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Updated: Oct 23, 2022

The Science Behind the Four-Month Regression and Tips to Get Through It

The four-month regression is a buzz-word in every mom group. "Your baby is 3 months old? Oh be careful- the 4-month regression is coming!” “Ugh, my baby is in the 4-month regression. We are getting zero sleep at night!” “Sounds like your baby is going through the 4-month regression. It’s brutal!” But what is this dreaded phenomenon? Why is your baby sleeping worse all of a sudden? And how do you make it out the other side alive?

The Science Behind the Four-Month Regression

Okay let’s geek out for just a minute. In order to understand what your baby is going through you will need to know a couple of things…namely, what newborn vs. infant sleep cycles look like, and what sleep props and sleep associations are.

When your baby was a newborn she only had two stages of sleep: Active (REM) sleep, and Quiet (Non-REM) sleep. Newborns spend 50% of their time in each stage.(1) A newborn in quiet, deep sleep is very difficult to arouse. So if your newborn is having a good sleep day, you can bet on about 25 minutes of active REM sleep and 25 minutes of deep sleep where the baby doesn’t make a peep.(7) Then hopefully your newborn will start from the beginning 2-3 times during one solid nap. You are able to rock, hold, or feed your newborn to sleep and place your newborn down at just the right time where she stays in that deep sleep. These external methods of soothing a baby cause an association that forms between that support you give her and sleep. The methods that we use to help a baby to sleep are called sleep props. When your baby is first born, use all the sleep props to your advantage! Around three to four months old a newborn’s sleep cycle shifts to five stages of sleep. (Some say four, some say five!)(8) These five stages are as follows: Non-REM sleep which includes drowsiness, light sleep, deep sleep, and very deep sleep, as well as REM (active) sleep.(8) Because the infant’s cycle is broken up into five distinct stages, the baby spends less time in each stage to equal one full cycle. Since the infant spends more time in lighter stages of sleep than a newborn, it is much easier for the infant’s sleep to get disrupted and cause the baby to wake from sleep prematurely. If an infant who has transitioned to a five-stage cycle is dependent on something external to fall asleep, then this infant will have difficulty going through those lighter stages of sleep in order to get to the deeper sleep. The startle reflex will abruptly awaken her, light or sound might disturb her sleep, and a rumbly belly will be more of a distraction for the infant. If the baby cannot start the sleep journey out on her own (which remember is “drowsiness”), then she will struggle to pass through these other four stages of sleep without a disruption.(3) Society has labeled the transition from a newborn two-stage cycle to an infant five-stage cycle the “Four-Month Regression”... “regression” because infants who were napping during the day and sleeping decently at night have switched all of a sudden to frustrating 10-15 minute micronaps all day, or wakings every 3 hours at night.

Now that you are a pro at baby sleep science, let’s dive into how to avoid the 4-month regression, as well as how to get back on track once the regression has hit your household like the Spanish Flu of 1918.

How Do I Avoid the Four-Month Regression?

Parents who inquire about my services before four months of age always ask one of two questions: “Will sleep training now help me avoid the 4-month regression?” or “Will all my hard work of sleep training be undone when my baby goes through the 4-month regression?” And the answers are simple: Yes, and Nope. As we established already, the regression in sleep is caused by your baby not knowing how to start the sleep journey out on her own, thus not knowing how to pass through each stage of sleep on her own, completing one cycle and going into the next cycle.(2) If you teach your baby how to fall asleep independently without the help of anything external, such as a pacifier, feeding, or rocking, then she will be able to handle this change in sleep cycles like a champ because she has the self-soothing skills needed to pass through the lighter stages of sleep.

How Do I Get Back On Track if My Four-Month Old’s Sleep Goes South?

If you have decided to hold off on sleep training until your baby is a little older you may see sleep go from “eh, I can hang on a little longer,” to “Oh dear God… someone help me!” around the 3-4 month mark. When this happens parents often are kicked into survival mode, doing anything for a few extra hours of shut-eye. Unfortunately this increase in assistance causes the effects of the four-month regression to stick around. I often hear parents of six-month olds or nine-month olds tell me, “My baby slept great until 4 months old. Then their sleep just kept getting worse and worse.” Once your baby’s sleep develops to a permanent five-stage cycle and a baby’s brain creates strong external associations with sleep, an infant will not typically spontaneously learn the skill of self-soothing and independent sleep, as studies have shown that the parental involvement of settling the baby correlates to poorer night time sleep.(4)(5) Of course they say that all children learn to sleep. But it’s a matter of when that happens and I don’t really want to wait around for it to happen! There is something you can do to climb out of the pit you may have fallen into around four months old. If you teach your baby how to fall asleep independently, free from the association of a pacifier, a swaddle, rocking or feeding, then her body can cycle through these stages of sleep on her own, thus consolidating her sleep, and lengthening the nights and naps. Sleeping through the night of course is dependent on your baby not being hungry, but around 4-6 months old a baby often weighs enough (over 12 lb.)(6) and takes enough calories in during the day to drop her feedings on her own, if she can emerge from a sleep cycle and go into another cycle when hunger is not present. In my infant plans under 6 months old I teach the parents how to get their infants sleeping 10-12 hours overnight without “cry-it-out”, or refusing to feed their baby at night. It’s all about creating positive reinforcement around sleep and removing the sleep associations that hinder sleep. Three to four months old is a wonderful time to teach this lifelong skill to your baby so that you can get back on track with shut-eye at night and predictable naps during the day.

My Baby Is Sleep Trained But All of a Sudden Not Sleeping Well!

If your sleep-trained baby does have a rocky week or two most likely all you need to do is revamp her schedule, dropping the fourth nap and increasing awake times/decreasing daytime sleep. A typical four-month old is awake between 2 and 2.5 hours before nap/bedtime, and has four hours of daytime sleep split between three naps. If your sleep trained baby is chugging along on 90 minute wake windows and BAM- all of a sudden she is taking short naps, fighting bedtime, or waking again in the middle of the night then adjusting the daytime schedule can get you right back on track.
Your three to five month old may also go through a short disruption in sleep when he learns how to roll from back to side or tummy. This developmental milestone occurs between four and six months of age.(8) Avoid playing the “roll the baby” game all night. Let your baby stay in whatever position he got himself in, offering reassurance in intervals if he is upset about this. Your baby will learn to feel comfortable on his back, tummy, or side as long as you allow the time and space to let him work it out. Rest assured that the AAP safe sleep guidelines allow for tummy sleeping if the baby puts himself in that position on his own, and the Sleep Foundation says to, "simply begin each night with the child sleeping on their back and in a safe sleep environment free from blankets and other soft or loose objects," (9) then your baby can get into whatever their favorite position is on their own.

Don’t Want to Wait Out the Storm?

I offer two types of sleep training methods and lots of individualization within those methods during my one-on-one two-week sleep program. Book a FREE 15-minute phone assessment here so we can chat more about how we will work together to reach your goal of a “regression-proof” independent sleeper.


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