When a baby sleeps well most of the time, but wakes once for a long period overnight - typically for 1-3 hours - this is referred to as a split night. Usually any attempts to help them fall back to sleep won't work, and they'll either be happy and alert or upset and seemingly frustrated with your attempts to settle them.
It’s not considered a split night if your child is waking frequently for short periods through the night. (Read about sleep cycles and the the 4 month sleep regression here).
A split night occurs when the two body systems that govern sleep - the circadian rhythm and the homeostatic sleep drive - fall out of sync.
The circadian rhythm is our internal body clock and refers to our tendency to sleep, wake and feel alert at roughly the same times every day over a 24- hour cycle.
The homeostatic sleep drive refers to our body’s increasing need for sleep the longer we are awake. This sleep pressure builds up over the day and helps us fall asleep for the night. By morning this pressure has worn off and our need for wakefullness takes over.
When these body systems are working in harmony, your baby will gradually build up sleep pressure over the day, fall asleep at bedtime and then stay (mostly) asleep through the night, and wake at a regular time in the morning.
When a split night happens, sleep pressure drives separately from the circadian rhythm. Making a baby fall asleep at bedtime, but after several hours they wake feeling refreshed and alert as if ready to start the day! And it’s not until the circadian rhythm kicks back into gear are they able to fall back to sleep.
So how do you fix a split night?
There are a few reasons why a split night might be happening, but the most common and easiest to fix - is a scheduling issue. Babies need to have the ideal sleep pressure built up over the day to be able to sleep soundly at night. Too many short naps, or their naps are at the wrong times of the day can all contribute to a bad night.
Our baby & toddler nap and feeding routines can help solve your sleep troubles.
We have age-appropriate routines available to follow from birth to 3 years, and have the ideal balance of awake time and nap timings to foster great nights. 5 Star Reviewed.
"I’m so shocked at how much this guide has changed my little guys sleep. And so quickly. I’m so relieved he is getting a full nights sleep and amazing naps, good sleep is so so important and I’m so grateful!" Janeece, G, Perth Australia
Read also: when to stop following wake windows and switch to a routine by the clock.