USCOM Parameters in Preterm Infants: Reference Ranges

The goal of this observational study is to learn about the feasibility of hemodynamic measurement by the UltraSonic Cardiac Output Monitor (USCOM) in very preterm or very-low-birth-weight infants. The main questions it aims to answer are: 1) establishing reference ranges for USCOM parameters in this specific population, 2) assessing the effect of patients' characteristics and other possible confounders on USCOM parameters, and 3) evaluating the short-term repeatability of the measurement. Participants will receive USCOM measurements on 3, 7, and 14 postnatal days.