Premature born baby is defined as every newborn born before the 37th week of gestation or 259 days after the first day of woman's last menstruation. In the 1960's, term premature include dinfants with low birth weight (< 2500g) born around their estimated due date (born after 37 th week of gestation). Bythe 2000's term for low birth weight infants became separate term. Clinically, pregnancy starts from the last womans menstruation, estimated this way it lasts 280 days, or 40 weeks or 10 lunar months. Human prenatal development divides into embryonic and fetal periods. The duration of the embryonic period is 8 weeks, during which time a human embryo and placenta are formed. According to RonanO'Rahilly and Fabiola Muller, an embryonic period can be divided into 23 Carneige stages. At the end of the stage, the fetus weighs only 2.8 grams. Fetal period takes about 30 weeks during which time the body structures begin to fully form and function after the start of process. Successful transition from fetal to neonatal life requires a complex interaction between the following systems: respiratory, cardiovascular immune and thermoregulatory. Due to under developed organ systems, this change is difficult for preterm babies and therefore they are placed into neonatal intensive care also known as NICU. NICU specializes in the care of our smallest and most sensitive patients. Nurses workin neonatology unit is very responsible and seeks team work in order to provide the most appropriate care.