I bring this up because my friend was wondering why her baby was able to sleep soundly for 4 hours at the beginning of the night, but would wake up every 2 hours after that.
Quite simply, the beginning of the night is when you get the most restful and deepest sleep (there is a greater amount of deep sleep, called N3, earlier in the sleep cycle). We all wake up several times a night, but during this stage it’s much easier for a baby to “konk” out and keep sleeping.
However, for the rest of the night, a baby sleeps very lightly. Falling back asleep on their own becomes increasingly difficult when their sleep shifts into light, REM sleep.
And that’s why they wake up so easily at the crack of dawn. Or sometimes, pre-dawn. I found my baby would wake up at 5am if he was over-tired and went to bed too late. You’d think he would want to sleep in! In these cases, I think his body and brain were “irritated” that they didn’t get enough of that deep sleep early in the night.
That’s why it’s important to tuck them in early. They get the best quality, most restorative sleep early in the night.
Personally, I found the bedtime sweet spot to be between 7:30pm and 8pm. Anytime later makes getting to sleep and staying asleep much more challenging.
(Sure I know a baby who sleeps from midnight to noon, but there are exceptions for everything. In such cases, usually very young babies, they need to adjust their circadian rhythm… in other words, learn to sleep at night and stay awake during the day. See here for more info.)
Take heart! In my experience, as the baby gets older, you get longer stretches at the beginning of the night.