The Moro reflex is elicited by gently pulling up on a newborn’s arms and then suddenly letting go. This brief sensation of falling triggers a two-phase startle response that clinicians use to assess neurological health in the first months of life. The technique is simple, but the details matter for getting a reliable response and knowing what to look for.
The Standard Elicitation Technique
The most common method involves the infant lying face-up on a flat surface. You gently grasp both of the baby’s hands or wrists and lift the arms upward, just enough to shift the baby’s weight slightly. Then you release both hands simultaneously. The key point, as Stanford Medicine emphasizes, is that the reflex is produced by the suddenness of the stimulus, not the distance of the fall. There is no need to lift the infant off the surface, though the shoulders may rise slightly.
A related approach uses head position rather than the arms. While supporting the baby’s head with one hand, you allow the head to drop back slightly, just a few centimeters, before catching it again. The momentary sensation of falling backward is enough to trigger the reflex. In both methods, the movement should be quick but controlled. You’re creating a brief moment of surprise, not a jarring drop.
Other Ways to Trigger the Reflex
Physical manipulation isn’t the only option. A sudden loud noise, like a clap or a firm tap on the surface near the baby, can also produce the Moro reflex. Some practitioners snap their fingers near the infant’s ears while the baby’s eyes are closed. Any abrupt sensory change that startles the baby, whether it’s sound, a sudden movement of the surface they’re lying on, or the sensation of falling, can work as a trigger.
That said, the arm-pull or head-drop method is preferred in clinical settings because it’s more standardized. Noise-based triggers depend on how loud the sound is, the ambient noise level, and how alert the baby happens to be at that moment. The physical method produces more consistent results.
What a Normal Response Looks Like
A complete Moro reflex has two distinct phases. In the first phase, the baby’s arms and legs extend outward. The arms reach out to the sides with palms facing up and thumbs flexed outward. The baby’s fingers spread apart, and their face takes on a startled expression. This whole extension happens almost instantly.
In the second phase, the baby draws everything back in. The arms return to the body, the elbows flex, and the hands close. The baby relaxes. This retraction phase typically starts as soon as you support the baby’s head again or the sensation of instability passes. Both phases together take only a couple of seconds. The response should be symmetrical, meaning both arms and both legs move equally.
When the Reflex Is Present and When It Fades
The Moro reflex develops before birth. Fetuses can show it as early as the second trimester, though it more reliably appears during the third trimester. It’s strongest in the first few weeks after birth and is a standard part of the newborn neurological exam.
By around 6 months of age, the Moro reflex should be gone. It gradually converts to a mature startle response (sometimes called the Strauss reflex), which is subtler and doesn’t involve the dramatic arm extension. This transition is a normal sign that the brain’s higher cortical areas are taking over from the primitive brainstem reflexes that dominate early life.
What an Abnormal Response Means
Clinicians pay close attention to three types of abnormal findings: an asymmetric response, a completely absent reflex, or a reflex that persists well past 6 months.
An asymmetric Moro reflex, where one arm extends normally but the other doesn’t, can point to a problem on the weaker side. A fractured collarbone is one of the most common causes, particularly after a difficult delivery. Injury to the nerves that run from the neck into the arm (a brachial plexus injury) can also produce a one-sided response. In these cases, the baby may extend and retract one arm normally while the other barely moves.
A completely absent Moro reflex on both sides is more concerning. According to UF Health, bilateral absence suggests damage to the brain or spinal cord. This could result from birth trauma, oxygen deprivation, infection, or a congenital neurological condition. An absent reflex will prompt further evaluation, often including imaging or specialist consultation.
Persistence of the reflex beyond 6 months, or its reappearance later in life, can also signal central nervous system problems. In older infants, a retained Moro reflex may indicate that the brain isn’t maturing along the expected developmental timeline.
Getting a Reliable Result
A few practical factors affect how cleanly you can elicit the reflex. The baby should be awake but calm. A deeply sleeping infant may have a muted response, and a baby who is already crying or agitated may be difficult to read because their limbs are already moving. Laying the baby on a firm, flat surface gives you a consistent baseline.
If the first attempt doesn’t produce a clear response, wait a minute or two before trying again. Repeated stimulation in quick succession can temporarily dampen the reflex, making it look weaker than it actually is. One or two well-timed attempts are better than several rapid ones.
When performing the arm-pull method, keep the motion gentle. You’re lifting just enough to create slight instability when you release. The baby’s back should stay on or very near the surface throughout. For the head-drop approach, the drop distance should be minimal, only a few centimeters, and your hand should always be ready to catch the head immediately.