Extremely low birth weight baby: A baby born very prematurely weighing between 401 and 1000 grams (about 14 to 35 ounces) at birth. Extremely low birth weight (ELBW) babies are at the lower limits of viability.

If ELBW babies survive, they are at elevated risk for neurological abnormalities, hearing and visual impairment, and developmental delay in infancy. The lower a baby's weight at birth, the more likely the child is to be subject to such problems.