The lowdown on sleep cycles and wake windows

_english baby sleep naps sleep coaching sleep cycles sleep training wake windows Nov 12, 2020

Today I answered Sandy's questions about sleep cycles and wake windows. Both are crucial to know about when you want to sleep coach or sleep train your baby!


Hello everyone, it's Anna. Thank you so much for tuning in today. You are listening to The Baby Sleep Project Show: The place to learn about baby sleep and sleep coaching.
Today I'm going to answer questions from Sandy. Sandy sent her questions to me in email. And if you would like your questions to be answered on my show, then send them to me at [email protected]. So Sandy sent me quite a lot of questions and I'm not sure I will be able to answer all of them, at least not in one episode. But I tried to group these questions into topics, so it makes more sense for the show. So the first topic is sleep cycles. The first question goes like this: "Why does baby sleep for a few hours and then suddenly cry. After crying for 10 minutes, he sleeps again".
So to answer this question, first, I would like to read an excerpt from The Baby Sleep Book, because to understand why this happens, you need to know about sleep cycles. So... "Sleep is not a homogeneous state. It has different phases, which alternate during the night, and each has its own differentiating characteristics, like different brainwaves, muscle movements, muscle tone, eye movements, heart rate, and breathing rate.
Basically, adult sleep is divided into REM (which stands for rapid eye movements), so REM sleep and non-REM sleep. Non-REM sleep is further divided into four stages. When you fall asleep, you first enter stage I of non-REM sleep. This is drowsiness, which represents a transition from wakefulness to sleep. Stage II is light sleep, from which you can wake up easily if you, for example, hear your name. If no one wakes you up, you go deeper into stage III and IV, which is deep sleep (sometimes also called slow wave sleep). In deep sleep you lie quietly, your breathing rate and heart rate is regular, your muscles are very relaxed and it would be difficult to wake you up. Deep sleep is responsible for most of the restorative properties of sleep. The body repairs, muscle and tissue, boosts your immune system and produces growth hormones in this state.
Sometimes you go back and forth between non-REM stages before you enter the first REM phase, or you go straight from the first deep sleep phase to the REM phase. In REM sleep your brain is much more active than in non-REM sleep. And this is when dreams occur... Your breathing and heart rate are irregular and you move your eyes rapidly under your lids (hence the name). You cycle between REM and non-REM sleep for the rest of the night. A sleep cycle consists of one period of non-REM sleep and one period of REM sleep... Everyone tends to wake up briefly after dreaming episodes, however, you rarely remember it. You turn, adjust your pillow and check the environment. If everything is okay, you go back to sleep within seconds... The problem is, babies tend to wake up more between sleep cycles than adults, plus, their sleep cycles are shorter, so they wake up more often too". The other problem is that babies sometimes don't know how to go back to sleep after they wake up between sleep cycles.
Okay, so this is as far as the quote goes. So most babies don't wake up after every single sleep cycle. In general, the first few hours of the night, sleep is deeper and most babies don't wake up. Even when they do, sometimes they go back to sleep independently, without a peep, so you might not even notice it. But about five hours after going to bed, sleep gets lighter and babies tend to wake up more often between sleep cycles.
So what happens is that in the first few hours, after going to bed, your baby is in deeper sleep and he doesn't wake up between sleep cycles. But after that, he wakes up and he needs some time, you said 10 minutes, before he can go back to sleep. It might be difficult for him, he might not have a routine how to go back to sleep. And that's why he cries. If you want to help your son to go back to sleep more easily, the key is to try to make sure that the circumstances are similar in the middle of the night to those when he fell asleep for the night in the first place. So basically, when your son goes to bed at bedtime, how does he fall asleep? What are the circumstances? Try to... Whatever method you choose, whether your baby falls asleep with your help, or whether your baby falls asleep independently, whether your baby falls asleep in his crib, or whether your baby falls asleep in the parental bed. Try to make sure that in the middle of the night, the circumstances are the same, because it will help him go back to sleep.
You can imagine that if he wakes up in the middle of the night and suddenly he is in a different bed, or maybe he fell asleep in your arms, and now he is in his cot, that is confusing and even frightening for a baby. So whatever sleeping arrangements you have, try to keep them consistent throughout the night. And that will help him go back to sleep. Okay.
Second question in this topic is the following: "What is the difference when baby wakes up 30 minutes versus 45 minutes after a nap?" Okay. So the difference is basically just the length of the sleep cycle. So it seems that during thisnap, your baby only has one sleep cycle and the length of sleep cycles varies. So for adults, the length of a typical sleep cycle is between like 90 to 110 minutes. So one and a half to almost two hours, but it is shorter in kids and infants.
So by the time the baby's about one year old, the sleep cycle is around 60 minutes long while at two years of age, it's about 75 minutes. And by six years of age, it is about 90 minutes, but I assume your baby is younger than one year old. So that's why the sleep cycles are shorter. And a little variation in length is absolutely normal. Sleep cycles don't work like clockwork. So it means that his sleep cycle is 30 to 45 minutes and (then) he wakes up. The other thing is that it might be possible that he needs more than one sleep cycle for a nap. So maybe it would be better for him to sleep twice this much, or maybe three times this much. And what happens is that your baby just doesn't know how to link sleep cycles or how to fall back asleep after waking up between sleep cycles. But it depends, it... I will get to this in the next topic, because it depends, sometimes it's absolutely normal for a nap to be just 30 or 45 minutes.
