Analysis of Wrist Temperature for Chronobiological Studies in Newborn Babies

*Corresponding author e-mail: cbueno@icb.usp.br Introduction: Temperature rhythm is known to evolve from an ultradian to a circadian pattern in newborn babies earlier than sleep/wake cycle. However, studies following this evolution are limited by difficulties in collecting temperature data in longitudinal series. Recently, a new method for recording wrist temperature continuously was described in adults, allowing the inference of central temperature rhythm. The aim of this study was to investigate the use of wrist temperature in term and preterm newborns for chronobiological research and its relation to axilar and environmental temperature. Methods: Seventeen newborn infants were studied: 4 term babies in the first week of life and 13 preterm newborns betwwen 34 and 36 weeks of post-conceptional age. All subjects used a skin thermistor, Thermochron, attached to the wrist, continuously for 10 to 14 days, which registered temperature every 10 minutes. Axilar temperature was mesured for 14 babies every 4 hours during the whole study and environmental temperature was recorded with the ibbuton also every 10 minutes, continuously. Babies who were in incubators also had their environmental temperature mesured by the own incubator thermistor every 4 hours. Data of wrist, axilar, environment and incubator temperatures (WT, AT, ET and IT, respectively) were compared through Pearson correlation. These data were also submitted to a Lomb Scargle periodogram and a Cosinor analysis, investigating the presence of circadian rhythmicity. Acrophases of significative circadian rhythm observed for each variable were compared in order to investigate a phase relation. Results: WT and AT had a significative correlation for all babies, except one. WT and ET were correlated while babies were maintained inside incubators, but not for babies out of them. However, incubator temperature measured by the own incubator system doesn’t present a significative correlation with WT or AT. WT presented a significative circadian rhythm for all infants, except one term newborn, while AT had circadian rhythm for about 60% of subjects. Most infants had a WT circadian rhythm different from 24 hours. Incubator temperature measured by our thermistor also exhibited circadian rhythm for most subjects, but WT and ET acrophases were not related. Comparing WT and AT acrophases, we found that AT follow WT acrophase in about 2 hours. Conclusion: WT recorded by skin thermistor is a good alternative for studying temperature rhythm in term and preterm infants and seems to be independent of environmental temperature at least for babies out of incubators. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil