Depends on gestation. If the woman is 3+ months pregnant that isn't just clumps of cells anymore the fetus has human shape. And usually a person 3+ months pregnant is probably planning on keeping the child, so if the pregnant person is murdered they essentially ended 2 lives and are charge as such.

If the pregnant person is less than 3 months pregnant it's really up in the air for the court to decide based of what the victim knew about their pregnancy. If they where only 2 weeks pregnant and unaware it probably wouldn't be brought up in court as 2 murders. Unless they knew the victim intended to keep the child or was trying to get pregnant around the time they where murdered.