A Method to Calm and Promote Sleep in Crying Babies

Summary

Approximately 20% to 30% of babies cry excessively and have difficulty sleeping for no apparent reason, which causes stress for parents and even triggers impulsive child abuse in a small number of cases. While various sleep training methods or parent education programs may provide long-term improvement of infant crying and sleep problems, there is still no conclusive recommendation for behavioral interventions in place. Previously, we reported that brief infant transport transiently reduces infant crying through the transport response , a coordinated set of vagal activation and behavioral calm conserved in altricial mammals.

In this study, we unravel complex infant responses to maternal carrying and carrying by combining physiological analyzes locked by sub-second-scale events with dynamic mother-infant interactions . Infant crying was attenuated either by maternal movement or by the reciprocal movement provided by a mobile crib, but not by maternal holding alone . Five-minute holding promoted sleep for crying babies even during the day, when these babies were usually awake, but not for non-crying babies. Maternal placement of sleeping infants in a crib exerted bimodal effects , either disrupting or deepening infants’ sleep.

During the act of putting them to bed, sleeping infants were more consistently alerted by the onset of maternal detachment , then calmed after completing maternal detachment in a successful laydown . Finally, sleep outcome after bedtime was associated with sleep duration before bedtime onset. These data propose a scheme of “5 minutes of carrying, 5 to 8 minutes sitting” to address baby crying and sleeping difficulties, which should be corroborated in future studies.

Results and discussion

This study employed four conditions ( Figure 1 A): (1) WalkHold , mother held the infant and walked ( Figure 1 B); (2) SitHold , the mother held the baby and sat down; (3) CRADLE , the infant was placed in a crib; and (4) MCOT , the infant was placed in a mobile crib or stroller and moved manually in a reciprocal motion. The MCOT was conducted only when participants made these devices available. This experimental design segregates the effects of maternal restraint and movement (Figure 1 A), the two sensory components involved in the induction of the transport response. Each task lasted 30 s (short conditions) or 5 min (long conditions) and were randomly alternated within a session (Figure 1 C). Mothers were informed that they could skip a condition when they felt tired or uncomfortable letting their baby cry.

Experimental design (A) The four maternal tasks: WalkHold, SitHold, COT and MCOT. See text for explanation. (B) A typical room layout. Mothers walked back and forth (top) or in circles (bottom) as indicated by the orange line. m, mother; I, infant; e, experimenter. (C) An example of the experiment with a 2-month-old baby and her mother. Top panel: time courses of infant negative vocalization (vowel), eye state, infant state score (ISS), and infant IBI with maternal task transition. Each maternal task was divided by shading color: orange, WalkHold; green, SitHold; light blue, COT; purple, MCOT. Bottom panel: 30 s clustering scheme for the following analysis. Conditions were divided into 30-s intervals and analyzed in pairs with “pre” referring to the last 30-s interval of the previous condition. (D) Elbow analysis. The percentage of variation in mISS values ​​for all 30 s intervals analyzed, as explained by the number of groups. The percentage of variance is the ratio between the variance between groups and the total variance. The orange line delimits the point on the graph (3 clusters) at which a further increase in the number of clusters does not produce a significant change in the percentage of explained variance. (E) Histogram plotting the distribution of ISS values ​​for all 30 s bins. The dashed lines represent the borders of the three groups determined in (D). The “alert” group was divided into three groups based on whether the ISS was greater than, equal to, or less than 0. See also Video S1. (F) The distribution of mISS and mIBI overall. mIBI was correlated with mISS using Spearman’s rank correlation test (ρ = 0.75, p < 0.001).

The present study is exploratory and needs confirmation in more specific experiments with larger samples. To retain naturalistic mother-infant behaviors, we allowed flexibility in task duration and did not strictly control vocal or nonverbal communications with the mother, which are known to affect infants’ emotional state.

Other parameters that can affect the results are movement speed, frequency, time of the experiment (at night or during nap), babies’ crying habits, and sleep routines. Furthermore, the effects of transportation should be compared between mothers and non-maternal caregivers because movement-based baby calming is commonly performed by fathers, grandparents, and child care professionals in several countries, including Japan.

Nevertheless, this study provides proof of concept that infant carrying significantly reduces crying and potentially promotes sleep, and proposes a behavioral protocol, "hold 5 minutes, sit before bed 5 to 8 minutes" for infants who they cry To hold the baby safely, caregivers should hold the baby’s body comfortably to their own body and support the baby’s head. The five-minute walk should be on a flat, clear path and at a constant pace, preferably without sudden stops or turns. With these precautions, this protocol can be performed safely within the range of regular parental attention.

It should be noted that unlike most behavioral interventions for childhood sleep difficulties, this protocol does not address any long-term improvements in sleep regulation. Instead, this protocol provides immediate relief from baby crying and may be especially helpful on special occasions when regular sleep routines, breastfeeding, or pacifiers are ineffective or unavailable.