How to get a crying baby to sleep, according to science

It’s a frustration many parents know all too well: You’ve finally lulled your crying baby to sleep, so you put them down in their crib … and the wailing begins again. Science may have a trick for you.

Carrying a crying infant for about five minutes, then sitting for at least another five to eight minutes can calm and lull the baby to sleep long enough to allow a parent to put the child down without waking them, researchers report September 13 in Current Biology.

Some of those same researchers previously showed that carrying a crying baby soothes the child and calms a racing heart rate (SN: 4/18/13). For the new study, the team looked at what it takes to get that crying baby to nod off and stay asleep.

The researchers put heart rate monitors on 21 crying babies, ranging in age from newborns to 7 months old. The team also took videos of the infants, monitoring their moods as their mothers carried them around a room, sat holding them and laid them in a crib. That allowed the team to observe how the babies responded to different environments, whether they were crying, fussy, alert or drowsy, heartbeat by heartbeat.

“We tested the physiology behind these things that tend to be kind of common knowledge, though it’s not really well understood why they work,” says Gianluca Esposito, a developmental psychologist at the University of Trento in Italy.  

The babies’ heart rates slowed and they stopped crying when their mothers picked them up and carried them around for five minutes. Some infants even fell asleep. But the researchers also noticed that the babies tended to respond to the movement of the parent, whether they were in deep sleep or not. For instance, a baby’s heart rate quickened if a parent turned quickly while walking or tried to put the baby down.

Sitting seems to smooth that transition from walking to bed, the team observed. Babies cradled in mom’s lap for at least five minutes tended to settle into a slower heart rate and stayed asleep once they were put in their crib. In contrast, the heart rates of six babies whose moms sat with them for less than five minutes accelerated once they were laid down and they woke up soon after.

There’s a lot of research about the relationship between infants and mothers, “but I had not seen work showing that infants were responding to mothers’ behaviors while infants were sleeping,” says Sarah Berger, a developmental psychologist at the College of Staten Island in New York who was not a part of the study.

Both Berger and Esposito caution this method isn’t a magic wand for all babies. It doesn’t rule out sleepless nights, but still, it’s something that parents can try, Esposito says. And while this study was done with mothers, anyone that an infant is comfortable with can do it. “Especially for very, very young kids … as long as these caregivers are familiar with the kid, it’s going to work,” he says.

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