The next topic is naps and schedules. First question: "My baby is on three naps. What is the ideal amount of sleep for the first, second and third nap? Trying to cap total daytime sleep at 3.5 hours". So Sandy, you didn't write how old your baby is, but based on what you've wrote, that he's on three naps and you are trying to cap total daytime sleep at three and a half hours, I assume that he's around six months of age, because different sleep charts and nap charts, and recommendations suggest that three and a half hours are recommended for six-month-olds to sleep during the day. And usually that is the age, when babies are on two or three naps.
So to answer your question, there's no set time for the length of naps... of individual naps. Total sleep for a 24-hour-period is limited. So there's, there's only so much sleep your baby needs during the whole day. And if he sleeps more during the day-time, then he will sleep less during nighttime. So it is wise to cap total daytime sleep. And if your son is six months old, then three, three and a half hours during the day is absolutely fine. What you can do, is that you let him sleep for the first and the second nap almost as long as he wants, probably it won't be longer than 3.5 hours, and you wake him up from his nap for the last nap, if it's longer than ideal. If you see that the total daytime sleep exceeds three and a half hours, and you know that this would affect his nighttime sleep and it's not ideal for your schedule, then you can wake him up from his last nap.
When you wake him up is important though, because it's best to do it between sleep cycles. As I have mentioned before, a sleep cycle consists of a period of non-REM sleep and a period of REM sleep. And it is easiest to wake someone up between sleep cycles, so after REM sleep periods. If you pay attention to your baby, you might be able to differentiate between the two types of sleep. In babies REM sleep is also called active sleep, while non REM sleep is also called quiet sleep. And it is because it is quite easy to visually distinguish between the two periods. And what you want to avoid is to wake your baby up from deep sleep. Okay? So I'm going to quote my book, The Baby Sleep Book again.
"If you watch your baby sleeping, you might be able to differentiate between active sleep and quiet sleep. In active sleep your baby might jerk, kick, make funny faces, smile, sometimes hold their breath for a few seconds, then take a very deep breath and you can see their eyes moving under their lids. They might even cry a little in their sleep. In quiet sleep, they lie very still, breathe regularly and move very little: only jerk, startle or make quick sucking motions occasionally".
So if you see that your baby is very still, his breathing is very regular, then it means that he's in deep sleep and it's best not to wake him up from deep sleep. Because first of all, it will be very difficult to wake him up. Second of all, he might be moody when he wakes up. So it's better to wake someone up from either active sleep or just after the active sleep period, which is of course difficult to know when it happens. But if you know how long a sleep cycle is for your baby, it seems that it's some... somewhere between 30 and 45 minutes now, then if you just go in after a period of time, when a sleep cycle is supposed to end, then if you just go in and watch your baby for a few minutes, then you will be able to tell whether he's in quiet sleep or active sleep. And if he's in active sleep, that means that it is probably the end of the sleep cycle, since you timed the time he was asleep, so you can safely wake him up. Okay.
Second question: "When is the appropriate time to lengthen a wake window and which wake window is easier to lenghten first? How do you know which wake window is causing any night wake ups?" Okay. So these are actually three questions about wake windows. So I'm going to answer the first question first. So when is the appropriate time to lengthen a wake window? Okay. So for six months old babies, the wake window is usually between two to three hours and six months old babies usually take two or three naps. For nine months old babies the wake window is usually somewhere between three and four hours and they usually take one or two naps. Okay.
So if I'm assuming, right, and your baby is somewhere between six and nine months then it's absolutely okay to lengthen the wake window. And that leads to your second question: which window is easier to lengthen first or which nap to drop? Well, it depends on your baby. So if you observe your baby for a few days and you see that it is difficult for him to go to sleep during one of his naps, maybe it's the morning nap, maybe it's the middle nap, or the afternoon nap, then I would try to push that nap a little bit later and eventually I would try to drop it.
And when you drop that nap, then you will see that nighttime sleep will probably increase. So you will have to adjust bedtime a little bit. So make it earlier. And of course you will have to adjust the timing of the other two naps too. So try to distribute the naps throughout the day, more or less evenly. But you know your baby! If your baby is more sleepy in the morning, then it is completely okay for the first nap to be closer to wake up time, so for that first wake window to be shorter than the afternoon wake window. Or if your baby is sleepier during the afternoon, then it is of course, okay to have a shorter afternoon wake window.
And the third part of your question was how do you know which wake window is causing any night wake ups? Well, the answer is that wake windows do not really cause night wake ups. Okay? So it is possible that if your last wake window is too short, meaning that your baby wakes up too late from his last nap, and that nap is too close to bedtime, that it will be difficult for your baby to fall asleep at bedtime, because he's just simply not sleepy enough. But a wake window in itself wouldn't cause night wake ups. I mentioned earlier that we tend to wake up between sleep cycles, so we wake up between sleep cycles. It's absolutely normal. What you have to teach your baby is how to fall back asleep independently between sleep cycles. Because once they learn that they will fall back asleep quicker.