nlm.nih.gov/books/NBK542173 (PMID 31194330). Checked August 25, 2026.
- Chamarthi VS, Gunasekaran V, Daley SF. Primitive Reflexes: Comprehensive Neurological Assessment Across the Lifespan. In: StatPearls. StatPearls Publishing; updated 2026. ncbi.nlm.nih.gov/books/NBK554606 (PMID 32119493). Checked August 25, 2026.
- Gieysztor EZ, Choińska AM, Paprocka-Borowicz M. Persistence of primitive reflexes and associated motor problems in healthy preschool children. Archives of Medical Science. 2018;14(1):167–173. doi:10.5114/aoms.2016.60503 (PMID 29379547).
- American Occupational Therapy Association. Practice guidance on reflex integration programs and occupational outcomes. Checked August 19, 2026.
Medical disclaimer. This page is for general educational purposes and does not constitute medical advice, diagnosis, or treatment. Sensory and motor concerns are best assessed by an occupational or physical therapist who can evaluate your individual child.