It's one of the most common, and often frustrating questions moms of infants hear: "Is she sleeping through the night?" But new research from McGill University suggests parents shouldn't worry if their child doesn't reach this milestone by six months of age or even a year old.
The study, to be published in the December edition of the medical journal Pediatrics, found a large percentage of developmentally normal, healthy babies don't sleep through the night by a year old, and are not at increased risk for delays in cognitive, language or motor development as a result.
"If there was only one thing I could tell parents, it would be do not worry if your infant does not sleep through the night at six months of age," the study's lead researcher, Marie-Hélène Pennestri told NBC News.
Sleeping through the night, also known as consolidating sleep, was defined in the study as six to eight hours of uninterrupted sleep. At six months of age, 38% of typically developing infants were not yet sleeping six consecutive hours at night, and more than half — 57% — weren't sleeping eight hours. At 12 months old, 28% of infants weren't yet sleeping six hours straight at night, and 43% weren't staying asleep for eight hours.
So if your baby isn't sleeping through the night you are not alone, mama.
One of the biggest takeaways from the study is dispelling the notion that interrupted sleep in the first year could cause developmental problems. "In the present sample of typically developing infants, we were unable to find any significant associations between sleeping through the night at 6 or 12 months of age and variations in mental or psychomotor development," the study concluded.
The researchers gleaned information from a longitudinal birth survey of mothers and their babies and followed the babies until they were three years old. They looked at surveys of parents of 388 infants aged up to six months, then checked in with 360 of them at 12 months.
While sleep undoubtedly plays a fundamental role in child development, total sleep, including naps, might be more important than getting eight consecutive hours, the researchers wrote.
Child development isn't the only concern however when examining infant sleep patterns. Some parents may worry that lack of sleep increases their risk of developing depression. While it's true that sleep is critical for mental health, the researchers also found no direct link between how often babies woke at night, and the mother's postnatal mood, but rather that overall sleep plays a bigger role.
A mom who is able to catch up on sleep and nap during the day for instance, may be less affected by sleep deprivation even if she is up frequently through the night.
"Maternal sleep deprivation is often invoked to support the introduction of early behavioral interventions, but it may be that mothers' expectations about being awakened at night along with the total number of hours they sleep over the course of a day are better predictors of maternal well-being," the study's authors wrote. "It is something that will need to be considered in future studies."
While it wasn't definitively clear to researchers why some babies slept long stretches and others didn't, the researchers did find that babies who were breastfed were more likely to wake up at least once during the night. "This association was present at six and 12 months of age as measured by both the 6-and 8-hour criteria. It's not clear why and more research is needed," the authors wrote, noting that breastfeeding offers many benefits for babies and mothers.
Sleeping through the night between the ages of 6 and 12 months is widely regarded as an important developmental milestone, but Pennestri says not all infants conform to this classic developmental timeline. While increasing percentages of infants sleep through the night as they grow, they also show major interindividual differences.
"Our findings suggest parents might benefit from more education about the normal development of—and wide variability in—infants' sleep-wake cycles instead of only focusing on methods and interventions, especially for those who feel stressed about methods such as delayed response to crying," she says.
Every baby is an individual after all, and whether they sleep through the night at 4 months or 14 months, they all eventually develop and reach milestones in their own time.