Premature babies sleep more than infants born at full term, spending up to 90% of their day asleep compared to about 75% for a newborn. This extensive sleep is a requirement for their development. Because they are born before 37 weeks of gestation, premature infants must complete a significant portion of their physical and cognitive maturation outside the womb. Sleep facilitates the accelerated growth and development needed to catch up.
The Developmental Need for More Sleep
A premature baby’s brain undergoes rapid development, and sleep is the primary state for this work. Much of the brain’s architecture, including the formation of neural connections, is built during slumber. This dedicated time allows the brain to mature and organize without the demands of wakefulness.
Sleep also serves as a method for energy conservation. Premature infants have minimal fat reserves and must dedicate their caloric intake to survival. By minimizing activity, sleep frees up energy for functions like breathing, maintaining body temperature, and fueling physical growth.
Extended sleep also helps replicate the low-stimulation environment of the uterus. The womb provides a dark, quiet space for development with minimal interruption. By sleeping for long periods, premature babies simulate this protected state, allowing their bodies and brains to continue maturing.
Characteristics of Preemie Sleep
A premature baby’s sleep is not just longer; it is structurally different from that of a full-term infant. Preemies experience shorter sleep-wake cycles, often waking every hour for care and feeding. Their sleep is also lighter and more active, and these frequent arousals are a normal part of their adjustment to the outside world.
Preterm infants spend a greater proportion of their sleep in “active sleep,” which is similar to REM sleep in adults. The other primary state is “quiet sleep,” a deeper, non-REM phase. Active sleep is characterized by twitching limbs, facial movements, and irregular breathing patterns, and is associated with high levels of brain activity.
The visible signs of active sleep can be misinterpreted as restlessness or distress. However, the twitches, fluttering eyelids, and uneven breathing are normal physiological behaviors. These actions indicate the brain is busy maturing, which can be reassuring for parents.
Sleep Progression After the NICU
As a premature baby grows, their sleep patterns begin to mature and resemble those of a full-term infant. This progression is tracked using the baby’s “adjusted age,” which is calculated from their original due date rather than their birth date. For example, a baby born eight weeks early is considered to have an adjusted age of two months when they are four months old. Sleep milestones are more likely to align with this adjusted timeline.
The transition from the NICU to home marks a significant change in the baby’s sensory environment. The quieter, darker setting of a home replaces the constant light and noise of the NICU, which helps establish a day-night cycle. At home, caregivers can introduce calming bedtime routines and keep nighttime interactions quiet and with low lighting to reinforce this cycle.
Upon bringing a preemie home, it is important to implement safe sleep practices. Babies born prematurely have a higher risk of Sudden Infant Death Syndrome (SIDS). This includes always placing the baby on their back to sleep, using a firm sleep surface, and keeping the crib free of soft bedding, bumpers, and toys.