What Every Parent Should Know

Ever wonder *why* your baby sleeps in short bursts, fights naps, or wakes up just when you finally sit down? It’s not just a mystery there’s real science behind it. Understanding how your baby’s brain and body develop can give you clarity, confidence, and compassion as you navigate sleep.

1. The Basics: How Baby Sleep Works

Babies aren't born with mature sleep cycles. In fact, newborns cycle between light (REM) and deep sleep much faster than adults, about every 45–60 minutes. They also spend more time in light sleep, which is why they’re so easily startled awake.

At around 4 months, a baby’s sleep begins to mature. This is when the “4-month sleep regression” can hit because their brain is literally changing how it sleeps. I like to reframe this in a positive way and call this a sleep progression.

2. Circadian Rhythms: The 24-Hour Body Clock

Babies don’t start developing a circadian rhythm (a natural day-night cycle) until around 6–8 weeks of age, and it doesn’t fully mature until closer to 3–6 months. This is influenced by exposure to natural light, consistent routines, and feeding schedules. Helping your baby distinguish day from night is key in the early weeks.

3. Sleep Pressure: The Science of Feeling Tired

“Sleep pressure” builds in the brain the longer we stay awake. Think of it like a balloon filling up. When the pressure is high, sleep comes easily. But if you miss that optimal window, the balloon can “pop,” leading to a wired, overtired baby.

Recognising and responding to sleep cues (like rubbing eyes, zoning out, or hyperactive) can help your baby fall asleep faster and stay asleep longer.

4. Hormones: The Role of Melatonin and Cortisol

Melatonin, the sleepy hormone, is triggered by darkness and starts to rise in babies around 8–12 weeks.
Cortisol, the alert hormone, spikes when babies are overtired or overstimulated.

A consistent bedtime routine and dim lighting in the evenings help support melatonin production and make bedtime smoother.

5. Why This Matters for Parents

When you understand the why behind your baby’s sleep patterns, it becomes easier to:

Set realistic expectations
Build a routine that supports natural rhythms
Feel less guilt or frustration when things go off track

You’re not “failing”, your baby is learning. And their little brain is doing exactly what it’s supposed to do.

Takeaway Tips:

Focus on light during the day and dark in the evenings to support circadian rhythms
Keep awake windows age-appropriate to manage sleep pressure
Create calming wind-down routines to support hormone balance
Be patient during regressions/progressions, they’re signs of healthy development

Want support making sense of your baby’s sleep and creating a plan that works with their natural rhythms? Let’s chat, I’d love to help you feel confident and calm.

I’ve got you,

Clare

You baby sleep and travel concierge

Trusted Sources & References:

Sleep Cycles and Infant Sleep Development
- American Academy of Pediatrics
- Galland, B., et al. (2012). Normal sleep patterns in infants and children: a systematic review of observational studies. Sleep Medicine Reviews.
Circadian Rhythms
- Figueiro, M.G., et al. (2004). The impact of light on circadian rhythms in infants and young children. Sleep Health Journal.
Sleep Pressure & Wake Windows
- Mindell, J.A., & Owens, J.A. (2015). A Clinical Guide to Pediatric Sleep: Diagnosis and Management of Sleep Problems.
- Wong, S.D., Wright Jr, K.P., Spencer, R.L., Vetter, C., Hicks, L.M., Jenni, O.G. and LeBourgeois, M.K., 2022. Development of the circadian system in early life: maternal and environmental factors. Journal of physiological anthropology, 41(1), p.22.
- LeBourgeois, M.K., Wright Jr, K.P., LeBourgeois, H.B. and Jenni, O.G., 2013. Dissonance between parent‐selected bedtimes and young children's circadian physiology influences nighttime settling difficulties. Mind, Brain, and Education, 7(4), pp.234-242.
Melatonin & Cortisol in Infants
- Kennaway, D.J. (2015). Melatonin research in pediatric sleep disorders: Recent advances and future perspectives. Journal of Pineal Research.
- Bathory, E., & Tomopoulos, S. (2017). Sleep regulation and hormones in early infancy. Pediatrics in Review.

The science of Baby Sleep: