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

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Introduction Anogenital distance (AGD) and penile length (PL) are considered as surrogate biomarkers of fetal androgen action and are 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 in a large group of Italian newborns and to assess any associations with anthropometric parameters. Methods Data were collected at birth in mother-infant dyads 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 in 4 sub-groups according to birth weight (BW): A(2501–3000 g), B(3001–3500 g), C(3501–4000 g), D (>4001 g). Trained staff measured AGD and PL in newborns with an analogical caliper using the TIDES method. Anogenital distances (AGDs) considered were: ano-scrotal (AGD AS ) and ano-penile (AGD AP ) in males, ano-fourchette (AGD AF ) and ano-clitoral (AGD AC )in females. Correlations among AGDs and anthropometric measures were evaluated by Pearson correlation analysis. P<0.05 was significant. Data were expressed as mean± standard deviation. Results Overall, in males AGDs were longer than in females. Considering the 5 subgroups for GA, AGD AP was significantly longer than AGD AC in neonates born at and after 40 weeks(p<0.05) whereas AGD AS was significantly longer than AGD AF in neonates born at and after 39 weeks(p<0.05). AGD AS increased with increasing GA. Considering AGDs according to BW, AGD AP was significantly longer than AGD AC in newborns with a BW between 3001 and 4000 g(p<0.05), whereas AGD AS was significantly longer than AGD AF in newborns with a BW between 2501 g and 4000 g(p<0.05). Mean PL of male newborns (N = 208) was 24.4 ± 6.83 mm and increased with GA. In the correlation analysis a positive significant correlation was found between AGD AS and PL (r=0.576, p<0.001). Conclusion This study provided measurements and reference values for AGD and PL, based also on GA and BW, in a large group of newborns, supplying a valid well-reproducible instrument for clinical practice and the basis for further studies.

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