Sex-specific ranges and ratios for anogenital distance among Thai full-term newborns 

INTRODUCTION: Anogenital distance (AGD) is a marker of prenatal androgen exposure and a tool for assessment of differences of sex development. Data for AGD in newborns have been published, but these findings may not be applicable to Thai newborns. AIM: To provide the sex-specific ranges for AGD in Thai full-term newborns. METHODS: A cross-sectional study was conducted in term newborns in Thailand, during 2016–2018. AGD was measured from anus to anterior base of penis (AGD(AP)) and to perineoscrotal junction (AGD(AS)) in males and from anus to clitoris (AGD(AC)) and to posterior fourchette (AGD(AF)) in females. AGD ratio is defined as AGD(AS) divided by AGD(AP) in males and AGD(AF) divided by AGD(AC) in females. RESULTS: A total of 364 newborns were studied (male 51.4%). The mean AGD(AS), AGD(AP) and AGD ratio in males were 25.20 ± 4.80, 52.60 ± 6.90 and 0.48 ± 0.08 mm, respectively. The mean AGD(AF), AGD(AC), and AGD ratio in females were 16.50 ± 3.90, 42.60 ± 6.20 and 0.39 ± 0.08 mm, respectively. There were significant differences between AGD(AS) and AGD(AF), AGD(AP) and AGD(AC), and AGD ratio between males and females (p < 0.001). The AGD(AS), AGD(AP), AGD(AF), AGD(AC) were correlated with birth weight and length, but AGD ratio showed no correlation. CONCLUSION: The sex-specific ranges for AGD in Thai full-term newborns were determined. AGD ratio is a useful marker of prenatal androgen exposure since it differs between sexes, but constant between races and did not vary by body size.