[This discussion is in response to this book review.]
Since most abortions occur early in pregnancy, it is at least curious to me (if not troubling) that the generic term "fetus" is used when discussing the matter, including by those who support a broad right to choose whether or not to have an abortion. But, though the matter often arises in that context, the below discussion suggests it is not limited to that area.
Medically, it appears that the norm is to define the word to mean development after the eighth week after fertilization. Before this, in the time in which most abortions and many natural miscarriages occur, is the embryonic stage. Colloquially, this also is different from "the fetal" stage. For instance, some don't tell others about a pregnancy before late in the first trimester. Many who have mixed views about abortion think it can be acceptable for various reasons at this stage, including as a religious and moral matter. The pregnant person also often doesn't look the part this early, nor treated as such by others, though they do feel the part in various respects.
By treating very early periods in the pregnancy as involving a "fetus," the conversation is altered. A visual picture emerges with that term, particularly of a fetus in a later stage that looks much like a newborn baby. There are various stages of pregnancy. "The fetus" is generally in at least the second stage [maybe third, if one thinks pregnancy begins at conception] and an open-ended use of the term is questionable.
It is therefore troubling that the "unborn" and "fetus" is used so interchangeably, even among those who should know better.