Objective: To investigate the effects of delivery route and maternal anesthesia type and the roles of vasoactive hormones on early postnatal weight loss in term newborns. Methods: Ninety-four term infants delivered vaginally (group 1, n=31), cesarean section (C/S) with general anesthesia (GA) (group 2, n=29), and C/S with epidural anesthesia (EA) (group 3, n=34) were included in this study. All infants were weighed at birth and on the second day of life and intravenous (IV) fluid infused to the mothers for the last 6 h prior to delivery was recorded. Serum electrolytes, osmolality, N-terminal proANP (NT-proANP), brain natriuretic peptide (BNP), aldosterone and plasma antidiuretic hormone (ADH) concentrations were measured at cord blood and on the second day of life. Results: Our research showed that postnatal weight loss of infants was higher in C/S than vaginal deliveries (5.7 % vs. 1.3 % ) (p<0.0001) and in EA group than GA group (6.8 % vs. 4.3 % ) (p<0.0001). Postnatal weight losses were correlated with IV fluid volume infused to the mothers for the last 6 h prior to delivery (R=0.814, p=0.000) and with serum NT-proANP (R=0.418, p=0.000), BNP (R=0.454, p=0.000), and ADH (R=0.509, p=0.000) but not with aldosterone concentrations (p>0.05). Conclusion: Large amounts of IV fluid given to the mothers who were applied EA prior to the delivery affect their offsprings' postnatal weight loss via certain vasoactive hormones. © 2011 by Walter de Gruyter Berlin New York.