When do babies start sleeping through the night?

- Sleep-deprived new moms and dads can't wait to have their baby sleep through the night. A new study suggests that about half of babies will be sleeping through the night after about two or three months.

"From five months on, and earlier for some families, parents can realistically expect to experience an uninterrupted and substantial period of sleep," lead researcher Dr. Jacqueline Henderson, of the University of Canterbury in New Zealand, told Reuters Health in an email.

However, the researchers note that there will still be an unlucky few who won't get reprieve until after their child's first birthday.

To add to the limited knowledge regarding an infant's ability to maintain uninterrupted sleep, Henderson and her colleagues looked at sleep patterns across the first year of life for 75 healthy, full-term newborns. They based their assessment on three different criteria: sleeping from midnight to 5 a.m., sleeping through an unspecified eight hours of the night, and sleeping from 10 p.m. until 6 a.m.

Parents kept a diary for six days of each month for 12 months, with the accuracy checked by time-lapse video.

The researchers found that the most rapid increase in uninterrupted sleep occurred between one and four months, during which time babies gradually stretched their sustained snooze time by nearly three hours.

At five months of age, half of infants were giving mom and dad what is usually considered a normal night's rest, by sleeping from 10 p.m. until 6 a.m.

Babies reached the less strict milestones earlier. Half of the babies slept from midnight to 5 a.m. by three months of age and 8 hours a night by four months, report the researchers in the journal Pediatrics.

By 12 months, 85 percent of the babies met these two criteria. However, at this point, one out of every four babies still wasn't sleeping the full span from 10 p.m. to 6 a.m.

"Many infants have difficulties in consolidating their sleep and frequently wake during the night, which is a source of distress for the family," Avi Sadeh of Tel Aviv University in Israel, who was not involved in the study, told Reuters Health in an e-mail. "Understanding normal maturation may help in developing interventions and early prevention tools."

Sadeh, a clinical psychologist with expertise in children and families, noted that such sleep-promoting tools could include creating a sleep environment that is quiet, dark and at an appropriate temperature; maintaining consistent routines and sleep schedules; encouraging a baby to fall asleep and resume sleep in their cribs with little help; and gradually increasing intervals between night feedings.

"Parents should be aware that the developmental process by which infants learn to sleep at night with minimal interruptions occurs very rapidly during the first six months," Sadeh added.