Even bacteria are "ALIVE" by scientific terms. You'll understand when you reach high school & take biology class.
Life is defined as the condition that distinguishes organisms from inorganic objects and dead organisms, being manifested by growth through metabolism, reproduction, and the power of adaptation to environment through changes originating internally.(
life definition | Dictionary.com) A fetus is not dead, and certainly isn't inorganic.
Understand that law is made by politicians, who seldom, if ever, rely on science alone to base a decision. The legal definition of human life is a wholly political one, completely separate from any scientific definition.