Rock-a-bye baby: science to the rescue
Crying is just something that babies do. While picking up an infant is often enough to calm them; sometimes they just keep crying and crying.
In 2013, we found that mammal infants become quiet and docile when they are carried by their parents. It is often an emergency that forces animal parents to carry their infants. Thus, the infants cooperate with their parents by withholding their cries and movements. However, we found that infants resumed crying soon after the short bout of carrying. It was also unclear whether the carrying was more effective than other actions.
Soothing a crying baby is a big issue for parents. Nevertheless, there is a lack of research seriously tackling this important topic and measuring infant behavior and physiology second-by-second. That is a surprise.
Transport calms infants
In the current study, we tested the effects of four different maternal behaviors on crying infants: carrying the infant while walking, holding it while seated, placing it in a cot, and moving it in a mobile cot.
Crying decreased when infants were transported, either by carrying or on a mobile cot, but not when they were held.
(Examples of Infant Status Scores and actual infant's status)
5-min transport promotes sleep for crying infants
Next we looked at the effects of carrying infants for 5 minutes.
After 5 minutes of being carried, 46% of infants were asleep and an additional 18% fell asleep within one minute from the end of the walk.
Thus, walking with a crying infant not only soothes its cries but also helps it fall asleep.
(Note: not for quietly alert infants)
Laying the infant down is key
But getting the baby to sleep is not the end of the story. About one third of sleeping infants woke up as soon as they were placed in their bed.
Heart rate reflects the infant’s state
To examine the physiological conditions of the infants, we monitored their heart rates using an electrocardiogram. The interbeat interval (IBI) reflects autonomic activity. When babies are asleep, they have a high IBI (=slow heartbeat), and it gets lower (=faster heartbeat) when they are startled or begin to cry.
Infants sense detachment from the mother
These measurements showed that the infants are alerted most significantly when they are detached from the mother’s body, not when their back touches the bed.
Infants sleep better in a bed than in arms
It was also found that if the infants stayed asleep after being laid down, their IBIs became higher (= heartbeats became slower) than while they were being carried. This means that sleeping babies can rest better in a bed than in their parent’s arms.
Among many factors tested, the sleep duration before the laydown is the key
Here is a dilemma however: placing the sleeping babies down in the bed may wake them up. So what can parents do?
The speed at which they were laid down or the order in which their body parts landed on the bed didn’t affect the success of putting them to sleep. We found that the duration of the infant’s sleep before being laid down was about 8 minutes in successful cases and about 3 minutes in unsuccessful ones.
This finding is consistent with sleep research that shows that an infant’s initial shallow sleep stabilizes after several minutes.
5-minute carrying, 5 to 8 minute sitting for bed
Taken together, the present study proposes a method for soothing a crying baby: carrying it for 5 minutes, then siting down and waiting for another 5 to 8 minutes to facilitate its sleep.
Extending this line of research could shed new light on the complex physiology of infants and could help support parents and caregivers through science-based parenting practices. The method we suggest is cost-free and within the range of normal parenting, so that parents can try it anytime.
When you try this 5-minute carrying methodIf you try "5-minute carrying for a crying baby" at home, please note the following.
- Walk in a clear, flat indoor environment.
- Attach the baby's body snugly to the own body and support the baby’s head. A baby sling or carrier may help if you are used to using them.
- Keep a steady pace of walking, as you walk with a purpose.
- Do NOT run or hop.
- If the baby still cries after 5-10 minutes of carrying, stop walking and check the baby's wellness.
RIKEN AND OUR LAB DO NOT GUARANTEE THE USEFULNESS, CERTAINTY, SAFETY, OR ANY OTHER ASPECT OF THE UTILIZING THE RESULTS OF THIS RESEARCH. REGARDLESS OF THE REASON, WE WILL NOT BE RESPONSIBLE FOR ANY DAMAGE ARISING FROM THE UTILIZING THE RESULTS OF THIS RESEARCH.
Future ExpectationsWe are now working to develop a “baby-tech” wearable device that can provide feedback on the infant’s physiological state in a real-time manner, to reduce parental stress from infant crying and sleep problems.
We are looking for company that can co-develop the product together with us.
Japanese Patent Application No. 2022-035010