During the first three months of development, tiny babies rarely sleep for more than four hours without requiring feeding. At around three to six months, the majority of babies start to settle. They are awake for longer periods during the day and some with lucky parents may sleep five-hour stretches at night! The time they spend in deep sleep starts to lengthen and the time spent in light sleep shortens (Ficca et al, 2000). This means babies are able to enter deep sleep more quickly. This is called sleep maturity. (Sears, 2005).
The time your baby takes to reach sleep maturity may vary and even when she does reach it, she may still wake up regularly. This is because by the time she is old enough to reach sleep maturity (usually towards the end of the first year), uncomfortable and painful stimuli present themselves, such as colds and teething pain. Furthermore, separation anxiety develops at around this age which causes sleeping problems. Babies also start reaching developmental milestones, such as sitting, crawling, and walking which causes them to run through their newly acquired skills in their sleep (Lavin, Glaser 2007).
Ficca, G., Fagioli, I., & Salzarulo, P. (2000). “Sleep organization in the first year of life: Developmental trends in the quiet sleep-paradoxical sleep cycle”. Journal of Sleep Research, 9, 1-4.
W. Sears (2005). “The Baby Sleep Book: How to Help Your Baby to Sleep and Have a Restful Night.” Harper Thorsons.
A. Lavin, S Glasser (2007). “Baby & Toddler Sleep Solutions.” Wiley Publishing, Inc.