Perinatology: A subspecialty of obstetrics concerned with the care of the mother and fetus at higher-than-normal risk for complications. Since the perinatal period, depending on the definition, starts at the 20th to 28th week of gestation and ends 1 to 4 weeks after birth, perinatology logically could be an obstetrical and pediatric subspecialty but, in practice, it is part of obstetrics. The comparable area of pediatrics is neonatology. A high-risk baby might be cared for by a perinatologist before birth and by a neonatologist after birth. The word "perinatology" is a linguistic sandwich of the Greek "peri-" meaning "around or about", "natal" from the Latin "natus" meaning "born" and "ology" from the Greek "logos" meaning "treatise or study of."