Parents should resist the urge to rush to comfort their baby when it cries at night, instead, infants should be left to soothe themselves back to sleep, experts say.
In a new study, researchers asked parents of more than 1,200 infants about their children's sleeping habits and found that by the age of six months there were two distinct groups.
While two-thirds slept through the night, a third woke up at least once a night, the 'Daily Mail' reported. The majority who failed to sleep through were boys, more likely to be breastfed and had mothers who were more likely to be depressed and have greater maternal sensitivity.
According to the study, babies move through a sleep cycle every one-and-a-half to two hours, where they briefly wake before nodding off again. "When mothers tune in to these night time awakenings then he or she may not be learning how to self-soothe, something that is critical for regular sleep," Professor Marsha Weinraub, from Temple University, Philadelphia, who led the study, said.
She said the research supported the idea that infants should be put to bed at a regular time and are best left to fall back to sleep of their own accord. "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," she said.
"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," she said. During the study, 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," Weinraub said.
"Some of them do cry and call out when they awaken, and that is called 'not sleeping through the night'," Weinraub added. Her team asked parents of more than 1,200 infants to report on their child's awakenings at 6, 15, 24 and 36 months.
They 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. However, a full 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, found the study published in the journal Developmental Psychology.