A fetus is not a baby, period. A baby is a different part of the life-cycle.Do you know what the different stages are within the human life cycle? Fetus and adult are 2 of them. But at no point does calling a baby a "fetus" make it anything less then a baby or a human being.
A fetus may or may not be LEGALLY or MORALLY a human being. But you cannot assume it is just because it's a stage in the life cycle.