It’s every parent’s nightmare: an exhausted baby who won’t stop crying when it’s bedtime. Even worst? The baby finally falls asleep in your arms, but wakes up again and starts sobbing when you lay him down in his crib.
The solution is a pair of magic numbers, five and eight, according to Japanese researchers who experimented with 21 mothers trying to soothe their little ones at bedtime.
Here’s how it works: Walk your baby for at least five minutes without sudden movements, at which point your little one will be calm, if not asleep, according to the study. Then sit and hold the baby for eight minutes, before gently placing him in the crib.
Putting the sleeping baby to bed without first sitting quietly with him for eight minutes ended in disappointment, according to study author Kumi Kuroda, team leader at the affiliated social behavior unit at the Riken Center for Brain Science in Saitama, Japan.
“Although we didn’t predict it, the key parameter for the success of putting sleeping babies in cribs was the (delay) from the onset of sleep,” Kuroda said.
“I raised four children and did these experiments, but even I couldn’t predict the main results of this study until the statistical data came out,” he added.
Timing guidelines may be helpful for some parents and caregivers, but they won’t necessarily work for everyone, said pediatrician Jennifer Shu, medical editor-in-chief of the American Academy of Pediatrics’ parenting website.
“Babies are different and (some) may not respond to this system,” said Shu, who was not involved in the study.
Parents and caregivers should not use this technique regularly if a baby is able to fall asleep on their own, added Shu, who is also the co-author of Heading Home With Your Newborn: From Birth to Reality: from birth to reality, in literal translation).
“The goal should be to ensure that the baby is sleeping well, using this or other techniques, while eventually encouraging him to fall asleep on his own, both at the beginning of bedtime and during the night ( when he wakes up),” Shu said.
Heart beat fundamentals
The study, published in the journal Current Biology, looked at the impact of four calming behaviors on infant crying. Mothers were asked to hold their baby while they were walking, to walk the baby in a stroller or “mobile crib”, to hold the baby while sitting, and finally to put the baby directly in a crib. The researchers monitored the baby’s heartbeat and videotaped each session to record and time the response.
Sitting and holding a crying baby didn’t work, the study found. The monitors showed that the baby’s heart rate rose and the behavior continued. It was no surprise that putting the crying baby directly into the crib didn’t work either.
Only movement calmed the babies, the study found. Within five minutes, all babies held by walking mothers had stopped crying, heart rate had slowed and 46% of babies were asleep. And 18% of babies fell asleep after a few more minutes, the study found.
However, the five-minute walk brought only crying babies to sleep. “Surprisingly, this effect was absent when the babies were already calm,” Kuroda said.
The researchers saw similar results when parents pushed babies in strollers, but the impacts were not as consistent.
Now for the even more difficult part: putting babies to sleep in their cribs without waking them up. A third of the babies in the study woke up immediately after being put in the crib, no matter how soft the parents were. But it wasn’t the touch of the bed on the baby’s body that woke them, the study found. Instead, the monitors showed that the baby’s heartbeat response spiked as soon as it was separated from the mother’s body.
However, when the babies were held for an additional eight minutes, they entered a more stable sleep state, a state that did not waver when they were separated from their mother, the researchers found.
Why does being on your lap work?
Human babies, like other mammals, respond to what’s called the “carriage response,” an innate reaction seen in species with babies too immature at birth to walk or fend for themselves.
We see it in nature videos all the time: mothers of lions, tigers and other wild cats, as well as their domesticated cousins, carry their babies by the neck. As well as wild and domestic dogs, mice and rats. Great apes, monkeys and other primates carry their babies on their backs, where they cuddle and cuddle, just like skunks and giant anteaters. Marsupials such as kangaroos, koalas and wallabies have specialized pouches to cradle their babies as they grow.
The answer seems instantaneous. Once the mother picks up the baby and starts moving, the baby is relatively docile and its heart rate slows down, according to research done by Kuroda and his team.
Unfortunately, it seems that humans aren’t as lucky as other mammalian mothers and have to hold their young longer to get the same response. There’s another thing that sets people apart: the need for human babies to learn to sleep on their own.
“Holding a baby or rocking him until he’s fully asleep creates a routine that the baby will learn to expect,” Shu said. “When your baby wakes up in the middle of the night in a light sleep phase (as we all do), it may require the routine to be repeated.”
For babies four months and older, the American Academy of Pediatrics (AAP) recommends putting them to bed when they are sleepy, rather than waiting for them to fall asleep completely.
And don’t rush to soothe a baby over three months old when he wakes up, the AAP advised. Like adults, your baby can toss and turn and fall asleep again.
Don’t forget to follow the guidelines for safe sleep: babies should always be placed on their back during naps and at night, in an approved crib without padding, pillows, soft stuffed animals, blankets, diapers or blankets.