title: Sex ratio of babies is unchanged after transfer of fast- versus slow-cleaving embryos.
abstract: OBJECTIVE
  A higher proportion of male offspring has been observed after transferring faster-developing embryos in a number of animal species. Therefore, we evaluated the correlation between the sex ratio of delivered babies and the cleavage stage of transferred embryos in a human IVF-ET program.
  
  
  METHODS
  The sex of infants born (n = 104) after transfer of exclusively slower-cleaving < or = 3 cell (n = 41) versus exclusively faster-cleaving > or = 4 cell (n = 63) embryos was compared. Furthermore, all boys and girls resulting from IVF-ET (n = 213) were compared with respect to: the average number of cells in the embryos that were transferred, the embryo with the greatest number of cells in the cohort transferred and the percentage of embryos that were faster cleaving.
  
  
  RESULTS
  Thirty seven percent (15/41) of infants resulting from the transfer of exclusively slower-growing embryos were girls and 38% (24/36) of the infants from the faster-growing embryos were girls (NS). The analysis all 213 babies born after 145 embryo transfer procedures did not suggest any differences in embryo cleavage rates in embryo transfers leading to male versus female infants.
  
  
  CONCLUSIONS
  A greater number of boys born was not observed after transfer of faster-cleaving embryos as has been described in other animal species. The race to be male may not occur until later cleavage divisions or may not occur in the human embryo.
authors.affiliation: Department of Obstetrics and Gynecology, Ottawa Civic Hospital, University of Ottawa, Canada.
authors.forename: E
authors.initials: E
authors.lastname: Ng
authors.forename: P
authors.initials: P
authors.lastname: Claman
authors.forename: M C
authors.initials: MC
authors.lastname: Léveillé
authors.forename: N
authors.initials: N
authors.lastname: Tanphaichitr
authors.forename: K
authors.initials: K
authors.lastname: Compitak
authors.forename: S
authors.initials: S
authors.lastname: Suwajanakorn
authors.forename: G
authors.initials: G
authors.lastname: Wells
mesh_terms: D002455:Cell Division / Q000502:physiology; D004624:Embryo Transfer / Q000379:methods / Q000592:standards*; D004622:Embryo, Mammalian / Q000166:cytology* / Q000502:physiology; D005314:Embryonic and Fetal Development / Q000502:physiology*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods / Q000592:standards*; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D012727:Sex Characteristics; D012744:Sex Ratio