Understanding Your Baby’s Sleep Cycles By Sweet Slumber – Your Partner in Restful Nights
What Is a Sleep Cycle?
While the wake–sleep cycle is guided by our circadian rhythm (day and night patterns), the sleep cycle describes what happens during those sleep periods.
For newborns, sleep is split almost evenly between Active Sleep (REM) and Quiet Sleep (NREM), and interestingly, newborns begin sleep in the REM stage.
When Sleep Cycles Mature
Around 3–4 months, your baby’s sleep starts to take on a more structured pattern similar to adults. This developmental milestone is one of the main reasons behind the well-known 4-month sleep regression (which we’ll explore in a future lesson).
By about 6 months, your baby’s sleep cycles begin to resemble an adult’s, shifting from starting in REM to beginning with NREM sleep. At this stage, babies experience the different phases of NREM sleep, each with a unique purpose.
The Stages of NREM Sleep
Stage 1: The drowsy, drifting-off stage, the transition from wakefulness to sleep.
Stage 2: A slightly deeper sleep where the brain produces sleep spindles and K-complexes, vital for memory and brain development. K-complexes also help block out external sounds that might otherwise wake your baby.
Stage 3: Also known as Slow Wave Sleep (SWS) the deepest, most restorative stage that supports physical recovery and growth.
At the end of each sleep cycle, babies experience a brief arousal. Ideally, they settle back into NREM sleep and begin a new cycle. However, if they fully wake and struggle to resettle, sleep challenges can begin to emerge.
It’s normal for younger babies to wake frequently for feeds or comfort, but as sleep consolidates around 5–6 months, frequent wakings may signal a need for support and that’s often when parents seek help from a sleep consultant.
How Long Is a Baby’s Sleep Cycle?
Research varies when it comes to the exact length of an infant’s sleep cycle. In Dr. Richard Ferber’s book “Solve Your Child’s Sleep Problems” (1985, revised 2006), he describes longer stretches of deep sleep early in the night (up to 2 hours) followed by shorter cycles later on. However, he doesn’t cite specific clinical evidence to support these timings.
In my experience at Sweet Slumber, I’ve observed a wide range of sleep cycle lengths from as short as 28 minutes to as long as 60 minutes, with 40–45 minutes being the most common. These findings align with older studies on infant sleep patterns.
While longer stretches of deep sleep (3–5 hours) are common earlier in the night, these likely represent extended periods of slow wave sleep, which naturally reduce as the night progresses. There’s still much to learn and more research is definitely needed but the shorter, cyclical nature of infant sleep seems clear.
Why Environment and Sleep Support Matter
You may notice that your baby’s naps are shorter when they sleep on the move in the pram, car seat, or sling. That’s because light, noise, and movement can prompt brief awakenings at the end of a cycle.
Similarly, when a baby falls asleep while being rocked, fed, or held, part of their sleep cycle occurs during that support. Once they’re placed down, the remaining portion of the cycle can seem shorter, as their brain recognises the change in environment.
The “Drowsy But Awake” Myth
You’ve probably heard the advice to put your baby down “drowsy but awake.” But here’s something to consider: “drowsy” is actually the first stage of sleep. By that point, your baby’s brain has already begun falling asleep often associating sleep with the action that got them there (rocking, feeding, bouncing, etc.).
When they’re transferred to their sleep space, they may wake suddenly and become upset, making it harder to settle the second time. While some babies can learn to self-settle from this state, it often requires great care and consistency something we’ll dive into more deeply in a future lesson.
How Sleep Cycles Evolve With Age
A fascinating research paper shows that between ages 2 and 5 years, children’s number of sleep cycles per night decreases, with most 5-year-olds experiencing around six cycles total. This reflects a natural lengthening of sleep cycles as children grow.
Final Thoughts from Sweet Slumber
Understanding how sleep cycles work can be a game-changer for parents. It explains why babies sometimes wake “like clockwork,” why naps can be short in certain environments, and why those first months bring so many changes.
At Sweet Slumber, we believe that by understanding the why behind your little one’s sleep, you’re already taking the first step toward calmer nights and more confident days.
Sweet dreams,
The Sweet Slumber Team
