title: Anogenital distance from birth to 2 years: a population study.
abstract: BACKGROUND
  Anogenital distance (AGD) is sexually dimorphic in rodents and humans, being 2- to 2.5-fold greater in males. It is a reliable marker of androgen and antiandrogen effects in rodent reproductive toxicologic studies. Data on AGD in humans are sparse, with no longitudinal data collected during infancy.
  
  
  OBJECTIVE
  This study was designed to determine AGD from birth to 2 years in males and females and relate this to other anthropometric measures.
  
  
  METHODS
  Infants were recruited from the Cambridge Baby Growth Study. AGD was measured from the center of the anus to the base of the scrotum in males and to the posterior fourchette in females. Measurements were performed at birth and at 3, 12, 18, and 24 months of age.
  
  
  RESULTS
  Data included 2,168 longitudinal AGD measurements from 463 male and 426 female full-term infants (median = 2 measurements per infant). Mean AGD (+/- SD) at birth was 19.8 +/- 6.1 mm in males and 9.1 +/- 2.8 mm in females (p < 0.0001). AGD increased up to 12 months in both sexes and in a sex-dimorphic pattern. AGD was positively correlated with penile length at birth (r = 0.18, p = 0.003) and the increase in AGD from birth to 3 months was correlated with penile growth (r = 0.20, p = 0.001).
  
  
  CONCLUSIONS
  We report novel, longitudinal data for AGD during infancy in a large U.K. birth cohort. AGD was sex dimorphic at all ages studied. The availability of normative data provides a means of utilizing this biological marker of androgen action in population studies of the effects of environmental chemicals on genital development.
authors.affiliation: Department of Paediatrics, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Ajay
authors.initials: A
authors.lastname: Thankamony
authors.forename: Ken K
authors.initials: KK
authors.lastname: Ong
authors.forename: David B
authors.initials: DB
authors.lastname: Dunger
authors.forename: Carlo L
authors.initials: CL
authors.lastname: Acerini
authors.forename: Ieuan A
authors.initials: IA
authors.lastname: Hughes
mesh_terms: D001003:Anal Canal / Q000033:anatomy & histology*; D000886:Anthropometry / Q000379:methods; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D005836:Genitalia, Female / Q000033:anatomy & histology*; D005837:Genitalia, Male / Q000033:anatomy & histology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D009929:Organ Size; D010413:Penis / Q000033:anatomy & histology; D011446:Prospective Studies; D012727:Sex Characteristics; D006113:United Kingdom