Newborn babies sleep a lot, and that’s an understatement. Expect your baby to be asleep for up to 18 hours over the course of 24 hours in his first few weeks, but in spurts of 1-3 hours at a time - babies generally wake up in between for their feeds.
From zero to six weeks, a baby’s sleep cycles are far shorter than yours. He or she will spend more time in rapid eye movement (REM) sleep, which is a light, easily disturbed sleep, and less time in non-REM or deep sleep. This is necessary for the changes that are happening in his brain. This is when that cute twitching, smiling, or eye-fluttering occurs. Professor of Medical Sciences at Washington State University, Marcos Frank, found that REM sleep helps growing brains adjust the strength or number of their neuronal connections to match the input they receive from their environment. He further said that young brains, including those of human children, go through critical periods of plasticity - or remodeling - when vision, speech, language, motor skills, social skills, and other higher cognitive functions are developed. Effectively, REM sleep is when the baby’s development takes place.
While children sleep, a growth hormone called ‘somatotrophin’ is dispersed through the pituitary gland. Although this hormone is released throughout the day, approximately 80% of it is released soon after a child or adolescent is in the Non-REM stage of sleep. So if a child does not reach the optimum levels of both REM and non-REM sleep requirements at night, it can subsequently inhibit their physical development.
Once he is between six weeks and eight weeks, your baby will probably sleep for shorter spells during the day, and longer periods at night. However, he'll still wake up to feed– that means more deep non-REM sleep, and less light (REM) sleep.
The pattern may break as early as eight weeks old, and your baby may start to sleep through the night. But remember, every baby is different, so prepare to be interrupted for at least the first few months. If your aim is to get junior to sleep through the night, encouraging clear habits from the start will help!