Endocrine-Sensitive Physical Endpoints in Newborns: Ranges and Predictors

BACKGROUND: In neonates, endocrine-sensitive physical endpoints, including breast and reproductive tissues may reflect effects of fetal environmental exposure. Studies using standardized measurement techniques that describe demographic and clinical variability in these endpoints are lacking. METHODS: 388 healthy term newborns <3 days old were evaluated, 69% African American and 25% White. Measures included breast bud diameter, anogenital distance (AGD), stretched penile length (SPL), and testicular volume (TV). RESULTS: Breast buds were larger in females than males bilaterally (right: 13.0±4.0 vs. 12.0±4.0 mm, p= 0.008; left: 13.0±4.0 vs. 11.0±3.0 mm, p<0.001). Breast bud size correlated positively with gestational age (Regression coefficient=0.46±0.12 mm, p<0.001) and weight Z-score (0.59±0.24 mm, p=0.02), and negatively with White race (−1.00±0.30 mm, p=0.001). AGD was longer in males (scrotum-to-anus) than females (fourchette-to-anus) (21.0±4.0 vs. 13.0±2.0 mm, p<0.001) and did not differ by race. SPL was shorter in White infants (35.0±5.0 vs. 36.0±5.0 mm, p=0.04). Median TV was 0.5 cm(3), and larger in White males (OR 1.71, 95%CI: 1.02-2.88) CONCLUSIONS: This study provides a range of physical measurements of endocrine-sensitive tissues in healthy infants from the US, and the associations with demographic and clinical characteristics.