title: Changes in 24-hour heart rate variability during normal pregnancy.
abstract: OBJECTIVE
  We studied the effects of normal pregnancy on heart rate variability as a noninvasive index of maternal cardiovascular autonomic modulation.
  
  
  METHODS
  Twenty-four-hour Holter recordings were obtained for 8 healthy pregnant volunteers during early pregnancy (</=6 weeks after conception); at 10, 18, and 34 weeks after conception; and while the subjects were not pregnant. Another 12 subjects underwent 2 to 4 recordings in the sequence. Heart rate variability and nighttime respiratory rates were determined.
  
  
  RESULTS
  Maternal heart rate variability declined during pregnancy. Virtually all indexes were significantly decreased with respect to the nonpregnant state in early pregnancy, and respiratory rate was increased. Changes in heart rate, heart rate variability, and respiratory rates between subsequent stages were modest. Individual changes in heart rate, heart rate variability, and respiration during pregnancy varied in both magnitude and direction.
  
  
  CONCLUSIONS
  Most of the change in cardiac autonomic modulation and respiration during pregnancy occurs within the first 6 weeks after conception. There is considerable variability in individual heart rate and heart rate variability changes during a normal pregnancy.
authors: Division of Cardiology, Washington University School of Medicine and Barnes-Jewish Hospital, St Louis, Missouri, USA.
authors: P K
authors: PK
authors: Stein
authors: M T
authors: MT
authors: Hagley
authors: P L
authors: PL
authors: Cole
authors: P P
authors: PP
authors: Domitrovich
authors: R E
authors: RE
authors: Kleiger
authors: J N
authors: JN
authors: Rottman
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D011247:Pregnancy / Q000502:physiology*; D012016:Reference Values; D012119:Respiration