title: First trimester fetal heart rate as a predictor of newborn sex.
abstract: OBJECTIVE
  To predict the sex of newborns using first trimester fetal heart rate (FHR).
  
  
  METHODS
  This was a retrospective review of medical records and ultrasounds performed between 8 and 13 weeks of gestation. Continuous variables were compared using Student's t-tests while categorical variables were compared using Chi-square test.
  
  
  RESULTS
  We found no significant differences between 332 (50.7%) female and 323 (49.3%) male FHRs during the first trimester. The mean FHR for female fetuses was 167.0 ± 9.1 bpm and for male fetuses 167.3 ± 10.1 bpm (p = 0.62). There was no significant difference in crown rump length between female and male fetuses (4.01 ± 1.7 versus 3.98 ± 1.7 cm; p = 0.78) or in gestational age at birth (38.01 ± 2.1 versus 38.08 ± 2.1 weeks; p = 0.67). The males were significantly heavier than females (3305.3 ± 568.3 versus 3127.5 ± 579.8 g; p < 0.0001) but there were no differences in the proportion of small for gestational age (SGA), average for gestational age (AGA) and large for gestational age (LGA) infants.
  
  
  CONCLUSIONS
  We found no significant difference between the female and male FHR during the first trimester in contrast to the prevailing lay view of females having a faster FHR. The only statistically significant difference was that males weighed more than female newborns.
authors.affiliation: a Department of Obstetrics and Gynecology , West Virginia University, Charleston Campus , Charleston , WV , USA .
authors.forename: L A
authors.initials: LA
authors.lastname: Bracero
authors.affiliation: b Center for Health Services & Outcomes Research, Charleston Area Medical Center Health Education and Research Institute , Charleston , WV , USA , and.
authors.forename: D J
authors.initials: DJ
authors.lastname: Seybold
authors.affiliation: b Center for Health Services & Outcomes Research, Charleston Area Medical Center Health Education and Research Institute , Charleston , WV , USA , and.
authors.forename: S
authors.initials: S
authors.lastname: Witsberger
authors.affiliation: b Center for Health Services & Outcomes Research, Charleston Area Medical Center Health Education and Research Institute , Charleston , WV , USA , and.
authors.forename: L
authors.initials: L
authors.lastname: Rincon
authors.affiliation: b Center for Health Services & Outcomes Research, Charleston Area Medical Center Health Education and Research Institute , Charleston , WV , USA , and.
authors.forename: A
authors.initials: A
authors.lastname: Modak
authors.affiliation: c Department of Obstetrics and Gynecology , New York University Langone Medical Center and School of Medicine , New York , NY , USA.
authors.forename: L V
authors.initials: LV
authors.lastname: Baxi
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D018568:Crown-Rump Length; D005260:Female; D005865:Gestational Age; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000502:physiology; D012189:Retrospective Studies; D012732:Sex Determination Analysis / Q000379:methods*; D016216:Ultrasonography, Prenatal; D055815:Young Adult
keywords: Fetal heart rate; fetal sex; first trimester; newborns; ultrasound