Measurement and Determinants of Anogenital Distance in Healthy, Newborn Infants

Abstract

ISEE-0808 Background: In toxicological animal studies, anogenital distance (AGD) is a sexually dimorphic trait that is a well established reproductive toxicity endpoint. AGD develops under the influence of dihydrotestosterone during fetal development, yielding a longer AGD in males when compared to females. A shortened AGD is associated with a variety of genital abnormalities in animal studies of male offspring, but little data exists on the determinants and normal variance of the measurement in humans. Methods: We conducted a standardized training to learn AGD measurement methodologies in the University of Washington newborn nursery in 2008. Inter-rater and intra-rater reliability of measurements, was evaluated prior to the start of the study. We measured 173 (86 male, 87 female) newborn infants for AGD. Standard anthropometric data was collected (weight, length, and occipital head circumference) along with race and gestational complications. We examined AGD for sexual dimorphism and predictors of the measurement in infants using linear regression modeling. Results: Within the standardized training, intra-rater reliability was 0.96 for females and 0.98 for males, and inter-rater reliability was 0.56 for females and 0.92 for males. Mean male AGD was 51.98 mm (SD ± 5.53) and mean female AGD was 37.19 mm (SD ± 3.73). Weight, length, occipital head circumference, and gestational age were independent, significant predictors of AGD. Race was not a strong predictor of AGD. Conclusion: We found that AGD is an easily learned and performed measurement in newborn infants. We demonstrated that AGD is a sexually dimorphic measurement in humans that is most strongly predicted by weight. The application of this measurement to clinically relevant outcomes related to in utero androgenization remains to be explored in further depth.