BACKGROUND/OBJECTIVE: To study the concentrations of preadipocyte factor-1 (Pref-1) -an inhibitor of adipocyte differentiation, implicated in adipose tissue metabolism, late metabolic disorders and fetal growth- in maternal and umbilical cord serum, as well as maternal milk and correlate above concentrations with intrauterine growth and other perinatal parameters. MATERIAL AND METHODS: Pref-1 concentrations were determined by ELISA in antepartum maternal and umbilical cord serum, as well as day 3 to 4 postpartum breast milk, deriving from 80 women, who delivered 40 appropriate (AGA), 20 large for gestational age (LGA) and 20 intrauterine growth restricted (IUGR) neonates, classified by the use of customized birth-weight standards adjusted for significant determinants of fetal growth. RESULTS: Umbilical cord serum Pref-1 concentrations were significantly higher than antepartum maternal ones (p < 0.001), while breast milk concentrations were the lowest (p < 0.001 concerning umbilical serum, p < 0.001 concerning maternal serum). Umbilical cord serum Pref-1 concentrations were significantly lower in the LGA group than in the AGA one (p = 0.044). Breast milk and maternal serum Pref-1 concentrations did not differ between the three intrauterine growth groups. Maternal serum and breast milk Pref-1 concentrations did not correlate with maternal age, body mass index before and after gestation, birth weight, body length, and customized centile. A positive weak correlation was recorded between maternal serum and milk Pref-1 concentrations (r = 0.238, p = 0.034). CONCLUSIONS: Pref-1 concentrations in umbilical cord serum are higher than in antepartum maternal serum, probably pointing to its fetal origin and role in intrauterine growth. Breast milk concentrations, being extremely low, and possibly implying infant protection from metabolic disorders, positively correlate with maternal serum ones, conceivably suggesting a transfer of the substance from the circulation to the breast. Umbilical cord serum Pref-1 concentrations were lower in LGA fetuses/neonates, as compared to respective AGA ones.