title: Circadian rhythm of frequency-domain measures of heart rate variability in pregnancy.
abstract: OBJECTIVE
  To examine frequency domain measures of heart rate variability and their circadian rhythms in pregnancy.
  
  
  METHODS
  A longitudinal study.
  
  
  METHODS
  University hospital in Turku, Finland.
  
  
  METHODS
  Sixteen healthy women between 11 and 27 weeks of pregnancy; 12 women before pregnancy; and four women postpartum.
  
  
  METHODS
  Heart rate variability as measured in frequency domain from 24-hour ambulatory electrocardiography.
  
  
  RESULTS
  Pregnancy was associated with a lower standard deviation of R-R intervals (P < 0.01), with reduced very low (P < 0.05), low (P < 0.01), and high frequency (P < 0.05) power spectral components of heart rate variability. The high frequency power was lower at night in pregnancy, but similar in the daytime in pregnant and nonpregnant women.
  
  
  CONCLUSIONS
  Pregnancy is associated with an overall reduction in heart rate variability, most markedly reflected in the low frequency component. This suggests altered baroreflex or sympathetic modulation of heart rate, and decreased vagal activation at night.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Turku, Finland.
authors.forename: E M
authors.initials: EM
authors.lastname: Ekholm
authors.forename: J
authors.initials: J
authors.lastname: Hartiala
authors.forename: H V
authors.initials: HV
authors.lastname: Huikuri
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D049590:Postpartum Period / Q000502:physiology; D011247:Pregnancy / Q000502:physiology*