The aim of the study is to evaluate urine NT-proBNP levels and new Echocardiographic Findings in VLBW infants. The investigators hypothesize that high urine NT-proBNP concentrations are associated with a hemodynamically significant ductus arteriosus. The investigators also hypothesized that new echocardiographic parameters such as isovolumic relaxation time (IVRT)is useful for the prediction of ductus intervention.

Urine samples were collected within 24 to 48 hours of age, on day 7, on day 14 and on day 28 of life. The samples were spun and the platelet-free urine was stored at -80°C until NT-proBNP analysis. The NT-proBNP assay was performed with an automated immunoassay (Roche Diagnostics). Color Doppler and tissue Doppler echocardiography was determined at the same time as the urine collection. New echo parameters such as IVRT, tissue velocity, strain and strain rate were measured and compared with the standard parameters for significant ductus arteriosus. Furthermore we compared the tissue Doppler measurements with clinical findings.

Inclusion Criteria:

• Written parental informed consent
• VLBW infants
• Admitted to our NICU within 48 hours after birth

Exclusion Criteria:

• No written parental informed consent
• Congenital heart disease
• Death

VLBW infants