title: 2nd to 4th digit ratios, fetal testosterone and estradiol.
abstract: BACKGROUND
  The ratio of 2nd to 4th digit length (2D:4D) is sexually dimorphic (mean 2D:4D is lower in males than females) and is thought to be fixed early in development. 2D:4D has been reported to be related to fetal growth, hand preference, autism, Asperger's syndrome, sperm counts, family size, age at myocardial infarction in men and breast cancer in women. There is indirect evidence that 2D:4D is established in utero and is negatively related to prenatal testosterone and positively with prenatal estradiol. However, there are no studies which show direct relationships between fetal testosterone (FT), fetal estradiol (FE) and 2D:4D.
  
  
  OBJECTIVE
  To investigate the relationships between 2D:4D ratios and FT and FE from amniotic fluid.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  33 children.
  
  
  METHODS
  Radioimmunoassays of FT and FE obtained from routine amniocentesis; 2D:4D ratios calculated from 2nd and 4th digit length of the right and left hands at age 2 years.
  
  
  RESULTS
  A significant negative association between right 2D:4D ratio and FT/FE ratio, which was independent of sex.
  
  
  CONCLUSIONS
  These preliminary findings lend support to an association between low 2D:4D and high levels of FT relative to FE, and high 2D:4D with low FT relative to FE.
authors.affiliation: Developmental Psychiatry Section, University of Cambridge, Douglas House, 18b Trumpington Road, Cambridge CB2 2AH, UK.
authors.forename: S
authors.initials: S
authors.lastname: Lutchmaya
authors.forename: S
authors.initials: S
authors.lastname: Baron-Cohen
authors.forename: P
authors.initials: P
authors.lastname: Raggatt
authors.forename: R
authors.initials: R
authors.lastname: Knickmeyer
authors.forename: J T
authors.initials: JT
authors.lastname: Manning
mesh_terms: D000649:Amniocentesis; D000653:Amniotic Fluid / Q000737:chemistry*; D000886:Anthropometry; D015331:Cohort Studies; D004958:Estradiol / Q000032:analysis*; D005260:Female; D005385:Fingers / Q000196:embryology*; D006801:Humans; D016014:Linear Models; D008297:Male; D011247:Pregnancy; D012727:Sex Characteristics; D013739:Testosterone / Q000032:analysis*
chemical_list: D013739:Testosterone; D004958:Estradiol