Objective Heart rate (HR) is an important clinical parameter in newborn infants, but normal ranges are poorly defined. Our aim was to establish normal reference ranges and individual variations in HR as obtained by auscultation in healthy term-born infants during the first 24 hours of life.
Design Observational study.
Setting Single hospital in Norway.
Methods HR was assessed by auscultation for 30 s at 2, 4, 8, 16 and 24 hours of age. Auscultation was validated against ECG recordings.
Subjects Healthy term-born infants who were asleep or awake in a quiet resting state.
Main outcome measures Construction of percentile curves for resting HR.
Results The study included 953 infants. The 50th percentile was 126 beats per minute (bpm) at age 2 hours and thereafter 120–122 bpm. The respective 2nd and 98th percentiles were 102 (thereafter 96–100) bpm and 162 (thereafter 150–156) bpm. The mean HR was 5.6 bpm higher when awake than asleep, 4.9 bpm higher when on the mother’s chest than in the cot, 1.6 bpm higher in girls than in boys, and increased by 0.5 bpm per 0.1°C increase in rectal temperature. Mode of delivery, meconium staining, birth weight and maternal smoking during pregnancy were of no significance. For each infant, HR varied considerably during the first 24 hours (intraclass correlation 0.21 (95% CI 0.18 to 0.24), coefficient of variation 9.2%).
Conclusions The HR percentiles allow for a scientifically based use of HR when assessing newborn infants born at term.
Data availability statement
No data are available.
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Contributors LT conceptualised and designed the study, supervised the data collection, carried out the initial analyses, participated in the interpretation of results and the creation of the percentile figure, and drafted the initial manuscript. TM conceptualised and designed the study, participated in the analysis and interpretation of results, and critically reviewed and revised the manuscript. LMD participated in the analysis and presentation of the data, created the percentile figure, and reviewed and revised the manuscript. TH participated in the analysis and presentation of results, and reviewed and revised the manuscript. All authors approved the final manuscript as submitted.
Funding This work was supported by the South-Eastern Norway Regional Health Authority (Helse Sør-Øst RHF, grant number 2012089) and Innlandet Hospital Trust (grant number 150124).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.