Neonatology is a subspecialty of pediatrics defined as the care of the ill or premature newborn infant. It is a boarded, hospital-based branch of medicine. Most neonatal medicine is practiced in neonatal intensive care units (NICUs). The principal patients of neonatologists are newborn infants who are ill or requiring special medical care due to prematurity, low birth weight (intrauterine growth retardation, or congenital malformations (birth defects)). Neonatologist is usually a pediatrician, who has completed additional training (for 3 years in US), and is board certified. Pediatrics (also spelled paediatrics or pædiatrics) is the branch of medicine that deals with the medical care of infants, children, and adolescents. ... A physician visiting the sick in a hospital. ... A newborn infant sleeping in his incubator. ... Prematurity is the condition of being born before a full gestation. ... Intrauterine growth retardation or Intrauterine growth restriction (IUGR) refers to the condition during pregnancy where a fetus is considered to be too small for its gestational age (generally in the 10th percentile). ... A congenital disorder is a medical condition that is present at birth. ... A congenital disorder is a medical condition or defect that is present at or before birth (for example, congenital heart disease). ... Pediatrics (also spelled paediatrics or pædiatrics) is the branch of medicine that deals with the medical care of infants and children. ...