Heart rate in newborns is associated with age, sex and maternal levothyroxine therapy

Asta Uusitalo, Antti Tikkakoski, Pieta Lehtinen, Kaisa Ylänen, Tuija Poutanen, Päivi H. Korhonen

Research output: Contribution to journalArticleScientificpeer-review


Aim: To evaluate the definition and causes of neonatal bradycardias. Methods: This retrospective study included 135 term-born newborns referred for 24-hour Holter monitoring due to bradycardia. Bradycardia was defined as either a heart rate below 80 beats per minute (standard definition) or a heart rate below our recently published age-specific reference values for neonatal heart rate. Results: The mean (SD) age was 6.1 (1.3) days. With standard definition, 107 newborns (79%) had bradycardia, whereas only 20 (15%) had a minimum heart rate lower than the age-specific reference. Younger newborns had lower heart rates. Each day increased the minimum, mean and maximum heart rate by 1.8 (95% CI: 1.0, 2.6), 4.2 (95% CI: 3.0, 5.3) and 2.1 beats per minute (95% CI: 0.3, 3.8), respectively. Male sex and maternal levothyroxine medication were negatively associated with the mean and maximum heart rate. None of the newborns had a cardiac cause for low heart rate. Conclusion: Among term newborns with bradycardias, younger age, male sex and maternal levothyroxine medication were associated with a lower heart rate on Holter monitoring. Given the age-related increase in heart rate, the 80 beats per minute limit as a universal threshold for abnormal heart rate in newborns appears inappropriate.

Original languageEnglish
Pages (from-to)973-979
Number of pages7
JournalActa Paediatrica, International Journal of Paediatrics
Issue number5
Publication statusPublished - 2024
Publication typeA1 Journal article-refereed


  • bradycardia
  • Holter
  • neonatal

Publication forum classification

  • Publication forum level 1

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)
  • Pharmacology (medical)


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