Scientists have identified the best way to calm crying infants and get them to sleep, and it involves carrying them rather than simply holding them.
Japanese researchers have found that crying babies are physiologically affected by being held, carried around, and then laid down, identifying an evidence-based soothing strategy presented in a new paper published in Current Biology.
The strategy involves caregivers holding and walking with the baby for five minutes without abrupt movements, followed by 5-8 minutes of holding while sitting, before laying them down for sleep.
“Many parents suffer from babies’ night-time crying,” says senior author Dr Kumi Kuroda of the RIKEN Center for Brain Science in Japan. “That’s such a big issue, especially for inexperienced parents, that can lead to parental stress and even to infant maltreatment in a small number of cases.”
Kuroda and her team had previously found a “transport response” – where the infants calmed down when carried by their mothers – in both distressed mouse pups and human babies. Through complex biological processes, this response results in reduced crying and lower heart rates which help parents to more efficiently transport their babies.
This time, the researchers wanted to compare the effects of the transport response with other strategies used by parents to calm their infants. They used an electrocardiogram (ECG) machine and video cameras to systematically compare changes in heartrate and behaviour for 21 crying infants (newborn to 7 months old) while under four different conditions: being held by their walking mothers, held by their sitting mothers, lying in a still cot, or lying in a stroller rocked backwards and forwards.
They found that within 30 seconds of being held while their mother was walking, crying babies’ heartrates slowed and they calmed down. A similar effect occurred when placed in a rocking stroller, but not when the mother held the baby while sitting or when the baby was placed in a still cot.
This finding suggests that simply holding a baby alone might be insufficient to sooth crying babies. The effect was even more evident when the holding and walking continued for five minutes, as all the babies stopped crying and half fell asleep.
“Walking for five minutes promoted sleep, but only for crying infants. Surprisingly, this effect was absent when babies were already calm beforehand,” adds Kuroda.
The authors suggest that the walking should be carried out on a “flat and clear passage and at a steady pace, preferably without abrupt stops or turns”.
But when the mothers tried to put their babies down to bed, more than one-third became alert again within 20 seconds. The team found that all babies had a physiological response to being separated from their mothers, but if the infants were asleep for a longer period before being laid down, they were less likely to awaken during the process.
“Even as a mother of four, I was very surprised to see the result. I thought baby awoke during a laydown is related to how they’re put on the bed, such as their posture, or the gentleness of the movement,” Kuroda says. “But our experiment did not support these general assumptions.”
Based on their findings sitting and holding babies for another five to eight minutes before putting them to bed might reduce the likelihood of waking the infant.
While the experiment involved only mothers, Kuroda expects the effects are likely to be similar in any caregiver.
“For many, we intuitively parent and listen to other people’s advice on parenting without testing the methods with rigorous science. But we need science to understand a baby’s behaviours, because they’re much more complex and diverse than we thought,” Kuroda says.
“We are developing a “baby-tech” wearable device with which parents can see the physiological states of their babies on their smartphones in real-time,” concludes Kuroda. “Like science-based fitness training, we can do science-based parenting with these advances, and hopefully help babies to sleep and reduce parental stress caused by excessive infant crying.”
Imma Perfetto is a science journalist at Cosmos. She has a Bachelor of Science with Honours in Science Communication from the University of Adelaide.
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