The exegesis of that particular Bible verse is complicated.
For example, this very interpretation:
Manslaughter is not murder. A person being accidentally hurt during a fight between third parties would be manslaughter, not murder, according to traditional Biblical law.
In fact, it is assuming that the child is born alive, or else it would use the word "miscarry" and not "premature birth".
Whether "harm results" could perfectly refer to whether the woman is killed. Accidental manslaughter is not murder, but if a pregnant woman is killed by accident, THEN it calls blood for blood.
It is a plausible interpretation, and one of the interpretations that I've read.
It might not be the CORRECT one, but it's plausible.
If the killing that deserves blood for blood is that of the unborn, why is that unborn more than other victim of manslaughter?
Why doesn't use "miscarry" when it refers to the baby who would be dead, and "premature birth" when it results in a live baby. Y'know, instead of an obscure "harm is/is not done" unless it's referring to whether the harm is for the mother?