Oct. 25, 2010 -- There's light at the end of the sleep-deprived tunnel for parents of newborns. By age 3 months, and sometimes as early as 2 months, most infants are sleeping through the night, according to a new study, although their sleeping hours may not exactly match those of their parents early on.
"Two months was identified as the most likely age for infants to begin sleeping through the night under both the midnight to 5 a.m. criteria (the one criterion traditionally used to describe sleeping through) and an unspecified eight-hour criteria," says researcher Jacqueline Henderson, PhD, a post-doctoral research fellow of psychology at the University of Canterbury in Christchurch, New Zealand.
By age 5 months, more than half of the 75 infants studied were sleeping the same hours as their parents, the researchers found.
The study is published online in the journal Pediatrics.
Typically, infants' sleep becomes more consolidated with age, evolving from short periods of several hours of sleep followed by several hours of wakefulness over the 24-hour day to a more uninterrupted nighttime sleep.
To investigate how the consolidation takes place and when, Henderson and her colleagues tracked 75 typically developing infants for 12 months. Their parents completed sleep diaries for six days each month and those sleep reports were backed up by videos of the infants' sleeping times.
The researchers considered three different criteria for sleeping through the night:
- Midnight to 5 a.m.
- 8 hours of uninterrupted sleep
- 10 p.m. to 6 a.m., the pattern most in line with family sleep times
When Parents Can Expect Relief
For both the midnight to 5 a.m. and the eight-hour criteria, two months was the most likely age for infants to do this, Henderson says.
''Three months was the most likely age for infants to begin sleeping through from 10 p.m. to 6 a.m, a criterion that better reflects typical family sleep requirements," she says.
"By 5 months of age, 73% were sleeping from midnight to 5 a.m., 62% were sleeping for an eight-hour period, and 53% of infants were sleeping from 10 p.m. to 6 a.m.," she says.
"Further, by the end of the first year, 87%, 86%, and 73% of infants had met the criterion, respectively."
The practical applications? "This is a developmental guide for parents of the capability of healthy, typically developing infants for sleeping through the night," Henderson tells WebMD. "Please remember that each child develops at their own rate as reflected in the different and increasing rates of sleeping through over the first year."
"Parents should not be worried if their infant has not begun to sleep through the night at 2 and 3 months," she says, noting that not all did so.
The new research adds some additional data to previous research and conventional wisdom, says Judith Owens, MD, MPH, associate professor of pediatrics at Alpert Medical School at Brown University and director of the pediatric sleep disorders clinic at Hasbro Children's Hospital, Providence, R.I.
Sleep consolidation, she tells WebMD, "is an important developmental 'sleep milestone' occurring in the first four months of life."
"While two months is perhaps a bit earlier than typically predicted for 'sleeping through the night,' the findings in general are in agreement with previous studies," she says.
Common wisdom has it that an infant will begin sleeping through the night at around age 3 months, Owens says. Before that, short periods of sleep, typically three or four hours, interspersed with short periods of wakefulness, two hours or so, are normal. "At around three months we start to see this ability to consolidate sleep."
Using the criteria of 10 p.m. to 6 a.m., she says, is more helpful as it is more practical for most parents.