Neonatology is a branch of pediatrics that studies the issues of physiology and pathology of newborn infants. The neonatal period commences at birth (baby's first breath) and ends 28 complete days after birth. There is also a distinct perinatal period, which extends from 22nd week of gestation to 7th postnatal day. The important definitions of live births and stillbirths are presented in the table 3.1.
• Live birth means the birth of a product of conception with a gestational age of 22 weeks or more, weight 500 grams or more, or if the baby's weight at birth is unknown, with a body length of 25 cm or more, showing one or more of the four signs of life: breathing, heartbeat, voluntary muscular movements, pulsation of the umbilical cord (ICD-10). • Stillbirth means demise prior to complete expulsion or extraction from its mother of a product of conception, regardless of the gestational age.
Table 3.1. Structural components of perinatal and infant mortality, according to the periods of intrauterine development and the 1st year of life
TRANSITORY CONDITIONS OF NEONATES
After birth, the baby's living conditions undergo radical change; he or she instantaneously enters a completely new environment with significantly lower temperature and humidity, many visual, tactile, auditory, vestibular and other stimuli. After birth, the newborn needs to breathe in a different manner and receive nutrition in a different way, which requires a transformation of almost all functional systems of the body, adaptation to new living conditions different from those in the prenatal period.
The borderline (transition, or adaptive) states of neonates are the states and reactions that reflect the process of adaptation to extrauterine living conditions. These conditions are called borderline, since they arise at the border between two periods of life (intrauterine and extrauterine) and, under certain conditions, may acquire pathological features, leading to disease. These conditions do not develop in all children; however, knowing their laboratory equivalents, clinical and paraclinical manifestations is extremely important for the physician. This period lasts from 2.5 to 5.5 weeks.