Should causing harm to a fetus in a criminal assault be a second crime?

If a person harms or even kills a fetus while assaulting a pregnant woman, is that an additional crime, over and above the assault of the pregnant woman? If so, what should the charge be for this second crime? Alternatively, is the harm to the fetus included in the charge of assault against the pregnant woman herself? Or should the harm to the fetus be considered harm to the woman's private property? Also, should it matter if the assailant didn't know that the woman was pregnant? I think the anti-abortion activists will say that punishing the assailant for harm to the fetus only makes sense if the fetus is recognized as a separate person with rights. Are they wrong?