Schulte S, Schreiner F, Plamper M, et al. - In order to analyze the long-term impact of birthweight (bw) on steroid metabolism, researchers investigated genetically identical twins with intra-twin bw-differences from birth to adolescence. Sixty-eight monozygotic twin-pairs with a bw-difference of < 1SDS (concordant; n = 41) and ≥ 1SDS (discordant; n = 27) have been recruited. Morning urine samples were collected and analyzed with gas-chromatography–mass-spectrometry at 14.9 yrs (mean age). In the concordant group, no significant differences were detected. Multiple regression analyses of the smaller twins revealed that among almost all parameters evaluated, individual steroid concentrations of the larger co-twin were the strongest influencing factor. The authors observed that bw had a long-lasting effect on steroid metabolism in monozygotic twin-pairs with greater intra-twin bw-differences (≥ 1SDS), with significant differences in DHEAS-metabolites and relative androgen production. Most parameters, however, exhibited significant intra-twin correlations, indicating a consistent interrelationship between prenatal environment, genetic background, and steroid metabolism.