title: Changes in the frequency power spectrum of fetal heart rate in the course of pregnancy.
abstract: OBJECTIVE
  The aim of this study was to examine changes in the heart rate variability based on the frequency power spectrum of healthy fetuses during the second and third trimester of pregnancy.
  
  
  METHODS
  We analyzed 222 fetal magnetocardiograms recorded in 49 healthy singleton pregnancies between the 16th and 42nd week. Discrete Fourier transformation was performed on the time-based step function of the RR-intervals. Changes of spectral density in the frequency spectrum in various bands between 0.003 to 1 Hz, including low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.40 Hz) bands, were examined as a function of gestational age.
  
  
  RESULTS
  Spectral density between 0.003 to 1.0 Hz increased with gestational age with large changes, in particular, at lower frequencies. At approximately the 32nd week, the rate of increase in power slowed substantially. Prior to this time, the rates of change in power were different for the bands 0.003 to 0.40 Hz, 0.40 to 0.60 Hz and 0.60 to 1.0 Hz. LF and HF showed similar development, with HF increasing slightly more rapidly.
  
  
  CONCLUSIONS
  We conclude that characteristic spectral bands that increase in spectral density at different rates during the second and third trimester may be identified. They most likely reflect developmental changes and behavioral states during pregnancy.
authors.affiliation: Department of Biomagnetism, Research and Development Center for Microtherapy (EFMT) Bochum, Germany. petervl@microtherapy.de
authors.forename: Peter
authors.initials: P
authors.lastname: Van Leeuwen
authors.forename: Daniel
authors.initials: D
authors.lastname: Geue
authors.forename: Silke
authors.initials: S
authors.lastname: Lange
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hatzmann
authors.forename: Dietrich
authors.initials: D
authors.lastname: Grönemeyer
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D005583:Fourier Analysis; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D008280:Magnetics; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011296:Prenatal Diagnosis / Q000379:methods*