A premature baby is a baby born at less than 37 weeks gestation.

Babies, whether born prematurely, or born at term, may be classified based on their birth weight. A baby classified as low birth weight (LBW) is born at less than 2500 g. A very low birth weight baby (VLBW) is born between 1000 – 1500 g, and an extremely low birth weight (ELBW) baby is born less than 1000g. 

Reference: AbbVie Corporation (Ed.). (2015). Preemie Parent Handbook (4th ed.). Canada: AbbVie Corportation.