Rex
Parents have been advised to resist the urge to comfort their babies when they wake up crying in the middle of the night.
Instead of rushing to their cots whenever they stir, child development expert Professor Marsha Weinraub says the majority of infants are best left to self-soothe and fall back to sleep on their own.
Writing in the journal Development Psychology, the expert from Temple University in Philadelphia, said: "The best advice is to put infants to bed at a regular time every night, allow them to fall asleep on their own and resist the urge to respond right away to awakenings.
"By six months of age, most babies sleep through the night, awakening their mothers only about once per week. However, not all children follow this pattern of development."
During the study of 1,200 babies, the patterns of night time sleep awakenings of infants aged six to 36 months were measured. The findings revealed two groups: sleepers and transitional sleepers.
"If you measure them while they are sleeping, all babies - like all adults - move through a sleep cycle every 1.5 to 2 hours, where they wake up and then return to sleep," she said.
"Some of them do cry and call out when they awaken, and that is called 'not sleeping through the night'."
Professor Weinraub's research found that by six months of age, 66 per cent of babies - the sleepers - did not awaken, or awoke just once per week, following a flat trajectory as they grew.
But 33 per cent woke up seven nights per week at six months, dropping to two nights by 15 months and to one night per week by 24 months. Of the babies that awoke, the majority were boys.
The transitional sleepers tended to score higher on tests that assess a difficult temperament that identified traits such as irritability and distractibility.
And, these babies were more likely to be breastfed. Mothers of these babies were more likely to be depressed and have greater maternal sensitivity.
"Families who are seeing sleep problems persist past 18 months should seek advice," Professor Weinraub added.
What do you think? Did you try controlled crying?
More on Parentdish: Why controlled crying made me a better mother