Baby's First Year
Month 4 — The Great Sleep Regression
Baby This Month
approximately 62–66cm and 6–7kg
Month 4 is big developmentally — and if sleep suddenly goes haywire, that's why. Your baby's sleep cycles are maturing from simple newborn patterns into more complex adult-like cycles that include light sleep phases. This means they wake more between cycles and need to learn to link them. On the upside: your baby is increasingly social and interactive, laughing out loud, reaching for and grasping toys deliberately, and bringing everything to their mouth to explore. Tummy time is getting stronger — many babies can push up onto extended arms now, like a mini push-up.
The 4-month check with your paediatrician or health visitor covers growth, development, and vaccinations — a third round typically happens now. Your baby still needs breast milk or formula exclusively — no solids yet. The World Health Organisation recommends starting solids at around 6 months; starting too early increases the risk of allergies and digestive issues. If anyone is pressuring you to start rice cereal at 4 months, you can politely ignore them.
The 4-month sleep regression is the only regression that isn't actually a regression at all — your baby's sleep is permanently changing into a more mature pattern. The shift is permanent, but that doesn't mean broken sleep is permanent. Most babies who were poor sleepers before this stage find sleep easier to navigate as their brains mature, especially with consistent routines.
Introduce a consistent bedtime routine this month if you haven't yet — bath, feed, dim lights, song, sleep. The specific activities matter less than the consistency and sequence. By doing the same things in the same order every night, your baby's brain learns to anticipate sleep and starts producing melatonin earlier in the sequence. Within a few weeks, you'll notice your baby getting drowsy just at the sight of the bath.
Continue exclusive breastfeeding or formula feeding — no solids yet regardless of hunger cues, as the gut needs more time to develop the right enzymes and barrier function.
This content is for informational purposes only and is not medical advice. Read full disclaimer
The 4-month sleep regression is hard on everyone — be patient, take shifts, and remember it's temporary. This is often when parental fatigue peaks and tempers can fray.
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