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CONTEXT: The anogenital distance (AGD) is considered a postnatal readout of early fetal androgen action. Little is known of prenatal AGD and how it correlates with AGD postnatally. OBJECTIVES: We present longitudinal measurements of fetal- and infant AGD. We evaluate the impact of testosterone and dihydrotestosterone at minipuberty on AGD and penile size. DESIGN: Secondary analyses of an observational, prospective pregnancy and birth cohort, COPANA (2020-2022). SETTING: Copenhagen University Hospital - Rigshospitalet. PARTICIPANTS: 685 healthy, singleton pregnant women enrolled, 657 women attended 3rd trimester ultrasound, 589 infants completed follow-up. MAIN OUTCOME MEASURES: 3rd trimester ultrasound (GW29-34): Fetal AGD. Minipuberty clinical examination (app. 3.5 months postpartum): infant AGD, penile width and stretched length (SPL), circulating testosterone and dihydrotestosterone (LC-MS/MS). RESULTS: AGD was available in 650/657 fetuses (310 boys) and 588/589 infants (287 boys). Boys had longer fetal and infant AGD compared to girls; fetal AGDas: mean (SD) 21.4 mm (±3.5), fetal AGDaf: 12.8 mm (±2.3), p < 0.001, infant AGDas: 32.0 mm (±5.6) and infant AGDaf: 15.8 (±3.3), p < 0.001. Fetal AGD correlated with infant AGD in boys and girls (Spearman's r = 0.275, p < 0.001 and r = 0.189, p = 0.001 respectively), but not with circulating testosterone or dihydrotestosterone at minipuberty. Penile size correlated positively with circulating androgen levels at minipuberty, i.e.: SPL vs testosterone: r = 0.235, p < 0.001. CONCLUSIONS: AGD is sexual dimorphic already in the 3rd trimester. Fetal and infant AGD correlates. AGD is associated with body size but not circulating androgen levels at minipuberty. These findings suggest that fetal and infant AGD, reflect androgen action during early fetal development.
Fischer et al. (Sat,) studied this question.