Your newborn won’t sleep for one simple reason: newborns aren’t biologically equipped to sleep the way adults expect them to. Their brains don’t produce melatonin (the hormone that drives a day-night cycle) until around 3 to 5 months of age, which means they have no internal signal telling them it’s nighttime and they should sleep for long stretches. But beyond that basic biology, several fixable problems can make an already difficult situation worse.
Newborns Don’t Have a Body Clock Yet
Adults fall asleep at night partly because their brains release melatonin when it gets dark. Newborns can’t do this. The pineal gland is present at birth, but it isn’t capable of producing melatonin until 4 to 6 months of age. A stable circadian rhythm, where a baby reliably sleeps longer at night than during the day, typically doesn’t emerge until somewhere between 3 and 6 months.
Research tracking infant movement patterns found that a consistent nighttime sleep period only became detectable in groups of babies around 13 to 15 weeks of age. Before that, sleep is scattered across the entire 24-hour day in short bursts. So if your newborn seems to have no concept of day versus night, that’s not a problem you’re creating. It’s the expected state of their developing brain.
About half of a newborn’s roughly 16 hours of daily sleep is spent in REM (active) sleep. During REM, babies twitch, make faces, breathe irregularly, and wake easily. This means even when your baby does fall asleep, the sleep is light and fragile for much of it. They cycle through sleep stages quickly and surface to wakefulness between cycles far more often than adults do.
They Might Be Overtired
This sounds counterintuitive, but a baby who has been awake too long actually has a harder time falling asleep. When a newborn stays awake past the point of tiredness, their body releases stress hormones, including cortisol and adrenaline. These flood a tiny system that can’t regulate them well, creating a baby who seems wired, fussy, and impossible to calm down. You may notice them looking almost hyperactive, with jerky movements and inconsolable crying, despite being exhausted.
The fix is catching the sleep window before it closes. Newborns from birth to one month can only handle about 30 to 60 minutes of awake time before they need to sleep again. From 1 to 3 months, that window stretches to roughly 1 to 2 hours. If you’re waiting for obvious sleepiness cues like yawning, you may already be past the window. Timing awake periods by the clock, not just by behavior, helps prevent the overtired spiral.
Hunger Is the Most Common Reason
A newborn’s stomach is remarkably small. On day one, it’s about the size of a marble and holds only 1 to 1.5 teaspoons of milk per feeding. By day three, it’s roughly the size of a ping pong ball, holding about 4.5 to 5.5 teaspoons. By day ten, it’s closer to the size of a large egg, holding 2 to 2.75 ounces. It doesn’t reach about 4 ounces per feeding until 3 or 4 months.
Because their stomachs empty quickly, newborns need to eat 8 to 12 times per day, roughly every 2 to 3 hours. A baby who seems unable to settle may simply need to eat again, even if the last feeding feels like it just ended. Growth spurts make this more intense. They commonly hit around 2 to 3 weeks, 6 weeks, 3 months, and 6 months, though every baby varies. During a growth spurt, your baby may cluster feed, wanting to eat every 30 to 60 minutes for several hours, and refuse to sleep between sessions. This is temporary and typically resolves within a few days.
The Startle Reflex Keeps Waking Them
Newborns are born with the Moro reflex, an involuntary startle response that causes them to suddenly fling their arms outward and then pull them back in. It can be triggered by a loud sound, a sudden movement, the sensation of falling, being set down too quickly, or even by their own arm twitching during sleep. This reflex is strong enough to jolt a sleeping newborn fully awake, sometimes within minutes of finally drifting off.
The Moro reflex is present at birth, peaks in the first month, begins to fade around 2 months, and usually disappears by 4 to 6 months as the brain matures and the baby gains more voluntary control over their movements. In the meantime, swaddling (wrapping the baby snugly with arms contained) is the most effective way to prevent the reflex from disrupting sleep. Once a baby shows signs of rolling over, swaddling the arms is no longer safe.
Physical Discomfort You Might Not See
Some newborns who resist sleep are dealing with physical discomfort that isn’t always obvious. Reflux is one of the most common culprits. In typical reflux, you’ll see spit-up. But in silent reflux, stomach acid rises into the esophagus without visible vomiting, causing pain that worsens when a baby lies flat. Signs include arching of the back during or after feeding, gagging, irritability that peaks after meals, refusing to eat, and wheezing or coughing. If your baby seems to fight being placed on their back specifically, reflux is worth considering. Holding your baby upright for 30 minutes after feedings can reduce symptoms.
Another overlooked cause is infant dyschezia, which is not constipation but rather a newborn’s struggle to coordinate the muscles needed to pass a bowel movement. Babies with dyschezia may strain, grunt, scream, turn red, and kick for 10 minutes or more while trying to poop. The key difference from constipation is that when the poop finally comes out, it looks soft and normal. This is a coordination problem, not a stool problem, and it resolves on its own as the baby’s nervous system matures. But in the meantime, those straining episodes can absolutely prevent sleep or cut it short.
Their Environment May Be Off
Newborns are sensitive to temperature, light, and noise in ways that can be easy to misjudge. Overheating is a particularly common sleep disruptor. Parents tend to bundle newborns in too many layers, and a baby who is too warm will be restless and fussy without an obvious cause. A good check is feeling the back of their neck or their chest. If the skin is hot or sweaty, they’re overdressed. Keep the room at a temperature comfortable for a lightly clothed adult.
Light exposure matters too, even before the circadian rhythm is established. Bright light suppresses the early building blocks of melatonin production, so keeping the environment dim during nighttime feedings and diaper changes helps reinforce the day-night pattern your baby is slowly developing. During the day, exposing your baby to natural light can help nudge that internal clock along, even if the effects won’t be visible for weeks.
What “Normal” Actually Looks Like
If your newborn sleeps in stretches of 45 minutes to 2 hours, wakes frequently to feed, and takes 10 to 20 minutes of soothing to fall asleep, that is normal. It doesn’t feel normal at 3 a.m., but it’s exactly what a healthy newborn brain is designed to do. The absence of melatonin, the tiny stomach, the active sleep cycles, and the startle reflex all work together to create a baby who sleeps in short, unpredictable bursts for the first several months.
Most of the factors keeping your newborn awake are developmental and will resolve on their own between 3 and 6 months as the brain matures, melatonin production begins, the stomach grows, and the Moro reflex fades. In the short term, the most impactful things you can do are respect the very short wake windows, swaddle to contain the startle reflex, feed frequently enough to stay ahead of hunger, and keep the baby upright after feedings if reflux seems to be a factor.