title: Reference intervals of embryos/fetuses heart rate between 6 and 14 weeks of pregnancy.
abstract: OBJECTIVE
  To determine reference intervals for the embryos/fetuses heart rate (HR) between 6 and 14 weeks of pregnancy.
  
  
  METHODS
  A retrospective cross-sectional study was carried in a single center with singleton pregnancies of embryos/fetuses with a crown-rump length (CRL) between 5 and 85 mm. The HR was assessed by real time M-mode or spectrum Doppler ultrasound. To evaluate the correlation between embryo/fetal HR and CRL, polynomial equations were calculated, with adjustment by the determination coefficient (R(2)).
  
  
  RESULTS
  A total of 5867 pregnancies were assessed. The mean gestational age was 10.37 ± 2.12 weeks. The mean maternal age was 26.41 ± 6.78 years. The mean embryo/fetal HR (bpm) for the CRL (mm) intervals 5├15; 15├25; 25├35; 35├45; 45├55; 55├65; 65├75; 75├85 was 145.1 ± 18.7; 167.2 ± 10.1; 166.9 ± 8.7; 165.5 ± 6.9; 162.2 ± 6.8; 159.2 ± 6.4; 157.1 ± 6.4; 154.9 ± 7.3; respectively. The following third-order equation best represented the correlation between embryo/fetal HR and CRL: HR = 119.25 + 3.596*CRL-0.07954*CRL(2 )+ 0.00051*CRL(3) (R(2 )= 0.36).
  
  
  CONCLUSIONS
  Reference intervals of HR in embryos/fetuses in a large sample were determined. These reference intervals can be used in high-risk early pregnancy losses.
authors.affiliation: Referral Center for Teaching of Diagnostic Imaging (CETRUS) , São Paulo - SP , Brazil .
authors.forename: Edward
authors.initials: E
authors.lastname: Araujo Júnior
authors.forename: Raquel Silva
authors.initials: RS
authors.lastname: Costa
authors.forename: Bruna Custódio
authors.initials: BC
authors.lastname: Fonseca
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
authors.forename: Claudio Rodrigues
authors.initials: CR
authors.lastname: Pires
authors.forename: Sebastião Marques
authors.initials: SM
authors.lastname: Zanforlin Filho
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006340:Heart Rate, Fetal; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012016:Reference Values; D012189:Retrospective Studies; D055815:Young Adult
keywords: Embryo; M-mode; fetus; heart rate; reference intervals