4-Month Sleep Regression: What's Happening to Our Baby?

Just when we thought we had figured out sleep, everything fell apart. Our baby who was sleeping 5-hour stretches suddenly woke up every 2 hours. Welcome to the 4-month sleep regression - the phase no one warns you about.

What is Sleep Regression?

Here's the surprising truth: it's not actually a "regression." It's a progression in your baby's brain development.

Around 4 months, your baby's sleep architecture matures. They transition from newborn sleep (only 2 stages) to adult-like sleep (4-5 stages including light sleep). This is permanent and good!

But this maturation means:

• More time in light sleep = more opportunities to wake up
• Sleep cycles become shorter (about 45 minutes)
• Baby wakes between cycles and can't get back to sleep alone

Symptoms We Experienced

Waking Every 2 Hours

Our baby went from 4-5 hour stretches to waking every 90 minutes to 2 hours. It felt like having a newborn again - except we were more exhausted because we'd gotten used to longer sleep.

40-Minute Naps

Naps became frustratingly short. She'd sleep exactly one sleep cycle (40-45 minutes) and wake up cranky. We spent more time trying to get her to sleep than she actually slept.

Difficulty Falling Asleep

The old tricks stopped working. Rocking, nursing, bouncing - she'd fall asleep and then wake up the moment we put her down. Or worse, she'd fight sleep entirely.

Increased Fussiness

An overtired baby is a cranky baby. She was irritable during the day because her sleep was so fragmented.

What Worked for Us

1. Optimizing Sleep Environment

We made her room pitch black with blackout curtains. Even small amounts of light can signal "wake up" during light sleep phases.

• Complete darkness (we covered every LED light)
• Cool temperature (68-72°F / 20-22°C)
• White noise machine running all night

2. Consistent Bedtime Routine

We created a predictable 20-30 minute routine:

1. Bath (every other night)
2. Pajamas and fresh diaper
3. Feeding in dim light
4. Lullaby or book
5. Into crib drowsy but awake

The consistency helped her brain recognize "sleep is coming."

3. Wake Window Management

This was a game-changer. At 4 months, optimal wake windows are about 1.5 to 2 hours. We'd been keeping her up too long, making her overtired.

Signs she was ready for sleep:

• Yawning
• Rubbing eyes
• Looking away, less engaged
• Getting fussy

Catching these early cues made a huge difference.

4. Gradually Changing Sleep Associations

We realized she could only fall asleep while nursing. When she woke between sleep cycles, she needed the same conditions to fall back asleep.

We gradually worked on putting her down slightly more awake over time. Not cold turkey - just small shifts. It took weeks, not days.

What Didn't Work

Adding Formula

Well-meaning relatives suggested she wasn't sleeping because she was hungry. Adding formula before bed made no difference - it's a developmental change, not hunger.

Later Bedtime

We tried keeping her up later, thinking she'd be more tired and sleep better. Wrong. An overtired baby sleeps worse. Earlier bedtime actually helped more.

Cry-It-Out at 4 Months

Some suggest full extinction sleep training. We weren't comfortable with this at 4 months - she was still young, and research suggests gentler methods work well at this age. We saved more structured sleep training for later.

How Long Did It Last?

For us, the acute phase lasted about 4 weeks. But here's the truth: the sleep changes are permanent. What improves is your baby's ability to connect sleep cycles.

Timeline for us:

• Week 1-2: Worst of it. Survival mode.
• Week 3: Slight improvement. Some longer stretches.
• Week 4: Started seeing 3-4 hour stretches again.
• Week 5+: New normal established. Not perfect, but manageable.

Survival Tips

For Parents

• Take shifts: If you have a partner, divide the night
• Sleep when baby sleeps: Yes, this cliché is actually useful now
• Lower expectations: The house will be messy. That's okay.
• Ask for help: This is the time to call in favors

For Baby

• Focus on environment: Dark, cool, quiet
• Watch wake windows: Don't let baby get overtired
• Keep routine consistent: Even when it doesn't seem to work
• Be patient: This is developmental, not behavioral

When to Seek Help

Consider talking to your pediatrician if:

• Regression lasts more than 6 weeks with no improvement
• Baby is showing signs of illness
• You're concerned about baby's weight or feeding
• You're experiencing symptoms of depression or extreme exhaustion

The Light at the End of the Tunnel

I know it feels endless right now. But looking back, those 4 weeks are just a blip in our parenting journey. The regression ended. Sleep improved. We survived.

And you will too. This too shall pass.