a very young child (birth to 1 year) who has not yet begun to walk or talk

infant who shows signs of life after birth

an infant born weighing less than 5.5 pounds (2500 grams) regardless of gestational age

infant born after 42 weeks of gestation; usually shows signs of placental insufficiency

an infant that is born prior to 37 weeks of gestation

an infant whose size and weight are considerably less than the average for babies of the same age