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.

Objective
We present longitudinal measurements of fetal and infant AGD. We evaluate the impact of testosterone and dihydrotestosterone at minipuberty on AGD and penile size.

Methods
We performed secondary analyses of an observational, prospective pregnancy and birth cohort, COPANA (2020-2022), at Copenhagen University Hospital—Rigshospitalet, enrolling 685 healthy, singleton pregnant women, of whom 657 attended third trimester ultrasound and 589 infants completed follow-up. Fetal AGD was measured at third semester ultrasound (gestational week 29-34), and infant AGD, penile width, stretched penile length, and circulating testosterone and dihydrotestosterone (LC-MS/MS) were assessed at the minipuberty clinical examination (approximately 3.5 months postpartum):

Results
AGD was available in 650/657 fetuses (310 boys) and 588/589 infants (287 boys). Boys had longer fetal and infant AGD than girls; fetal AGDas: mean (SD) 21.4 mm (±3.5), fetal AGDaf: 12.8 mm (±2.3), P < .001, infant AGDas: 32.0 mm (±5.6) and infant AGDaf: 15.8 (±3.3), P < .001. Fetal AGD correlated with infant AGD in boys and girls (Spearman r = .275, P < .001 and r = .189, P = .001 respectively), but not with circulating testosterone or dihydrotestosterone at minipuberty. Penile size correlated positively with circulating androgen levels at minipuberty: stretched penile length vs testosterone: r = .235, P < .001.

Conclusion
AGD is sexually dimorphic already in the third trimester. Fetal and infant AGD correlate. 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.