Parents should resist the urge to rush to the cotside when their baby cries at night, say experts. Instead, they say, children should be left to soothe themselves back to sleep.
Researchers asked more than 1,200 parents 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 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, published in the journal Developmental Psychology, babies move through a sleep cycle every one-and-a-half to two hours, where they briefly wake before nodding off again.
Professor Marsha Weinraub, from Temple University, Philadelphia, who led the study, said: "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."
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.
She 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."
During the study, the patterns of night time sleep awakenings of 1,200 infants aged six to 36 months were measured.
The researcher added that the link between mothers feeling depressed and their babies waking is another area that would benefit from further research.
One theory is that mothers who are depressed at six and 36 months may have been depressed during pregnancy- and this prenatal depression could have affected the baby's neural development and sleep awakenings.
But it's also important to recognise that sleep deprivation can, of course, exacerbate maternal depression, she said.
This research was funded by the National Institute of Child Health and Human Development, part of the National Institutes of Health (NIH).