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What is the 4 month sleep regression?

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A few months into parenthood, and you’re finally hitting your stride. Your baby’s nap routine is on point, they’re going to sleep on their own, and sleeping (mostly) through the night. Then, out of nowhere, your 3-5 month old starts fighting naps, crying for you at bedtime, and waking all throughout the night. What gives? 

You guessed it: the dreaded 4 month sleep regression. Big changes are taking place in your baby’s brain, and it can take a serious toll on the whole family’s sleep. So if you find yourself up at 3am searching “What is the 4 month sleep regression?”, you’re in right place. 

Signs of the 4 month sleep regression 

When your baby is fussy and sleeping poorly, you may wonder if it’s teething, a growth spurt, an illness, or a sleep regression. It can be tricky to differentiate the signs. Most importantly, if your baby is running a fever (> 100.4​​°F for babies 3 months and up), call your pediatrician. Other signs of illness that warrant medical care are runny nose, cough, lethargy, diarrhea, or vomiting.

In contrast, signs of sleep regression are:

  • Fussiness
  • Resisting sleep
  • Frequent night wake ups 
  • Short naps

If your 3-5 month old is showing these signs, there’s a good change they’re going through their 4 month sleep regression. 

The science behind the 4 month sleep regression 

First, the good news: despite being called a “regression,” your baby isn’t going backwards! The 4 month sleep regression means that your baby is growing and developing as they should. This is an exhausting period of rapid growth and learning, but it’s a temporary phase. Let’s look at the science behind the 4 month sleep regression.

The 4 month sleep regression is all about babies transitioning out of newborn sleep patterns. For the first 3 months or so, newborns need 14-17 hours of sleep per 24 hours. They wake frequently to eat, and drop readily back into light (REM) sleep. 

All of that starts to change as your baby approaches 4 months old. Each baby’s brain develops at their own rate, but the transition out of newborn sleep happens for most babies between 3-5 months. This is the time when you’ll start noticing signs of the 4 month sleep regression. 

As babies’ brains grow, they begin to develop more nuanced sleep phases (like kids and adults). Instead of dropping quickly into and out of REM (Rapid Eye Movement) sleep, they cycle through lighter and deeper phases all throughout the night. 

The tricky part is, in between those different sleep phases, babies may wake briefly. This isn’t typically a problem if they’re accustomed to falling asleep on their own, and they have good associations with their safe sleeping space. With proper sleep conditioning from day one, many babies simply wake up for a few moments, notice that they are safe in their comfortable crib or bassinet, and settle back down to sleep. 

However, if your baby fell asleep somewhere other than where they woke up (like your arms), waking up in their crib alone may startle them. This is why babies going through their 4 month sleep regression will fuss and cry out after being asleep for only 30-50 minutes: they’re simply in between sleep phases, and they’d like to let you know about it. 

How to manage the 4 month sleep regression

The best way to manage the 4 month sleep regression is to practice sleep conditioning from birth. That means setting up a proper safe sleep environment and always putting your baby down in their crib or bassinet when they’re drowsy, but still awake. Sleep conditioning teaches babies to fall in love with their independent sleep space and that they don’t need a parent’s help to drop off to sleep. 

However, for some babies this is easier said than done. If you haven’t practiced sleep conditioning during the newborn phase, the 4 month sleep regression may be harder for you and your baby, but you will still get through it! This can be a period of 2-4+ weeks when you have to hold the course and help your baby learn to self soothe so that they don’t need to cry out for you in between sleep cycles. The key is to help them get as much sleep as they need without developing (or prolonging) bad sleep habits:

  • Establish a consistent bedtime and nap routine
  • Encourage baby to fall asleep independently (no rocking or feeding to sleep)
  • Do not let your baby become overtired
  • Keep the room dark, cool (68°F-72°F) with white noise
  • Practice “the pause” – wait a moment before going to your baby when they fuss during sleep, they may be simply settling on their own
  • Stay consistent!

The bottom line 

When your baby is showing signs of the 4 month sleep regression, they’re telling you that they are developing new sleep needs. If previously you’ve been able to allow your baby to nap on the go, stay up late at night or feed them to sleep, it’s tempting to stick to these habits from the newborn phase. But by 3 months, your baby will really start to develop sleep crutches that are hard habits to break long term. Help them avoid this by watching wake windows to prevent overtiredness, sticking to consistent bedtime and nap routines, and giving them a chance to fall asleep on their own. When your baby wakes after a short time during their 4 month sleep regression, don’t rush in to pick them up. Give them a chance to settle, and if needed, try to soothe them back to sleep without picking them up or feeding them.

Finally, you don’t have to go through this alone! The 4 month sleep regression can be extremely hard on parents. Many are going back to work, transitioning from the bassinet to crib, or transitioning out of the swaddle all during this phase. We’re here to help with newborn sleep conditioning and professional sleep training for babies 5 months and up.