A crying baby in the middle of the night is one of those sobering facts of parenthood, but parents might actually not need to rush to the crib if there’s a wail from the nursery. A new psychology study suggests most babies can be left alone to fall back asleep.

In a study published in the journal Developmental Psychology, Temple University psychologist Marsha Weinraub and her colleagues followed more than 1,200 infants throughout the first three years of their life. The child’s parents reported how often the baby woke up in the middle of the night.

The team found that by the time the babies reached six months, most of them woke their parents in the middle of the night no more than once or twice a week. Other patterns emerged as well.

“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," Weinraub said in a statement on Wednesday. “Some of them do cry and call out when they awaken, and that is called 'not sleeping through the night.'”

The babies who cried more when they woke were more likely to be boys and to have difficult tempers. Breast-feeding may also be a factor in infant sleep disturbances, as babies who become accustomed to falling asleep while nursing may find it more difficult to go back to sleep on their own than bottle-fed babies.

“Early in infancy, breast-fed babies may awaken more frequently throughout the night than formula-fed infants because breast milk is digested more quickly; later in infancy, breast-fed infants may awaken more frequently, not because they are hungry but because they have difficulty returning to sleep without the customary nursing,” Weinraub and her colleagues wrote.

Maternal depression was another common factor among the babies who regularly woke their parents up, but the authors noted that this connection needs further study. While depression during pregnancy may have influenced a baby’s development and led to sleep disruptions, the connection could go the other way -- depression could be aggravated by a mother’s sleepless nights.

Overall, Weinraub and her colleagues recommend a course of action that parents might find appealing: ignore the crying baby. By immediately rushing to calm a temperamental infant, the parents might be further weakening his or her ability to fall back asleep unaided.

Persistant sleep problems that last for more than 18 months may be a sign that parents need to talk to a pediatrician.

But in general, "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,” Weinraub says.

SOURCE: Weinraub et al. “Patterns of Developmental Change in Infants’ Nighttime Sleep Awakenings from 6 through 36 Months of Age.” Developmental Psychology 48: 1511-1528, 2012.