the 4-month sleep 'regression'

Understanding the 4-Month Sleep Shift: A Leap Forward in Infant Brain Development

For many parents, the 4-month mark can feel like a sudden curveball in their baby's sleep journey. One week your baby is sleeping in longer stretches, and the next, you're up multiple times a night again. This sudden change is often labeled a "sleep regression" — but what if we reframe it?

According to the work of Dr. Greer Kirshenbaum, a neuroscientist and doula, and Sarah Ockwell-Smith, a gentle parenting expert and author, what's happening at 4 months isn’t a regression at all. It’s actually a progression — a powerful leap forward in your baby’s brain and sleep development.

Let’s explore what’s really going on.

A New Sleep Architecture Is Emerging

At birth, babies’ sleep cycles are relatively simple. They alternate between quiet (deep) sleep and active (REM) sleep, without much structure. But around 3–5 months of age, a fundamental shift begins.

This shift is called the development of adult-like sleep architecture. It means your baby is starting to sleep in stages, just like you do — light sleep, deep sleep, REM — cycling through them every 45 to 60 minutes.

This transition is not a problem. It’s a major milestone in neurological and physiological development. According to Dr. Kirshenbaum, this is evidence of your baby’s brain making new connections, growing more complex, and becoming more integrated.

In other words, your baby isn’t going backward — they’re wiring up for the future.

Why Does Sleep Get Lighter and More Broken?

Here’s where things get tricky for parents. These new sleep cycles mean that your baby will come into lighter stages of sleep more often, and they may wake fully between cycles.

That’s not a flaw in their sleep — it’s how human sleep works. As adults, we do this too, but we usually roll over and drift back off without noticing. Babies, however, are still learning that skill.

Sarah Ockwell-Smith reminds us that waking frequently is biologically normal for babies. It's protective, it supports feeding, bonding, and emotional regulation — all things that are critical to infant survival and development.

The Brain Is Not Regressing — It’s Blooming

Dr. Kirshenbaum encourages us to think of this period as a time of "neurodevelopmental blossoming." The brain is rapidly creating new neural pathways, especially in areas related to:

• Emotional regulation

• Sensory integration

• Memory and learning

• Social connection

Sleep changes reflect this cognitive and neurological leap. Your baby is becoming more aware of the world, more responsive to stimuli, and more in need of connection and comfort to process it all.

This is development, not dysfunction.

What Can You Do To Support Your Baby?

It’s completely natural to feel tired and overwhelmed during this stage. You’re doing a lot. Here are a few gentle strategies to help both you and your baby through this time:

1. Normalize the Wake-Ups

Try not to view waking as a problem to fix. Expecting night waking helps reduce stress. As Sarah Ockwell-Smith says, “When you change the way you view night waking, the waking itself becomes easier to deal with.”

2. Lean Into Connection

Your baby is waking because they’re growing — cognitively, emotionally, and neurologically. Being present to soothe, feed, or hold them during this time is not spoiling them. You’re supporting optimal brain development.

3. Focus on Rhythms, Not Rigid Schedules

Sleep doesn’t need to be controlled; it needs to be supported. Offer consistent nap opportunities, calming bedtime routines, and plenty of time outside in daylight — but don’t stress about precise times or strict routines.

4. Take Care of Yourself Too

You matter in this equation. Ask for help when you need it. Sleep when you can. Let go of perfection. Your baby doesn’t need a perfect parent — just a present one.

A Shift in Perspective

What if we stopped calling this stage a regression, and instead saw it for what it truly is — a remarkable sign of growth?

By understanding the brain science behind the 4-month sleep shift, we can move away from fear-based sleep narratives and toward a more compassionate, informed, and connected approach to parenting.

This phase is hard — but it’s also beautiful. Your baby’s brain is building itself, moment by moment, with every cuddle, every feed, and yes, every wake-up.

You're not going backward — you're both moving forward, together.

Inspired by the work of Dr. Greer Kirshenbaum and Sarah Ockwell-Smith, champions of respectful, neuroscience-informed parenting.