title: Sex difference in crown-rump length in first-trimester twins.
abstract: OBJECTIVE
  To determine if there is a difference in the crown-rump length (CRL) between male and female fetuses in the first trimester.
  
  
  METHODS
  CRL was determined in 77 normal twin pairs at the time of chorionic villus sampling. The sex of each fetus was assigned based upon the results of the sampling.
  
  
  RESULTS
  A small difference was found between the CRL of males as compared to females, but this was not statistically significant. However, if there was a difference in size between the twin pairs, the odds were 1.5:1 that the larger would be male.
  
  
  CONCLUSIONS
  There is no clinically significant difference in size between male and female fetuses in the first trimester of pregnancy.
authors.affiliation: Department of Obstetrics and Gynecology, Northwestern Memorial Hospital, Chicago, Illinois, USA.
authors.forename: N A
authors.initials: NA
authors.lastname: Ginsberg
authors.forename: A
authors.initials: A
authors.lastname: Cadkin
authors.forename: C
authors.initials: C
authors.lastname: Strom
mesh_terms: D018568:Crown-Rump Length; D005314:Embryonic and Fetal Development; D005260:Female; D006801:Humans; D008297:Male; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012737:Sex Factors; D014427:Twins