In fact, waking up in the middle of the night is the most common concern that parents of infants report to pediatricians. Now, a new study from Temple psychology professor Marsha Weinraub gives parents some scientific facts to help with that decision.

The study, published in Developmental Psychology, supports the idea that a majority of infants (over 6 months old) are best left to self-soothe and fall back to sleep on their own.

"By six months of age, most babies sleep through the night, awakening their mothers only about once per week. However, not all children follow this pattern of development," said Weinraub, an expert on child development and parent-child relationships.

For the study, Weinraub and her colleagues measured patterns of nighttime sleep awakenings in infants ages six to 36 months. Her findings revealed two groups: sleepers and transitional sleepers.

"If you measure them while they are sleeping, all babies -- like all adults -- move through a sleep cycle every 1 1/2 to 2 hours where they wake up and then return to sleep," said Weinraub. "Some of them do cry and call out when they awaken, and that is called 'not sleeping through the night.'"

For the study, Weinraub's team asked parents of more than 1,200 infants to report on their child's awakenings at 6, 15, 24 and 36 months. They found that by six months of age, 66 percent of babies -- the sleepers -- did not awaken, or awoke just once per week, following a flat trajectory as they grew. But a full 33 percent woke up seven nights per week at six months, dropping to two nights by 15 months and to one night per week by 24 months.

Of the babies that awoke, the majority were boys. These transitional sleepers also tended to score higher on an assessment of difficult temperament which identified traits such as irritability and distractibility. And, these babies were more likely to be breastfed. Mothers of these babies were more likely to be depressed and have greater maternal sensitivity.

The findings suggest a couple of things, said Weinraub. One is that genetic or constitutional factors such as those that might be reflected in difficult temperaments appear implicated in early sleep problems. "Families who are seeing sleep problems persist past 18 months should seek advice," Weinraub said.

Another takeaway is that it is important for babies to learn how to fall asleep on their own. "When mothers tune in to these night time awakenings and/or if a baby is in the habit of falling asleep during breastfeeding, then he or she may not be learning to how to self-soothe, something that is critical for regular sleep," she said.

According to Weinraub, the mechanism by which maternal depression is connected to infant awakenings is an area that would benefit from further research. On the one hand, Weinraub said, it's possible that mothers who are depressed at six and 36 months may have been depressed during pregnancy and that this prenatal depression could have affected neural development and sleep awakenings. At the same time, it's important to recognize that sleep deprivation can, of course, exacerbate maternal depression, she said.

"Because the mothers in our study described infants with many awakenings per week as creating problems for themselves and other family members, parents might be encouraged to establish more nuanced and carefully targeted routines to help babies with self-soothing and to seek occasional respite," said Weinraub.

"The best advice is to put infants to bed at a regular time every night, allow them to fall asleep on their own and resist the urge to respond right away to awakenings."