Along with other milestones like rolling over and sitting up, new parents often expect their infant will start sleeping through the night by around 6 months of age. But authors of a study in the December 2018 Pediatrics found that a large percentage of developmentally normal, healthy babies don't reach that milestone by 6 months of age, or even a year old.
For the study, "Uninterrupted Infant Sleep, Development, and Maternal Mood", Canadian researchers analyzed information from the Maternal Adversity, Vulnerability, and Neurodevelopment longitudinal birth cohort study, which recruited participants from obstetric clinics in Montreal, Québec and Hamilton, Ontario. Sleeping through the night was defined as either 6 or 8 hours of sleep without waking up. Sleep measures were available for 388 infants at 6 months old, and 369 infants at a year old. At 6 months of age, according to mothers' reports, 38 percent of typically developing infants were not yet sleeping at least 6 consecutive hours at night; more than half (57 percent) weren't sleeping 8 hours. At 12 months old, 28 percent of infants weren't yet sleeping 6 hours straight at night, and 43 percent weren't staying asleep 8 hours.
Researchers also examined whether infants who woke up at night were more likely to have problems with cognitive, language or motor development; they found no association. They also found no correlation between infants waking up at night and their mothers' postnatal mood. But they did discover that babies who woke up during the night had a significantly higher rate of breastfeeding, which offers many benefits for babies and mothers.
Study authors said that sleeping through the night at ages 6 to 12 months is generally considered the "gold standard" in Western nations, where behavioral sleep training is popular among parents and professionals. They said their 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.
Additional Information from HealthyChildren.org: