The first year of your baby’s development is marked by rapid growth and transformative development. It can often feel as though every 4-6 weeks brings new sleep problems and another “regression” to navigate. Of all the developmental milestones your little one will encounter in the first year, the maturation of their sleep cycles, which occurs around 4 months old, is the only one intrinsically linked to sleep. While other milestones might indirectly influence sleep patterns due to cognitive and physical growth, this particular change directly shapes your baby’s sleep stages, cycles, and the balance of sleep hormones.
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In popular discussions and many parenting forums, the 4-month sleep regression is frequently painted in a negative light, but we challenge that perspective. With myriad blogs and books cautioning parents about this period, it’s easy to approach it with trepidation. However, we encourage a shift in perspective: see it as a celebratory milestone. For many, the term “sleep regression” implies a setback, but the truth is, your child is making monumental strides in their development. A more fitting term for this phase might be the ‘4-month sleep progression’ or ‘4-month sleep evolution’.
In this blog, we’ll explain the science behind this sleep phase, highlight its signs, discuss its duration, and offer tips to support you and your baby as you navigate this important milestone.
As your baby’s brain grows, their sleep patterns undergo significant changes. Initially, a newborn’s sleep is primarily characterized by two stages: REM (Rapid Eye Movement) sleep, which is associated with dreaming, and non-REM or deeper sleep. However, around the 4-month mark, your baby’s sleep patterns begin to resemble that of adults, with multiple stages of sleep—both REM and non-REM.
One of the most significant changes during this period is the establishment of the circadian rhythm. This internal clock helps regulate sleep-wake cycles, aligning them more closely with day and night. As a result, your baby starts to have a more predictable pattern of daytime wakefulness and nighttime sleep.
As your baby grows, their sleep cycles evolve. In the early months, each cycle for infants can be as short as 50 minutes. Over time, these cycles gradually lengthen. By around 3 years old, your child’s sleep cycles will approach the adult duration of approximately 90 minutes. At the end of each cycle, there’s a brief period of semi-awakening. These brief wake-ups serve a crucial evolutionary function: they allow the individual, whether baby or adult, to momentarily check their environment and ensure it’s safe before transitioning to the next sleep cycle. While adults often roll over and return to sleep, babies may have varying abilities to do so without external assistance, which can help explain why your little one may be restless and having a hard time staying asleep.
Within the realm of sleep training, the term “linking sleep cycles” describes the ability of a baby to transition smoothly from one sleep cycle to the next. It’s common to hear discussions about babies needing to “learn” to link these cycles, especially when they face challenges in doing so. While this terminology is widespread, it’s essential to delve deeper into what it truly means. Sleep cycle progression is fundamentally a natural physiological process. It’s not something that can be “taught” in the way we teach skills like tying shoes or reading. However, we can certainly guide and support babies in their natural sleep journey. The ability to self-soothe and transition between sleep cycles without fully waking is influenced by a myriad of factors, including sleep associations, environment, caregiver interaction, and individual temperament.
Concurrently, there’s a shift in the hormonal balance that governs sleep. Melatonin, often referred to as the “sleep hormone,” plays a crucial role in signaling to the body that it’s time to rest. On the other hand, cortisol, while commonly known as a “stress hormone,” has another essential function: it helps us wake up and stay alert. As your baby’s sleep matures, the production and regulation of these hormones become more defined.
Many parents can be caught off guard by the 4-month sleep regression. It’s not uncommon for a 3-month-old to start sleeping for longer stretches during the night, so it comes as a surprise when suddenly that same little one starts waking up every 1-2 hours throughout the night again. The abrupt change is a primary indicator that your little one has hit this developmental milestone.
Here are some other signs to watch out for:
It’s worth noting that these signs primarily relate to nighttime sleep. At this age, short naps are still very normal. So, if your baby’s naps seem brief, it doesn’t necessarily indicate they’re going through the 4-month sleep regression.
The 4-month sleep regression is significant, and like all developmental milestones, the duration of the sleep disruptions it brings can vary from one baby to another. While some might breeze through this phase with minimal disturbances, others might experience more pronounced changes in their sleep patterns. Not all babies will show overt signs of this sleep regression, but it’s important to note that they all undergo this developmental transition. Some might just internalize or process it differently, leading to minimal observable changes in their sleep patterns.
The 4-month regression can be a challenging time for both parents and babies. However, with a blend of understanding and thoughtful strategies, this period can be navigated with grace and confidence.