What is the 4 month sleep regression?
The 4 month sleep regression
I often hear parents throwing around the phrase “sleep regression” and wondering if the “X month regression” is the reason their baby isn’t sleeping through the night. Most regressions are attributable to either illness, teething, or milestone developments – be they physical, cognitive, or social-emotional – and should resolve themselves within a week or two assuming your little one had good sleep skills to begin with. However, there is one regression that is different from the rest as it is the only true biological regression and a total reorganization of the body and the brain. That, my friends, is the four-month sleep regression.
The science behind the 4 month sleep regression
We all sleep in stages ranging from light to deep and these different stages make up a “sleep cycle” that we transition through several times each night. When babies are born, their sleep is drastically different from the sleep of adults. Newborns really only have TWO stages of deep sleep whereas adults have FOUR stages ranging from very light to very deep. Because your newborn sleeps so deeply, it is easier to transfer them from your arms to a bassinet without waking them, and to keep them sleeping in all types of situations. When your baby undergoes the biological shifts that occur around four months, they “graduate” from the two-stage cycle they were born with to a four-stage cycle that they will follow for the rest of their lives. Why is my good sleeper suddenly up all night long? With the shift to a 4-stage sleep cycle, babies are no longer “sleepy newborns” and are spending more time in lighter stage of sleep. (Note: light stages of sleep are equally important parts of the sleep cycle as deeper stages of sleep. REM sleep – where the brain is consolidating information and storing memories – is one such critical light stage of sleep.) Naturally, spending less time in deep sleep means that there is more potential to be woken both from environmental factors (like surrounding sounds or light) and natural occurrences (like the biologically normal “partial wake up” period between sleep cycles.) In between sleep cycles, there is a period where we all “come to the surface” of sleep and this brief awakening is one that we don’t remember the next morning as long as certain comforting truths are in place: we are in our beds, it is still dark out, and we have hours to sleep until morning. These periods of transition are so brief and so benign, that we have no conscious memory of them when we wake the next day. Infants experience similar sleep patterns and will “come to the surface” of sleep just as often as we do as adults. But let’s say you nursed (or rocked, or held, or cuddled) your little one to sleep and put them down in their crib once you were sure they were deeply in dreamland. When they later awaken between their cycles, even briefly, chances are you are no longer nursing them (or rocking, or holding, or cuddling them). Suddenly, they are in a situation that is vastly different than the one in which they fell asleep. This is no doubt going to be startling and cause a full-blown wake-up instead of a simple transition into another sleep cycle. Also happening around this time is a cognitive surge where infants become much more aware of their surroundings. That means that those infants who rely heavily on external strategies to fall asleep (nursing, rocking, bouncing, etc.) are more likely to protest when those things are absent during the night. They strongly believe they need those specific circumstances to be able to make sleep happen for themselves. Up until now, you could have been sailing through, rocking your baby to sleep and everything had been fine. But, if your little one believes they need certain circumstances to fall asleep, these developmental changes can cause major problems.
But the 4-month regression isn’t all bad! In fact, it’s a time of huge opportunity. Your baby now has a more mature circadian rhythm and biological clock; they are now capable of sleeping longer stretches because they can go longer between feeds; and they can now follow a more appropriate sleep-wake schedule. The possibilities are endless.