When is a fetus considered a human life under u.s. law?

Fetus: When a fetus has reached 24 weeks estimated gestational age it is considered to be a viable fetus and therefore afforded all medical efforts to maintain life if born. Prior to this gestational age the fetus is considered to be nonviable.

At birth: Us (federal) law only recognizes life after being born. A number of states have passed laws defining life at fetal heart origination, or fetal movement, or specific times like 2nd or 3rd trimester. A few want to define a fertilized egg as being a human life. There is a strong religious anti-abortion issue here. Note that 80% of fertilized eggs pass spontaneosly - defined as abortion by some.