The newborn stage lasts for the first 4 weeks (28 days) of a baby’s life. This period, also called the neonatal period, is defined by rapid physical changes, undeveloped senses, and round-the-clock feeding and sleeping. After 4 weeks, your baby is technically an infant, though the transition feels gradual rather than sudden.
What Happens During Those 4 Weeks
The newborn stage is essentially a period of adjustment. Your baby is transitioning from life inside the womb to life outside it, and nearly every system in their body is calibrating. Newborns lose 7 to 10 percent of their birth weight in the first few days, mostly from shedding extra fluid. Full-term babies typically regain their birth weight within 7 to 10 days. Premature babies can take 10 to 15 days or longer.
Your baby’s umbilical cord stump will dry out and fall off on its own, usually within 1 to 3 weeks after birth. If it hasn’t separated by three weeks, it’s worth mentioning to your pediatrician. Many newborns also develop physiologic jaundice, a yellowish tint to the skin caused by the liver still getting up to speed. This typically appears within 24 hours of birth, peaks around 2 to 4 days, and resolves by 2 to 3 weeks without treatment in most cases.
Sleep in the Newborn Stage
Newborns sleep a lot, roughly 16 to 17 hours per day, but in frustratingly short stretches. Most sleep only 1 to 2 hours at a time before waking to feed. There’s no real pattern to it: newborns don’t develop regular sleep cycles until around 6 months of age. During the newborn stage, day and night are essentially meaningless to your baby, which is why it can feel so disorienting for parents.
Feeding and Stomach Size
At birth, your baby’s stomach is about the size of a toy marble, holding just 1 to 2 teaspoons of milk. This is why newborns need to eat so frequently, often every 1 to 3 hours. By around day 10, the stomach grows to roughly the size of a ping-pong ball, holding about 2 ounces. That growth explains why feedings gradually space out slightly toward the end of the newborn stage, though they’re still frequent.
How Newborns See and Respond
A newborn’s vision is blurry. They can focus best on objects about 8 to 12 inches from their face, which happens to be roughly the distance between your face and theirs during feeding. They can’t see color well and prefer high-contrast patterns. Their world is small and close.
Newborns come equipped with a set of automatic reflexes that serve as early survival tools. The rooting reflex makes them turn their mouth toward anything that touches their cheek, helping them find the breast or bottle. The Moro reflex, sometimes called the startle reflex, causes them to throw their arms out and cry when they feel a sudden loss of support. The grasping reflex makes them curl their fingers tightly around anything pressed into their palm. These reflexes are all present at birth. Rooting begins to fade after the first month, while the Moro and grasping reflexes stick around until about 6 months.
How the Transition to Infancy Looks
The shift from “newborn” to “infant” at 4 weeks is a medical definition, not a dramatic overnight change. But real developmental shifts do start appearing right around that boundary. By about 2 months, most babies can support their head when held upright, begin smiling in response to faces, and start making cooing and vowel sounds. By 3 months, many can lift their head and chest while lying on their stomach, and some start experimenting with squeals, growling sounds, or blowing raspberries.
These milestones, social smiling, early head control, and purposeful sounds, mark the point where your baby starts engaging with the world rather than simply reacting to it. The newborn stage is defined by reflexes and basic survival. What comes next is interaction. That’s the clearest line between the two, and most parents notice it without anyone having to tell them.