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Ajay Thankamony,¹ Ken K. Ong,² David B. Dunger,¹ Carlo L. Acerini,¹ and Ieuan A. Hughes¹

¹Department of Paediatrics, University of Cambridge, Cambridge, United Kingdom; ²MRC Epidemiology Unit, Institute of Metabolic Science, Cambridge, United Kingdom

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.

Materials and 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) .

Conclusion: 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.

Key words: anogenital distance, cryptorchidism, endocrine-disrupting chemicals, endocrine disruption, hypospadias. Environ Health Perspect 117:1786–1790 (2009) . doi:10.1289/ehp.0900881 available via http://dx.doi.org/ [Online 13 Jul 2009]

Address correspondence to I.A. Hughes, University Department of Paediatrics, Box 116, Level 8, Addenbrookes Hospital, Hills Rd., Cambridge, CB2 0QQ, UK. Telephone: 01223-336885. Fax: 01223-336996. Email: iah1000@medschl.cam.ac.uk

We are grateful to the Cambridge Baby Growth Study team.

The study was supported by the European Union Framework V Programme, World Cancer Research Fund International, Mothercare Foundation, and Medical Research Council (UK) . We also thank the Wellcome Trust Clinical Research Facility and the National Institute for Health Research–Biomedical Research Centre, Cambridge.

The authors declare they have no competing financial interests.

Received 4 April 2009 ; accepted 13 July 2009.