What you need to know: the ‘Basics’

  • Biological processes that are not under parental/external control are the most basic and influential determiners of how your baby sleeps, and if you can understand and work with these, you will be well on your way to great sleep habits.
  • Circadian rhythms, or your baby’s ‘biological clock’, begin to emerge between 6 to 12 weeks. This is intrinsically connected to your baby’s homeostatic sleep drive.
  • Homeostatic sleep drive means that the longer your baby goes without sleep, the longer he will subsequently sleep, and conversely, the longer he’s been asleep, the more the pressure to sleep dissipates, and the more likely he is to wake.
  • A baby’s sleep cycle lasts for 45 to 50 minutes, with the first 10 to 20 minutes or so being the lightest sleep phase, so you may need to spend at least 20 min settling your baby through the light sleep phase into a deeper sleep. This can explain a wake up after the 15 to 30 min mark or a short 45 min nap, and some babies have difficulty linking sleep cycles because they wake easily during the first stage of a cycle.
  • Sleep window times work alongside your baby’s biological needs as outlined above.
  • After about 12 weeks, the best sleep windows are between 9 to 10am, 12 to 2pm and 6 to 7pm.
  • Body temperature typically rises during the day and drops as the night progresses, and is at a minimum around six hours after the onset of sleep.

What is a circadian rhythm?

Our circadian rhythm is like our internal body clock, which is programmed and governed by light, darkness and food, as well as social interaction. It’s controlled by hormones, which are produced in a part of the brain located just above the optic nerve. Two of these hormones are melatonin and cortisol, which naturally fluctuate over 24 hours, and these can have a significant impact on your baby’s sleep. The hormone melatonin makes your baby feel sleepy, and conversely, cortisol can stimulate your baby. Your baby’s circadian rhythm works alongside her body temperature and homeostatic sleep drive to help him get the sleep he needs.


What is homeostatic sleep drive?

This is an internal biochemical system that operates as kind of a timer or counter, causing pressure to sleep. It effectively reminds the body that it needs to sleep after a certain time awake: the longer we have been awake, the stronger the desire and need to sleep becomes, and the more likelihood of falling asleep increases, and conversely, the longer we’ve been asleep, the more the pressure to sleep dissipates and the more the likelihood of awakening increases.

The diagram above shows the relationship between circadian rhythm (need for sleep) and homeostatic sleep drive. You can see the need for sleep and the sleep pressure increase after midday, hence a lunchtime nap is so important.
This diagram shows the rise and fall of cortisol and melatonin over 24 hours. You can see that melatonin rises at night when it’s dark and that cortisol peaks between 9am and midday and is lowest around midnight.

Baby’s Sleep Cycle

The diagram above shows the natural progression of a baby’s sleep cycle.