New parents can relax: Research suggests it's normal for infants' sleep patterns to vary widely.
"Although previous research has shown that infants start sleeping through the night at different stages of development, little is known about individual sleep patterns night after night," explained study leader Marie-Helene Pennestri. She's an assistant professor in the department of educational and counseling psychology at McGill University, in Montreal, Canada.
Many new parents expect their baby to start sleeping through the night by about 6 months of age, but Pennestri and colleagues found there's no firm timeline.
For the study, the researchers asked the mothers of 44 infants who were 6 months old to keep a sleep diary about their children for two weeks. The results revealed significant variations in the infants' sleep patterns, not only for different babies, but also from night to night for the same baby.
On average, infants slept six hours consecutively for about five nights out of two weeks, and eight consecutive hours for about three nights during that time. But half of the infants never slept eight hours consecutively, according to the study published in the December issue of Sleep Medicine.
Some parental practices appeared to affect infant sleep patterns. For example, breastfeeding and co-sleeping were associated with more variation in night-to-night sleep patterns.
But while that finding is consistent with many studies, other factors could be at play, the authors suggested. The researchers said that mothers who are breastfeeding and co-sleeping are more likely to be aware of their infant's night awakenings.
"Parents are often exposed to a lot of contradictory information about infant sleep. They shouldn't worry if their baby doesn't sleep through the night at a specific age because sleep patterns differ a lot in infancy," Pennestri said in a university news release.
"One important piece of the puzzle is understanding parents' perceptions and expectations of infant sleep. In future research, we hope to explore what 'sleeping through the night' really means to them," she said.