OR15-07 Minipuberty in boys: do testosterone levels influence somatic and penile growth?

Abstract Disclosure: K.J. Patterson: None. H.B. Chin: None. M.A. Adgent: None. A. Kelly: None. V.A. Stallings: None. S. Patchel: None. W.J. Rogan: None. D.M. Umbach: None. N. Shaw: None. M. Goldberg: None. Background: Boys experience accelerated somatic and reproductive organ growth during minipuberty of infancy, the transient postnatal activation of the hypothalamic-pituitary-gonadal axis that is associated with increased testosterone production. Previous studies have observed positive associations of testosterone levels with linear growth velocity and penile length in infant boys. Most studies reported relatively weak associations; however, many were based on cross-sectional data. In addition, while testosterone is the standard treatment to increase penile length in infant boys with micropenis, this treatment may lead to supra-physiological levels; as such, it may not be relevant to penile growth in healthy infant boys. Thus, whether penile and somatic growth are influenced by testosterone levels that fall within the normal range in infant boys remains unclear. Hypothesis: Higher testosterone levels will be positively correlated with rate of growth in length, weight, and stretched penile length (SPL) during the first 3 months of life in healthy infant boys. Methods: We used data from 129 infant boys in the Infant Feeding and Early Development Study, a prospective cohort of reproductive development in term, singleton infants enrolled during 2010-2013 from the Philadelphia area. We measured serum testosterone (ng/dL) at the 2-week study visit via mass spectrometry. We measured length (cm), weight (kg), and SPL (cm) at the neonatal (0-3 days of age) and 12-week visits. We calculated the average rate of growth per day by subtracting the neonatal measure from the 12-week measure and dividing by the difference in age in days between the two assessments. We assessed associations of testosterone concentrations with rates of penile and somatic growth using Pearson correlation coefficients (r). We further examined the association of testosterone with penile growth rate using linear regression models adjusted for SPL at the neonatal visit, neonatal weight, or rate of weight gain. Results: Most infants were Black (69%) and fed either soy formula (36%) or cow’s milk formula (36%). The mean testosterone at the 2-week visit was 197 ng/dL (SD=103). Mean SPL was 3.6 cm (SD=0.5) at the neonatal visit and increased to 4.4 cm (SD=0.5) at the 12-week visit. Testosterone was not correlated with rate of growth in length (r=-0.05, p=0.56), weight (r=-0.07, p=0.44), or SPL (r=0.06, p=0.51). Results for penile growth were also null in adjusted models. Conclusions: In this longitudinal cohort of healthy infant boys, testosterone was not associated with somatic growth or growth of the penis. These data may indicate that the testosterone level per se is not critical for normal growth as long as a critical threshold is exceeded. Other factors such as genetics, environment, and androgen receptor activity may have a greater influence on somatic and/or reproductive growth during infancy and deserve further study. Presentation: Sunday, July 13, 2025