Bakit Nagugulat si Baby? A Doctor Explains the Moro Reflex in Newborns

Your newborn is sleeping peacefully—then suddenly flings their arms out, arches their back, and cries. Before you panic, know this: what you just witnessed is the Moro reflex, and it means your baby's nervous system is working exactly as it should.

Here, board-certified pediatrician Dr. Sandra Sharlene Lim Uy—who has spent the last five to six years caring for newborns and premature infants in the NICU at Taguig Pateros District Hospital—breaks down what triggers this newborn reflex, how to soothe your baby through it, and when to call your doctor.

What Is the Moro Reflex?

You might wonder what causes your baby to jolt awake so suddenly. The Moro reflex is one of the core baby reflexes present at birth—and it tells pediatricians a lot about your baby's early neurological development.

It's your baby's first protective instinct.

Dr. Lim Uy describes it plainly: “The Moro reflex is a primitive survival reflex in babies. It helps them catch the attention of their caregiver—or even embrace them [sic]—when startled or when they lose their balance.”

Think of it as your newborn’s built-in distress signal, an automatic way of asking to be held and protected. It’s also something pediatricians actively check for during a newborn’s neurological examination.

It causes a sudden, full-body startle reaction.

When the reflex is triggered, your baby’s body reacts in a very specific pattern. Dr. Lim Uy notes that the arms abduct, meaning they extend away from the body. Their fingers also spread outward. You’ll notice a slight extension of the neck and the spine. After this initial outward movement, your baby will quickly pull their arms back in toward their chest.

It fades as your baby's nervous system matures.

If you’re wondering, when does the Moro Reflex go away? The timeline varies from baby to baby. The American Academy of Pediatrics (AAP) notes it typically peaks in the first month and starts fading around two months.

Dr. Lim Uy adds that it's usually completely gone by six months. As your baby gains better head and muscle control, their neurological development progresses, and the newborn startle reflex phase naturally ends. Until that happens, it helps to know the most common everyday experiences that trigger the reflex.

Common Triggers That Startle Your Newborn

Your newborn is still learning how to process the sights, sounds, and sensations around them. In the first few months, their sensory system responds intensely to abrupt changes in their environment, which is why this startle response seems to go off so easily. The more you recognize what sets it off, the better you can anticipate and reduce unnecessary startles.

Startling loud sounds in the room can activate the reflex.

According to Stanford Medicine Children's Health, the Moro reflex most commonly occurs when a baby is startled by a loud sound or movement. Even a baby's own cry can startle them and trigger the reflex all over again. Keep their surroundings quiet by moving them away from household noises like slamming doors, blaring TVs, or barking dogs.

A sudden feeling of falling triggers the response.

Placing your baby down face-up creates a falling sensation that triggers the Moro reflex even when they’re sound asleep.

This is the most common trigger you’ll encounter. It often happens when you lower your sleeping baby into a crib. If the movement is too sudden, your baby may sense a loss of support. That sensation immediately triggers the reflex, sending their arms out as if to catch themselves. This is why even careful, well-meaning movements can catch your baby off guard.

Simple Ways to Soothe Your Startled Baby

When a quick movement, loud sound, or falling sensation jolts your baby awake, it interrupts their sleep and causes them to cry. While it can be frustrating during naps or nighttime sleep, there are a few simple steps you can take to help them calm down quickly.

Dr. Lim Uy recommends picking your baby up and cuddling them immediately—or letting them lie flat against your chest. This close physical contact gives them the reassurance they’re instinctively asking for.

If your baby startles while sleeping, swaddling can also help them feel more secure. The AAP recommends always placing a swaddled baby on their back, keeping the wrap loose enough for their hips to move freely, and stopping once your baby starts showing signs of rolling—usually around 3 to 4 months. For more ways to support restful sleep, read this guide to healthy baby sleep habits.

When to Consult Your Pediatrician

The Moro reflex is an expected part of infant development. However, there are times when the way your baby startles is worth a conversation with your doctor. Your pediatrician tracks these movements to make sure your baby's motor development stays on the right path.

The reflex happens only on one side.

The newborn startle reflex should look the same on both sides of the body. “It is a symmetric reflex,” Dr. Lim Uy explains. “If it is asymmetric, it could be an indication of damage from a difficult delivery.” If you notice a one-sided reaction, bring it up with your pediatrician for evaluation.

The reflex is exaggerated or happens with very little stimulation.

Another cause for concern is if the response seems unusually intense or fires constantly with minimal trigger. Dr. Lim Uy notes that “an exaggerated Moro reflex may indicate a rare condition called hyperekplexia.” Your doctor can evaluate whether the reaction falls within the expected range or warrants further assessment.

The reflex stays past six months of age.

This reflex follows a fairly predictable timeline in healthy infants. “It begins to disappear by 12 weeks and is completely gone by 6 months,” says Dr. Lim Uy. “Past five months, they may need to go back to their pediatrician”—and possibly be referred to a pediatric neurologist or developmental pediatrician for further evaluation.

Your Newborn Is Right on Track

Swaddling creates a cozy boundary that keeps your baby's arms close to their body, helping prevent sudden reflex awakenings.

The Moro reflex can catch any new parent off guard—but now you know what it is, what sets it off, and how to respond. This newborn reflex is a typical part of healthy early development. It peaks in the first month, starts fading around two to three months, and disappears completely by six months. In the meantime, picking your baby up, holding them close, and swaddling them safely are all you need to help them feel secure.

If the reflex looks asymmetric, seems unusually intense, or lingers past six months, trust your instincts and check in with your pediatrician.

Every baby hits these milestones a little differently—and sometimes it helps just to hear that another parent has been through the same 3 a.m. newborn startle reflex. Join the ParenTeam Moms and Dads Facebook group and swap stories or ask questions about your baby’s Moro reflex.

About Dr. Sandra Sharlene Lim Uy
Dr. Sandra Sharlene Lim Uy is a board-certified pediatrician with a deep commitment to newborn and premature infant care. For the past five to six years, she has served as a dedicated pediatrician in the Neonatal Intensive Care Unit (NICU) at Taguig Pateros District Hospital, guiding countless families through the critical early days of their premature babies' lives.