title: Sex differences in linear and complex fetal heart rate dynamics of normal and acidemic fetuses in the minutes preceding delivery.
abstract: OBJECTIVE
  To assess linear and complex heart rate dynamics in relation to fetal gender in normal and acidemic fetuses during the minutes preceding delivery.
  
  
  METHODS
  Linear and non-linear fetal heart rate indices, namely mean FHR, long-term irregularity index, short-term variability, low and high frequency spectral indices, approximate and sample entropy, were assessed in 36 female and 30 male fetuses, adjusted for gestational age and weight, during the minutes preceding delivery. Analysis was performed in the initial and final minutes of each tracing in fetuses with umbilical artery blood pH at delivery >or=7.20, 7.11-7.19 and <or=7.10.
  
  
  RESULTS
  Progression of labor was associated with a significant decrease in non-linear indices and an increase in almost all linear indices, both in female and male fetuses, but changes were more marked in female fetuses. Non-acidemic females showed higher mean FHR in the final minutes of labor, compared with males. Acidemic females had higher linear indices when compared to similar male fetuses.
  
  
  CONCLUSIONS
  During the minutes preceding delivery, female fetuses express higher linear indices than male fetuses, suggesting greater activation of the autonomic nervous system, while maintaining similar complexity indices, which suggests different reaction and adaptation capabilities to stress and distress.
authors.affiliation: Departamento de Ginecologia e Obstetrícia, Faculdade de Medicina da Universidade do Porto, Hospital de S. João, Porto and Instituto Nacional de Engenharia Biomédica (INEB), Porto, Portugal. jbernardes59@gmail.com
authors.forename: João
authors.initials: J
authors.lastname: Bernardes
authors.forename: Hernâni
authors.initials: H
authors.lastname: Gonçalves
authors.forename: Diogo
authors.initials: D
authors.lastname: Ayres-de-Campos
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Rocha
mesh_terms: D001724:Birth Weight; D003430:Cross-Sectional Studies; D036861:Delivery, Obstetric; D005260:Female; D005865:Gestational Age; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007743:Labor, Obstetric; D008297:Male; D011247:Pregnancy; D012189:Retrospective Studies; D012727:Sex Characteristics; D014469:Umbilical Arteries