The Moro Reflex: What Is It and When Should It Disappear?
Written by
The Village Team
Published
Clinically reviewed by
Mary Gianatasio, MA in Child Psychology
Founding Clinical Member
Many parents notice it in the early weeks of life: their baby suddenly throws their arms outward, opens their hands wide, and appears startled - often followed by crying or quickly curling back inward. This automatic reaction is called the Moro reflex, also known as the startle reflex, and it is a completely normal part of early infant development.
Although it can sometimes surprise parents, the Moro reflex is a normal part of early infant development and one of several primitive reflexes healthcare providers monitor as the nervous system matures.
What Is the Moro Reflex?
The Moro reflex is an automatic reflex present at birth. It occurs when a baby experiences a sudden change in position or perceives an unexpected sensory stimulus such as:
A sudden movement
A loud sound
A bright light
A sensation of falling backward
When triggered, babies typically:
Extend their arms outward
Open their fingers
Extend the neck and body
Quickly pull the arms back inward
Often cry or appear startled
This reflex was first described by pediatrician Ernst Moro in 1918 and is considered an important marker of early neurological development.
When Does the Moro Reflex Develop?
The Moro reflex begins developing in utero between approximately 28–32 weeks of gestation and is typically present at birth in healthy infants.
The reflex usually begins to fade between 2 and 4 months of age and is typically integrated by about 6 months as babies gain better head control and nervous system maturity.
As higher brain centers develop, infants gradually transition from reflexive movements toward more voluntary and coordinated motor control.
Why Is the Moro Reflex Important?
Primitive reflexes are designed to support survival and early development during infancy. The Moro reflex is believed to help infants respond to sudden environmental changes and may play a role in early protective responses and nervous system activation.
Some researchers have also proposed that the Moro reflex may serve as an early form of nonverbal communication, signaling a need for comfort, physical closeness, or regulation from a caregiver.
Beyond its survival role, the reflex also provides insight into the development of the brain and nervous system. Pediatricians routinely assess the Moro reflex during newborn and infant examinations to help evaluate neurological function and developmental progression.
How Doctors Test the Moro Reflex
During routine pediatric visits, healthcare providers may perform a Moro reflex assessment.
Typically, the baby is gently supported while the position of the head is briefly and carefully shifted backward in a safe, controlled manner. This creates a sensation of falling, which naturally triggers the reflex response.
A typical Moro response includes:
Symmetrical arm extension
Finger spreading
Arm flexion back toward the body
A brief startle reaction
The presence, symmetry, strength and timing of the reflex can provide valuable information about nervous system development.
Other Common Primitive Reflexes in Babies
The Moro reflex is just one of several primitive reflexes present during infancy. Other important newborn reflexes include:
Rooting Reflex
When a baby’s cheek or mouth is touched, they turn toward the stimulus and open their mouth to help locate the breast or bottle for feeding.
Sucking Reflex
Touching the roof of the mouth stimulates sucking movements that support feeding.
Grasp Reflex
Babies naturally curl their fingers around an object placed in the palm of the hand or curl their toes when the soles of the feet are touched.
Stepping Reflex
When held upright with the feet touching a surface, infants may appear to take stepping movements.
Tonic Neck Reflex
Sometimes called the “fencing reflex,” this occurs when babies turn their head to one side and extend the arm on that side while bending the opposite arm.
Together, these reflexes help support feeding, movement, sensory development, and early neurological organization.
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What if the Moro Reflex Persists?
As babies mature, primitive reflexes are expected to integrate naturally. When a reflex remains active beyond the typical developmental window, it is sometimes referred to as a retained primitive reflex.
Some clinicians and developmental specialists observe that a retained Moro reflex may be associated with increased sensitivity to sensory input or stress responses in certain children.
Clinicians and developmental specialists sometimes observe associations with:
Heightened startle responses
Sensory sensitivities
Emotional reactivity
Difficulty with self-regulation
Challenges with attention or transitions
However, reflex retention itself is not considered a diagnosis. Rather, it may reflect ongoing patterns within nervous system development and regulation.
Premature infants may also retain primitive reflexes longer than full-term infants because neurological and muscular development continues according to adjusted developmental age.
It is also important to remember that sensory sensitivities, emotional reactivity, and attention challenges can have many contributing factors and are not caused by primitive reflexes alone.
An Integrative Perspective on Nervous System Development
From an integrative perspective, infant development involves the dynamic interaction of movement, sensory input, attachment, nutrition, sleep, and environmental experiences.
Primitive reflexes are one part of this broader developmental process. Healthy nervous system maturation is supported through:
Responsive caregiving and co-regulation
Adequate sleep and restorative rhythms
Skin-to-skin contact and bonding
Nutrient-rich nutrition for infant and maternal health
Sensory-rich movement and play
Calm, supportive environments that reduce excessive stress
These early experiences help support the development of stress regulation, emotional regulation, sensory processing, and healthy nervous system organization during infancy and early childhood.
When Should Parents Seek Guidance?
The Moro reflex is a normal and expected part of infancy. However, parents may wish to speak with a pediatrician or developmental specialist if they notice:
Significant asymmetry in the reflex
Absence of the reflex in infancy
Extreme or persistent startle responses
Ongoing reflex patterns beyond the expected age range
Concerns about motor, sensory, or developmental milestones
An evaluation can help determine whether additional developmental support or monitoring may be beneficial.
Final Thoughts
The Moro reflex is one of the earliest reflexes seen in infancy and an important part of early nervous system development. Although it may appear dramatic, this reflex reflects the brain and body learning to respond to the surrounding world.
As babies grow, the Moro reflex gradually fades as more mature movement patterns and nervous system regulation develop. Through responsive caregiving, sensory experiences, movement, nutrition, sleep, and emotional connection, parents help support the neurological foundations that guide development throughout childhood.
References
Pattnaik P, Al Khalili Y. Moro Reflex. [Updated 2025 Aug 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK542173/
