MONDAY, Oct. 25 (HealthDay News) -- New research may offer some relief to sleep-starved parents: Most infants will start sleeping through the night between 2 and 4 months of age.

What may take a little longer, however, is for the baby's eight hours of slumber to conform to the family's sleep schedule, according to the study.

"The most rapid changes in infant sleep were found to occur over the first four months of life. Previously, we underestimated infants' capabilities for sleeping through the night, and we found that if an infant is sleeping for the traditional period of night sleep -- five hours from midnight to 5 a.m. -- then they are also sleeping for eight hours. Infants are most likely to begin sleeping through for this period at 2 months of age, with over 50 percent doing so at four months," said study author Jacqueline Henderson, a postdoctoral research fellow at the University of Canterbury in New Zealand.

"Given this, we examined another definition of 'a night's sleep' that better suits family members' sleep requirements, from 10 p.m. to 6 a.m. We found infants are most likely to begin sleeping during this period at age 3 months, with over 50 percent doing so at five months," she said.

Still, many infants -- as their beleaguered parents will attest -- won't meet these milestones, even at 1 year of age.

"By the end of the first year, 87 percent of infants are sleeping for five hours, 86 percent for eight hours and 73 percent of infants from 10 p.m. to 6 a.m.," Henderson noted.

For the study, Henderson and her colleagues recruited parents of 75 full-term infants who agreed to complete sleep diaries for six days each month. The researchers verified the information in the sleep diaries using a video sleep study.

They assessed the infant sleep using one of three criteria: uninterrupted sleep from midnight to 5 a.m., at least eight uninterrupted hours of sleep, or sleeping according to the family schedule -- with uninterrupted sleep between 10 p.m. and 6 a.m.

Results of the study were published online Oct. 25 in the journal Pediatrics.

"I think parents are most interested in the third criterion -- does the baby sleep in sync with the parents?" said Dr. Sangeeta Chakravorty, director of the pediatric sleep evaluation center at Children's Hospital of Pittsburgh.

And, she added, "sometimes, we try too hard to make this happen," and that may lead to disruptive sleep habits. "Understanding infant sleep patterns, knowing what you need, and learning how to match the two is the art and science of parenting. But, the pressures of modern life don't always allow parents and child to develop that balance," she said.

Dr. Hugh Bases, a developmental pediatrician at NYU Langone Medical Center, said it's important to note that this study was done with babies who were born full-term, so the findings don't necessarily apply to preterm infants. In addition, about half the infants were second-born children, so their parents were more experienced.

His advice to parents is to develop good sleep habits early on. That means:

• Put your baby down in the crib when he or she is still awake -- drowsy, but awake.
• Don't rock your baby to sleep, or let your baby fall asleep on you.
• If your baby wakes up in the middle of the night, don't immediately go to him or her. Give the baby some time to settle alone.
• If the baby continues to cry, and you feel that you can't wait any longer, make your visit with your infant as limited and boring as possible. Don't pick the baby up. Instead, comfort the baby -- rub the baby's back, speak in a quiet voice -- and then leave.
• If your baby simply won't be soothed this way, you can always give in for the night and pick the baby up, and then try again the next night.

Bases also noted that once your baby has started sleeping through the night, you should expect that there will still be some nights when your baby wakes up. For example, if your baby isn't feeling well. "Lots of things can disrupt the sleep cycle. Sleeping through the night is often accomplished in fits and starts. The good news is that kids can be easily retrained to sleep through the night again," he said.

More information

For more advice on getting your baby to sleep, visit the American Academy of Pediatrics.