External genital features and normative values for anogenital distances and penile length at birth in a healthy Italian population: data from the LIFE-MILCH Project

Introduction: Anogenital distance(AGD) and penile length (PL) have been considered as surrogate biomarkers of foetal androgen action and have been used to study the impact of prenatal exposure to Endocrine Disrupting Chemicals. Data for newborn sex-specific references of both AGD and PL are currently scarce for the Italian population. This study aimed to provide normative data for both sexes in a large group of Italian newborns and to assess any associations with anthropometric parameters. Methods: Data were collected at birth in mothers and their newborns from April 2021 to September 2022.Four hundred and sixty-two/675 neonates at term of uncomplicated pregnancies were enrolled from three different Italian Hospitals. Newborns were divided in 5 subgroups according to weeks of gestational age(GA):1(37-37+6d w),2(38-38+6d w),3(39-39+6d w),4(40-40+6d w),5(>41w) and in4 subgroups according to birth weight (BW):A(2501-3000g),B(3001-3500g),C(3501-4000g), D(>4001g).Trained staff performed the clinical evaluation of newborns and measured AGD and PL with an analogical caliper using the TIDES method. Short anogenital distances (AGDs) were the ano-scrotal (AGDAS ) in males and ano-fourchette (AGDAF )in females. Long AGDs referred to the ano-penile (AGDAP ) in males and anoclitoral(AGDAC) in females. Correlations among AGDs and anthropometric measures were evaluated by multivariate analysis. P<0.05 was significant. Data were expressed as mean±2 standard deviations. Results: Overall, in males both long and short AGDs were longer than in females. Based on the 5 subgroups for GA,AGDAP was significantly longer than AGDAC in the newborns born at and after 40 weeks(p<0.05) whereas AGDAS was significantly longer than AGDAF at and after 39 weeks(p<0.05). AGDAS increased with increasing GA. Considering AGDs according to BW,AGDAP was significantly longer than AGDAC in newborns with a BW between 3001 and 4000g(p<0.05), whereas AGDAS was significantly longer than AGDAF in newborns with a BW between 2501 g and 4000 g (p<0.05). PL of male newborns (N=208) was 24.4±13.66 mm and increased with GA but not with BW. In the multivariate analysis a positive significant correlation was found between AGDAS and PL at birth (r=0.576, p<0.001) and between AGDAS and GA (r=0.224, p<0.05). Conclusion: this study provided measurements and reference values for AGDs and PL, based also on GA and BW, in a large group of newborns, and a valid well-reproducible instrument for clinical practice and the basis for further studies.