Sonographic measurements of IVC and Ao maximum diameters in term neonates suggests a significant positive correlation among gestational age, BSA, and IVC and Ao diameters. The IVC/Ao ratios remain constant over 48 hours after birth in neonates with weight loss up to 8% of BW, and appear to be lower than previously reported ratios for healthy children.

Stress stimuli, including diseases, disturb homeostasis of the body and enhance secretion of various hypothalamus, pituitary and adrenal gland hormones. One of the main hypothalamic hormones secreted in stress conditions is arginine vasopressin (AVP). Vasopressin concentration in the blood reflects the severity of disease and disorders of blood volume. Measurement of vasopressin is difficult and subjected to considerable laboratory error because of the short half-life in serum and its instability in withdrawn blood samples. This hormone and copeptin are peptides produced during the cleavage of a larger precursor polypeptide: pre-provasopressin. Both peptides are formed in equimolar amounts. Copeptin is a more stable peptide, measurement of which can be performed with higher accuracy. This paper presents the importance of copeptin as a marker of stress, with particular emphasis on the neonatal period, analyzing the impact of gestational age and the route of delivery. Its potential application for assessing the degree of hydration in the adaptation period is also discussed.

Copeptin (CTproAVP) is a stable by-product of arginine–vasopressin synthesis and reflects its secretion by the pituitary gland, considered as a potential new marker of dehydration. The objective of the study was to investigate CTproAVP measured after the first 48 h of postnatal life in relation to serum effective osmolality, urine osmolality, and vessels filling according to the following variables: delivery mode, postnatal weight loss, fluids administered intravenously to the mother, and fluids given orally to the neonate. A prospective observational study was conducted with 200 healthy term infants (53% male) enrolled. Serum CTproAVP concentrations were measured using the ELISA kit; haematocrit, urine osmolality, serum effective osmolality were assessed after 48 h of life. Sonographic measurements of inferior vena cava (IVC) and aorta (Ao) were performed and IVC/Ao ratios were calculated. No correlations were found between CTproAVP concentrations and both serum effective osmolality and urine osmolality. There was also no association between CTproAVP concentrations and vessel filling represented by IVC/Ao index at 48 h of life.