title: Sex ratio is remarkably constant.
abstract: OBJECTIVE
  To study whether the sex of the offspring is related to increasing parental age, gravidity, and parity, hypothesizing an altered male-to-female sex ratio with the advancing parental age.
  
  
  METHODS
  A large retrospective cohort study.
  
  
  METHODS
  The study analyzed birth records of Hadassah Hebrew University Medical Center in Jerusalem from June 2003 to December 2006.
  
  
  METHODS
  35,837 birth records were analyzed including 941 multifetal deliveries, excluding foreign inhabitants (n = 744), missing data for the main study outcome (n = 2) and parturients over 50 years to control for egg donation (n = 26).
  
  
  METHODS
  None.
  
  
  METHODS
  Male-to-female sex ratio.
  
  
  RESULTS
  The male-to-female sex ratio of all the newborns was 1.05. This ratio did not change significantly with either maternal or paternal age. Neither gravidity nor parity affected the male-to-female ratio. The only factor that affected the regression of sex ratio was the length of gestation.
  
  
  CONCLUSIONS
  Sex ratio at birth is remarkably constant. No association was found between parental age or birth order and neonatal sex ratio.
authors.affiliation: Department of Obstetrics and Gynecology, Hadassah Hebrew University Medical Center, Jerusalem, Israel.
authors.forename: Eliana
authors.initials: E
authors.lastname: Ein-Mor
authors.forename: David
authors.initials: D
authors.lastname: Mankuta
authors.forename: Drorith
authors.initials: D
authors.lastname: Hochner-Celnikier
authors.forename: Arye
authors.initials: A
authors.lastname: Hurwitz
authors.forename: Ronit
authors.initials: R
authors.lastname: Haimov-Kochman
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D005260:Female; D020073:Gravidity; D006801:Humans; D007231:Infant, Newborn; D007557:Israel / Q000453:epidemiology; D050498:Live Birth / Q000453:epidemiology*; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D010298:Parity; D010331:Paternal Age; D011247:Pregnancy; D012016:Reference Values; D012189:Retrospective Studies; D012744:Sex Ratio; D055815:Young Adult