Abstract(#br)Background : Brain-derived neurotrophic factor (BDNF) is abundant in brain and peripheral nerves, affects normal development, growth and survival and is implicated in immune response. Aim : To determine in single preterm (P) and fullterm (F) neonates, circulating intra- and extrauterine levels of BDNF, supposingly reflecting their neuronal and immune maturity. Study design : Prospective study. Subjects : Thirty healthy, appropriate for gestational age (AGA) F (mean gestational age 39.2±1.4 weeks), 15 healthy AGA P (29.4±1.3 weeks), and their mothers. Outcome measures : BDNF was measured by enzyme immunoassay methods in the serum of: mothers at the first stage of labor (MS), the umbilical cord (UC) and the neonates on days 1 (N1) and 4 (N4) postpartum. Results : Levels of BDNF... in (a) FMS did not differ from PMS, but both were significantly higher than respective (F or P) UC, N1 and N4 ( p ranging from <0.01 to <0.001), (b) FUC, FN1 and FN4 were significantly higher than PUC ( p <0.001), PN1 ( p <0.03) and PN4 ( p <0.02), respectively, (c) PN1 increased significantly as compared to PUC ( p <0.05). Conclusions : Higher BDNF MS levels may reflect the mature nervous and immune systems of mothers. Higher BDNF levels in F than P may also be due to advanced maturity in the former. Increased BDNF levels in PN1 as compared to PUC may indicate stimulation of immune response with exposure to antigenic stimuli from the extrauterine environment. Nevertheless, this stimulation is insufficient in P, who by decreasing N4 levels are by far less protected than F.